diff --git a/src/builtin.cpp b/src/builtin.cpp
index be3c98fbe..76e235813 100644
--- a/src/builtin.cpp
+++ b/src/builtin.cpp
@@ -19,7 +19,7 @@
 
 #include <errno.h>
 #include <stdlib.h>
-#include <string.h>
+#include <cstring>
 #include <unistd.h>
 #include <cwchar>
 
@@ -97,7 +97,7 @@ int builtin_count_args(const wchar_t *const *argv) {
 /// This function works like wperror, but it prints its result into the streams.err string instead
 /// to stderr. Used by the builtin commands.
 void builtin_wperror(const wchar_t *s, io_streams_t &streams) {
-    char *err = strerror(errno);
+    char *err = std::strerror(errno);
     if (s != NULL) {
         streams.err.append(s);
         streams.err.append(L": ");
diff --git a/src/builtin_math.cpp b/src/builtin_math.cpp
index a1fb48d25..7798fe1a8 100644
--- a/src/builtin_math.cpp
+++ b/src/builtin_math.cpp
@@ -3,7 +3,7 @@
 
 #include <errno.h>
 #include <stddef.h>
-#include <string.h>
+#include <cstring>
 
 #include <algorithm>
 #include <cmath>
diff --git a/src/builtin_printf.cpp b/src/builtin_printf.cpp
index 1bcf05cc8..d12d9c596 100644
--- a/src/builtin_printf.cpp
+++ b/src/builtin_printf.cpp
@@ -57,7 +57,7 @@
 #include <stddef.h>
 #include <stdint.h>
 #include <stdlib.h>
-#include <string.h>
+#include <cstring>
 #include <sys/types.h>
 #include <cwchar>
 #include <wctype.h>
@@ -238,7 +238,7 @@ void builtin_printf_state_t::verify_numeric(const wchar_t *s, const wchar_t *end
         if (errcode == ERANGE) {
             this->fatal_error(L"%ls: %ls", s, _(L"Number out of range"));
         } else {
-            this->fatal_error(L"%ls: %s", s, strerror(errcode));
+            this->fatal_error(L"%ls: %s", s, std::strerror(errcode));
         }
     } else if (*end) {
         if (s == end)
diff --git a/src/builtin_pwd.cpp b/src/builtin_pwd.cpp
index ca668b0ea..66fb64efc 100644
--- a/src/builtin_pwd.cpp
+++ b/src/builtin_pwd.cpp
@@ -1,7 +1,7 @@
 // Implementation of the pwd builtin.
 #include "config.h"  // IWYU pragma: keep
 
-#include <string.h>
+#include <cstring>
 
 #include "builtin.h"
 #include "builtin_pwd.h"
@@ -58,7 +58,7 @@ int builtin_pwd(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
         if (auto real_pwd = wrealpath(pwd)) {
             pwd = std::move(*real_pwd);
         } else {
-            const char *error = strerror(errno);
+            const char *error = std::strerror(errno);
             streams.err.append_format(L"%ls: realpath failed:", cmd, error);
             return STATUS_CMD_ERROR;
         }
diff --git a/src/builtin_read.cpp b/src/builtin_read.cpp
index 523fb2d9e..a0f1ab91a 100644
--- a/src/builtin_read.cpp
+++ b/src/builtin_read.cpp
@@ -6,7 +6,7 @@
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
+#include <cstring>
 #include <unistd.h>
 #include <cwchar>
 
@@ -319,7 +319,7 @@ static int read_one_char_at_a_time(int fd, wcstring &buff, int nchars, bool spli
             } else {
                 size_t sz = std::mbrtowc(&res, &b, 1, &state);
                 if (sz == (size_t)-1) {
-                    memset(&state, 0, sizeof(state));
+                    std::memset(&state, 0, sizeof(state));
                 } else if (sz != (size_t)-2) {
                     finished = true;
                 }
diff --git a/src/builtin_realpath.cpp b/src/builtin_realpath.cpp
index 552eae5c1..62edae85b 100644
--- a/src/builtin_realpath.cpp
+++ b/src/builtin_realpath.cpp
@@ -3,7 +3,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
+#include <cstring>
 #include <cwchar>
 
 #include "builtin.h"
@@ -43,7 +43,7 @@ int builtin_realpath(parser_t &parser, io_streams_t &streams, wchar_t **argv) {
             // realpath() just couldn't do it. Report the error and make it clear
             // this is an error from our builtin, not the system's realpath.
             streams.err.append_format(L"builtin %ls: %ls: %s\n", cmd, argv[optind],
-                                      strerror(errno));
+                                      std::strerror(errno));
         } else {
             // Who knows. Probably a bug in our wrealpath() implementation.
             streams.err.append_format(_(L"builtin %ls: Invalid path: %ls\n"), cmd, argv[optind]);
diff --git a/src/builtin_set.cpp b/src/builtin_set.cpp
index c57b1d60f..3a18e5a09 100644
--- a/src/builtin_set.cpp
+++ b/src/builtin_set.cpp
@@ -4,7 +4,7 @@
 #include <errno.h>
 #include <stddef.h>
 #include <stdlib.h>
-#include <string.h>
+#include <cstring>
 #include <sys/stat.h>
 #include <unistd.h>
 #include <cwchar>
@@ -295,7 +295,7 @@ static bool validate_path_warning_on_colons(const wchar_t *cmd,
             any_success = true;
         } else if (looks_like_colon_sep) {
             streams.err.append_format(BUILTIN_SET_PATH_ERROR, cmd, key, dir.c_str(),
-                                      strerror(errno));
+                                      std::strerror(errno));
             streams.err.append_format(BUILTIN_SET_PATH_HINT, cmd, key, key,
                                       std::wcschr(dir.c_str(), L':') + 1);
         }
diff --git a/src/builtin_test.cpp b/src/builtin_test.cpp
index b49fa7bb6..3951a7ecc 100644
--- a/src/builtin_test.cpp
+++ b/src/builtin_test.cpp
@@ -5,7 +5,7 @@
 
 #include <errno.h>
 #include <stdarg.h>
-#include <string.h>
+#include <cstring>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
@@ -675,7 +675,7 @@ static bool parse_number(const wcstring &arg, number_t *number, wcstring_list_t
             errors.push_back(format_string(_(L"Integer %lld in '%ls' followed by non-digit"),
                                            integral, argcs));
         } else {
-            errors.push_back(format_string(L"%s: '%ls'", strerror(errno), argcs));
+            errors.push_back(format_string(L"%s: '%ls'", std::strerror(errno), argcs));
         }
         return false;
     }
diff --git a/src/color.cpp b/src/color.cpp
index 4dd60ef46..ceaec1ffd 100644
--- a/src/color.cpp
+++ b/src/color.cpp
@@ -11,7 +11,7 @@
 #include "fallback.h"  // IWYU pragma: keep
 
 bool rgb_color_t::try_parse_special(const wcstring &special) {
-    memset(&data, 0, sizeof data);
+    std::memset(&data, 0, sizeof data);
     const wchar_t *name = special.c_str();
     if (!wcscasecmp(name, L"normal")) {
         this->type = type_normal;
@@ -108,7 +108,7 @@ static unsigned char convert_color(const unsigned char rgb[3], const uint32_t *c
 }
 
 bool rgb_color_t::try_parse_rgb(const wcstring &name) {
-    memset(&data, 0, sizeof data);
+    std::memset(&data, 0, sizeof data);
     // We support the following style of rgb formats (case insensitive):
     //  #FA3
     //  #F3A035
@@ -185,7 +185,7 @@ wcstring_list_t rgb_color_t::named_color_names() {
 }
 
 bool rgb_color_t::try_parse_named(const wcstring &str) {
-    memset(&data, 0, sizeof data);
+    std::memset(&data, 0, sizeof data);
     size_t max = sizeof named_colors / sizeof *named_colors;
     for (size_t idx = 0; idx < max; idx++) {
         if (0 == wcscasecmp(str.c_str(), named_colors[idx].name)) {
@@ -299,7 +299,7 @@ void rgb_color_t::parse(const wcstring &str) {
     if (!success) success = try_parse_named(str);
     if (!success) success = try_parse_rgb(str);
     if (!success) {
-        memset(&this->data, 0, sizeof this->data);
+        std::memset(&this->data, 0, sizeof this->data);
         this->type = type_none;
     }
 }
diff --git a/src/color.h b/src/color.h
index ec6d29dbb..2e437b966 100644
--- a/src/color.h
+++ b/src/color.h
@@ -2,7 +2,7 @@
 #ifndef FISH_COLOR_H
 #define FISH_COLOR_H
 
-#include <string.h>
+#include <cstring>
 
 #include <string>
 
@@ -159,7 +159,7 @@ class rgb_color_t {
 
     /// Compare two colors for equality.
     bool operator==(const rgb_color_t &other) const {
-        return type == other.type && !memcmp(&data, &other.data, sizeof data);
+        return type == other.type && !std::memcmp(&data, &other.data, sizeof data);
     }
 
     /// Compare two colors for inequality.
diff --git a/src/common.cpp b/src/common.cpp
index ba7da173d..cb158912f 100644
--- a/src/common.cpp
+++ b/src/common.cpp
@@ -14,7 +14,7 @@
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
+#include <cstring>
 #include <sys/stat.h>
 #include <sys/time.h>
 #include <termios.h>
@@ -141,7 +141,7 @@ long convert_digit(wchar_t d, int base) {
 }
 
 /// Test whether the char is a valid hex digit as used by the `escape_string_*()` functions.
-static bool is_hex_digit(int c) { return strchr("0123456789ABCDEF", c) != NULL; }
+static bool is_hex_digit(int c) { return std::strchr("0123456789ABCDEF", c) != NULL; }
 
 /// This is a specialization of `convert_digit()` that only handles base 16 and only uppercase.
 long convert_hex_digit(wchar_t d) {
@@ -170,8 +170,8 @@ bool is_windows_subsystem_for_linux() {
         uname(&info);
 
         // Sample utsname.release under WSL: 4.4.0-17763-Microsoft
-        if (strstr(info.release, "Microsoft") != nullptr) {
-            const char *dash = strchr(info.release, '-');
+        if (std::strstr(info.release, "Microsoft") != nullptr) {
+            const char *dash = std::strchr(info.release, '-');
             if (dash == nullptr || strtod(dash + 1, nullptr) < 17763) {
                 debug(1, "This version of WSL is not supported and fish will probably not work correctly!\n"
                         "Please upgrade to Windows 10 1809 (17763) or higher to use fish!");
@@ -346,11 +346,11 @@ static wcstring str2wcs_internal(const char *in, const size_t in_len) {
             wc = ENCODE_DIRECT_BASE + (unsigned char)in[in_pos];
             result.push_back(wc);
             in_pos++;
-            memset(&state, 0, sizeof state);
+            std::memset(&state, 0, sizeof state);
         } else if (ret == 0) {  // embedded null byte!
             result.push_back(L'\0');
             in_pos++;
-            memset(&state, 0, sizeof state);
+            std::memset(&state, 0, sizeof state);
         } else {  // normal case
             result.push_back(wc);
             in_pos += ret;
@@ -362,7 +362,7 @@ static wcstring str2wcs_internal(const char *in, const size_t in_len) {
 
 wcstring str2wcstring(const char *in, size_t len) { return str2wcs_internal(in, len); }
 
-wcstring str2wcstring(const char *in) { return str2wcs_internal(in, strlen(in)); }
+wcstring str2wcstring(const char *in) { return str2wcs_internal(in, std::strlen(in)); }
 
 wcstring str2wcstring(const std::string &in) {
     // Handles embedded nulls!
@@ -423,11 +423,11 @@ std::string wcs2string(const wcstring &input) {
             converted[0] = wc;
             result.append(converted, 1);
         } else {
-            memset(converted, 0, sizeof converted);
+            std::memset(converted, 0, sizeof converted);
             size_t len = std::wcrtomb(converted, wc, &state);
             if (len == (size_t)-1) {
                 debug(1, L"Wide character U+%4X has no narrow representation", wc);
-                memset(&state, 0, sizeof(state));
+                std::memset(&state, 0, sizeof(state));
             } else {
                 result.append(converted, len);
             }
@@ -467,7 +467,7 @@ static char *wcs2str_internal(const wchar_t *in, char *out) {
             size_t len = std::wcrtomb(&out[out_pos], in[in_pos], &state);
             if (len == (size_t)-1) {
                 debug(1, L"Wide character U+%4X has no narrow representation", in[in_pos]);
-                memset(&state, 0, sizeof(state));
+                std::memset(&state, 0, sizeof(state));
             } else {
                 out_pos += len;
             }
@@ -707,8 +707,8 @@ void debug_safe(int level, const char *msg, const char *param1, const char *para
     size_t param_idx = 0;
     const char *cursor = msg;
     while (*cursor != '\0') {
-        const char *end = strchr(cursor, '%');
-        if (end == NULL) end = cursor + strlen(cursor);
+        const char *end = std::strchr(cursor, '%');
+        if (end == NULL) end = cursor + std::strlen(cursor);
 
         ignore_result(write(STDERR_FILENO, cursor, end - cursor));
 
@@ -717,7 +717,7 @@ void debug_safe(int level, const char *msg, const char *param1, const char *para
             assert(param_idx < sizeof params / sizeof *params);
             const char *format = params[param_idx++];
             if (!format) format = "(null)";
-            ignore_result(write(STDERR_FILENO, format, strlen(format)));
+            ignore_result(write(STDERR_FILENO, format, std::strlen(format)));
             cursor = end + 2;
         } else if (end[0] == '\0') {
             // Must be at the end of the string.
@@ -2138,7 +2138,7 @@ void append_str(char *buff, const char *str, size_t *inout_idx, size_t max_len)
 void format_size_safe(char buff[128], unsigned long long sz) {
     const size_t buff_size = 128;
     const size_t max_len = buff_size - 1;  // need to leave room for a null terminator
-    memset(buff, 0, buff_size);
+    std::memset(buff, 0, buff_size);
     size_t idx = 0;
     const char *const sz_name[] = {"kB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB", NULL};
     if (sz < 1) {
@@ -2403,7 +2403,7 @@ void redirect_tty_output() {
 [[noreturn]] void __fish_assert(const char *msg, const char *file, size_t line, int error) {
     if (error) {
         debug(0, L"%s:%zu: failed assertion: %s: errno %d (%s)", file, line, msg, error,
-              strerror(error));
+              std::strerror(error));
     } else {
         debug(0, L"%s:%zu: failed assertion: %s", file, line, msg);
     }
diff --git a/src/env.cpp b/src/env.cpp
index 13d95763e..40bc26b34 100644
--- a/src/env.cpp
+++ b/src/env.cpp
@@ -9,7 +9,7 @@
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
+#include <cstring>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <time.h>
@@ -411,7 +411,7 @@ static void init_locale(const environment_t &vars) {
     debug(5, L"old LC_MESSAGES locale: '%s'", old_msg_locale);
     debug(5, L"new LC_MESSAGES locale: '%s'", new_msg_locale);
 #ifdef HAVE__NL_MSG_CAT_CNTR
-    if (strcmp(old_msg_locale, new_msg_locale)) {
+    if (std::strcmp(old_msg_locale, new_msg_locale)) {
         // Make change known to GNU gettext.
         extern int _nl_msg_cat_cntr;
         _nl_msg_cat_cntr++;
@@ -455,7 +455,7 @@ static bool does_term_support_setting_title(const environment_t &vars) {
 
         char buf[PATH_MAX];
         int retval = ttyname_r(STDIN_FILENO, buf, PATH_MAX);
-        if (retval != 0 || strstr(buf, "tty") || strstr(buf, "/vc/")) return false;
+        if (retval != 0 || std::strstr(buf, "tty") || std::strstr(buf, "/vc/")) return false;
     }
 
     return true;
diff --git a/src/env_universal_common.cpp b/src/env_universal_common.cpp
index f30cbad56..cde707860 100644
--- a/src/env_universal_common.cpp
+++ b/src/env_universal_common.cpp
@@ -17,7 +17,7 @@
 #include <stddef.h>
 #include <stdint.h>
 #include <stdlib.h>
-#include <string.h>
+#include <cstring>
 #ifdef __CYGWIN__
 #include <sys/mman.h>
 #endif
@@ -123,7 +123,7 @@ static maybe_t<wcstring> default_vars_path() {
 /// On success, updates the cursor to just past the command.
 static bool match(const wchar_t **inout_cursor, const char *cmd) {
     const wchar_t *cursor = *inout_cursor;
-    size_t len = strlen(cmd);
+    size_t len = std::strlen(cmd);
     if (!std::equal(cmd, cmd + len, cursor)) {
         return false;
     }
@@ -445,7 +445,7 @@ bool env_universal_t::write_to_fd(int fd, const wcstring &path) {
     bool success = true;
     std::string contents = serialize_with_vars(vars);
     if (write_loop(fd, contents.data(), contents.size()) < 0) {
-        const char *error = strerror(errno);
+        const char *error = std::strerror(errno);
         debug(0, _(L"Unable to write to universal variables file '%ls': %s"), path.c_str(), error);
         success = false;
     }
@@ -460,7 +460,7 @@ bool env_universal_t::write_to_fd(int fd, const wcstring &path) {
 bool env_universal_t::move_new_vars_file_into_place(const wcstring &src, const wcstring &dst) {
     int ret = wrename(src, dst);
     if (ret != 0) {
-        const char *error = strerror(errno);
+        const char *error = std::strerror(errno);
         debug(0, _(L"Unable to rename file from '%ls' to '%ls': %s"), src.c_str(), dst.c_str(),
               error);
     }
@@ -521,7 +521,7 @@ bool env_universal_t::open_temporary_file(const wcstring &directory, wcstring *o
     }
 
     if (!success) {
-        const char *error = strerror(saved_errno);
+        const char *error = std::strerror(saved_errno);
         debug(0, _(L"Unable to open temporary file '%ls': %s"), out_path->c_str(), error);
     }
     return success;
@@ -583,7 +583,7 @@ bool env_universal_t::open_and_acquire_lock(const wcstring &path, int *out_fd) {
                 continue;
             }
 #endif
-            const char *error = strerror(errno);
+            const char *error = std::strerror(errno);
             debug(0, _(L"Unable to open universal variable file '%ls': %s"), path.c_str(), error);
             break;
         }
@@ -801,7 +801,7 @@ uvar_format_t env_universal_t::format_for_contents(const std::string &s) {
         if (sscanf(line.c_str(), "# VERSION: %64s", versionbuf) != 1) continue;
 
         // Try reading the version.
-        if (!strcmp(versionbuf, UVARS_VERSION_3_0)) {
+        if (!std::strcmp(versionbuf, UVARS_VERSION_3_0)) {
             return uvar_format_t::fish_3_0;
         } else {
             // Unknown future version.
@@ -946,7 +946,7 @@ static bool get_mac_address(unsigned char macaddr[MAC_ADDRESS_MAX_LEN],
         strncpy((char *)r.ifr_name, interface, sizeof r.ifr_name - 1);
         r.ifr_name[sizeof r.ifr_name - 1] = 0;
         if (ioctl(dummy, SIOCGIFHWADDR, &r) >= 0) {
-            memcpy(macaddr, r.ifr_hwaddr.sa_data, MAC_ADDRESS_MAX_LEN);
+            std::memcpy(macaddr, r.ifr_hwaddr.sa_data, MAC_ADDRESS_MAX_LEN);
             result = true;
         }
         close(dummy);
@@ -978,7 +978,7 @@ static bool get_mac_address(unsigned char macaddr[MAC_ADDRESS_MAX_LEN],
 
             size_t alen = sdl.sdl_alen;
             if (alen > MAC_ADDRESS_MAX_LEN) alen = MAC_ADDRESS_MAX_LEN;
-            memcpy(macaddr, sdl.sdl_data + sdl.sdl_nlen, alen);
+            std::memcpy(macaddr, sdl.sdl_data + sdl.sdl_nlen, alen);
             ok = true;
             break;
         }
@@ -1053,7 +1053,7 @@ class universal_notifier_shmem_poller_t : public universal_notifier_t {
         bool errored = false;
         int fd = shm_open(path, O_RDWR | O_CREAT, 0600);
         if (fd < 0) {
-            const char *error = strerror(errno);
+            const char *error = std::strerror(errno);
             debug(0, _(L"Unable to open shared memory with path '%s': %s"), path, error);
             errored = true;
         }
@@ -1063,7 +1063,7 @@ class universal_notifier_shmem_poller_t : public universal_notifier_t {
         if (!errored) {
             struct stat buf = {};
             if (fstat(fd, &buf) < 0) {
-                const char *error = strerror(errno);
+                const char *error = std::strerror(errno);
                 debug(0, _(L"Unable to fstat shared memory object with path '%s': %s"), path,
                       error);
                 errored = true;
@@ -1074,7 +1074,7 @@ class universal_notifier_shmem_poller_t : public universal_notifier_t {
         // Set the size, if it's too small.
         bool set_size = !errored && size < (off_t)sizeof(universal_notifier_shmem_t);
         if (set_size && ftruncate(fd, sizeof(universal_notifier_shmem_t)) < 0) {
-            const char *error = strerror(errno);
+            const char *error = std::strerror(errno);
             debug(0, _(L"Unable to truncate shared memory object with path '%s': %s"), path, error);
             errored = true;
         }
@@ -1084,7 +1084,7 @@ class universal_notifier_shmem_poller_t : public universal_notifier_t {
             void *addr = mmap(NULL, sizeof(universal_notifier_shmem_t), PROT_READ | PROT_WRITE,
                               MAP_SHARED, fd, 0);
             if (addr == MAP_FAILED) {
-                const char *error = strerror(errno);
+                const char *error = std::strerror(errno);
                 debug(0, _(L"Unable to memory map shared memory object with path '%s': %s"), path,
                       error);
                 this->region = NULL;
@@ -1489,7 +1489,7 @@ void universal_notifier_named_pipe_t::make_pipe(const wchar_t *test_path) {
 
     int mkfifo_status = mkfifo(narrow_path.c_str(), 0600);
     if (mkfifo_status == -1 && errno != EEXIST) {
-        const char *error = strerror(errno);
+        const char *error = std::strerror(errno);
         const wchar_t *errmsg = _(L"Unable to make a pipe for universal variables using '%ls': %s");
         debug(0, errmsg, vars_path.c_str(), error);
         pipe_fd = -1;
@@ -1498,7 +1498,7 @@ void universal_notifier_named_pipe_t::make_pipe(const wchar_t *test_path) {
 
     int fd = wopen_cloexec(vars_path, O_RDWR | O_NONBLOCK, 0600);
     if (fd < 0) {
-        const char *error = strerror(errno);
+        const char *error = std::strerror(errno);
         const wchar_t *errmsg = _(L"Unable to open a pipe for universal variables using '%ls': %s");
         debug(0, errmsg, vars_path.c_str(), error);
         pipe_fd = -1;
diff --git a/src/exec.cpp b/src/exec.cpp
index 7d55ca99e..05ebea52a 100644
--- a/src/exec.cpp
+++ b/src/exec.cpp
@@ -14,7 +14,7 @@
 #include <spawn.h>
 #endif
 #include <stdio.h>
-#include <string.h>
+#include <cstring>
 #include <sys/wait.h>
 #include <unistd.h>
 #include <stack>
@@ -78,7 +78,7 @@ static bool redirection_is_to_real_file(const shared_ptr<io_data_t> &io) {
     if (io && io->io_mode == io_mode_t::file) {
         // It's a file redirection. Compare the path to /dev/null.
         const char *path = static_cast<const io_file_t *>(io.get())->filename_cstr;
-        if (strcmp(path, "/dev/null") != 0) {
+        if (std::strcmp(path, "/dev/null") != 0) {
             // It's not /dev/null.
             result = true;
         }
@@ -104,9 +104,9 @@ char *get_interpreter(const char *command, char *interpreter, size_t buff_size)
         close(fd);
     }
 
-    if (strncmp(interpreter, "#! /", 4) == 0) {
+    if (std::strncmp(interpreter, "#! /", 4) == 0) {
         return interpreter + 3;
-    } else if (strncmp(interpreter, "#!/", 3) == 0) {
+    } else if (std::strncmp(interpreter, "#!/", 3) == 0) {
         return interpreter + 2;
     }
 
@@ -1126,7 +1126,7 @@ static int exec_subshell_internal(const wcstring &cmd, parser_t &parser, wcstrin
             const char *cursor = begin;
             while (cursor < end) {
                 // Look for the next separator.
-                const char *stop = (const char *)memchr(cursor, '\n', end - cursor);
+                const char *stop = (const char *)std::memchr(cursor, '\n', end - cursor);
                 const bool hit_separator = (stop != NULL);
                 if (!hit_separator) {
                     // If it's not found, just use the end.
diff --git a/src/expand.cpp b/src/expand.cpp
index 4c7532fc8..42c44d8fa 100644
--- a/src/expand.cpp
+++ b/src/expand.cpp
@@ -7,7 +7,7 @@
 #include <stdarg.h>
 #include <stddef.h>
 #include <stdlib.h>
-#include <string.h>
+#include <cstring>
 #include <unistd.h>
 #include <cwchar>
 #include <wctype.h>
@@ -1156,7 +1156,7 @@ expand_error_t expand_to_command_and_args(const wcstring &instr, const environme
 
 static std::string escape_single_quoted_hack_hack_hack_hack(const char *str) {
     std::string result;
-    size_t len = strlen(str);
+    size_t len = std::strlen(str);
     result.reserve(len + 2);
     result.push_back('\'');
     for (size_t i = 0; i < len; i++) {
diff --git a/src/fallback.cpp b/src/fallback.cpp
index f028e3f05..b944c0406 100644
--- a/src/fallback.cpp
+++ b/src/fallback.cpp
@@ -14,7 +14,7 @@
 #include <stdarg.h>  // IWYU pragma: keep
 #include <stdio.h>   // IWYU pragma: keep
 #include <stdlib.h>
-#include <string.h>
+#include <cstring>
 #include <sys/stat.h>   // IWYU pragma: keep
 #include <sys/types.h>  // IWYU pragma: keep
 #include <unistd.h>
@@ -81,7 +81,7 @@ int fish_mkstemp_cloexec(char *name_template) {
         return 0;
     }
 
-    memcpy(out, in, sizeof(wchar_t) * (len + 1));
+    std::memcpy(out, in, sizeof(wchar_t) * (len + 1));
     return out;
 }
 
diff --git a/src/fish.cpp b/src/fish.cpp
index 4ec0ab190..21832b265 100644
--- a/src/fish.cpp
+++ b/src/fish.cpp
@@ -27,7 +27,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
+#include <cstring>
 #include <sys/stat.h>
 #include <unistd.h>
 #include <cwchar>
@@ -69,9 +69,9 @@ class fish_cmd_opts_t {
 static const char *s_profiling_output_filename = NULL;
 
 static bool has_suffix(const std::string &path, const char *suffix, bool ignore_case) {
-    size_t pathlen = path.size(), suffixlen = strlen(suffix);
+    size_t pathlen = path.size(), suffixlen = std::strlen(suffix);
     return pathlen >= suffixlen &&
-           !(ignore_case ? strcasecmp : strcmp)(path.c_str() + pathlen - suffixlen, suffix);
+           !(ignore_case ? strcasecmp : std::strcmp)(path.c_str() + pathlen - suffixlen, suffix);
 }
 
 /// Modifies the given path by calling realpath. Returns true if realpath succeeded, false
@@ -122,7 +122,7 @@ static struct config_paths_t determine_config_directory_paths(const char *argv0)
                 bool seems_installed = (suffix == installed_suffix);
 
                 wcstring base_path = str2wcstring(exec_path);
-                base_path.resize(base_path.size() - strlen(suffix));
+                base_path.resize(base_path.size() - std::strlen(suffix));
 
                 paths.data = base_path + (seems_installed ? L"/share/fish" : L"/share");
                 paths.sysconf = base_path + (seems_installed ? L"/etc/fish" : L"/etc");
diff --git a/src/fish_indent.cpp b/src/fish_indent.cpp
index 61633dc10..01d3a3b94 100644
--- a/src/fish_indent.cpp
+++ b/src/fish_indent.cpp
@@ -23,7 +23,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
+#include <cstring>
 #include <wctype.h>
 
 #include <cwchar>
@@ -63,7 +63,7 @@ static wcstring read_file(FILE *f) {
                     // Illegal byte sequence. Try to skip past it.
                     clearerr(f);
                     int ch = fgetc(f); // for printing the warning, and seeks forward 1 byte.
-                    debug(1, "%s (byte=%X)", strerror(errno), ch);
+                    debug(1, "%s (byte=%X)", std::strerror(errno), ch);
                     ret = 1;
                     continue;
                 } else {
@@ -518,7 +518,7 @@ int main(int argc, char *argv[]) {
             fclose(fh);
             output_location = *argv;
         } else {
-            std::fwprintf(stderr, _(L"Opening \"%s\" failed: %s\n"), *argv, strerror(errno));
+            std::fwprintf(stderr, _(L"Opening \"%s\" failed: %s\n"), *argv, std::strerror(errno));
             exit(1);
         }
     } else {
@@ -549,7 +549,7 @@ int main(int argc, char *argv[]) {
                 exit(0);
             } else {
                 std::fwprintf(stderr, _(L"Opening \"%s\" failed: %s\n"), output_location,
-                         strerror(errno));
+                         std::strerror(errno));
                 exit(1);
             }
             break;
diff --git a/src/fish_key_reader.cpp b/src/fish_key_reader.cpp
index fba073944..be845c63b 100644
--- a/src/fish_key_reader.cpp
+++ b/src/fish_key_reader.cpp
@@ -14,7 +14,7 @@
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
+#include <cstring>
 #include <termios.h>
 #include <unistd.h>
 #include <cwchar>
@@ -62,7 +62,7 @@ static bool should_exit(wchar_t wc) {
         std::fwprintf(stderr, L"Press [ctrl-%c] again to exit\n", shell_modes.c_cc[VEOF] + 0x40);
         return false;
     }
-    return memcmp(recent_chars, "exit", 4) == 0 || memcmp(recent_chars, "quit", 4) == 0;
+    return std::memcmp(recent_chars, "exit", 4) == 0 || std::memcmp(recent_chars, "quit", 4) == 0;
 }
 
 /// Return the name if the recent sequence of characters matches a known terminfo sequence.
@@ -265,7 +265,7 @@ static void install_our_signal_handlers() {
 
     for (int signo = 1; signo < 32; signo++) {
         if (sigaction(signo, &new_sa, &old_sa) != -1) {
-            memcpy(&old_sigactions[signo], &old_sa, sizeof(old_sa));
+            std::memcpy(&old_sigactions[signo], &old_sa, sizeof(old_sa));
             if (old_sa.sa_handler == SIG_IGN) {
                 debug(3, "signal #%d (%ls) was being ignored", signo, sig2wcs(signo));
             }
diff --git a/src/fish_tests.cpp b/src/fish_tests.cpp
index 9059cf101..e459dc504 100644
--- a/src/fish_tests.cpp
+++ b/src/fish_tests.cpp
@@ -14,7 +14,7 @@
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
+#include <cstring>
 #include <sys/select.h>
 #include <sys/stat.h>
 #include <sys/time.h>
@@ -89,7 +89,7 @@ static bool should_test_function(const char *func_name) {
         result = true;
     } else {
         for (size_t i = 0; s_arguments[i] != NULL; i++) {
-            if (!strncmp(func_name, s_arguments[i], strlen(s_arguments[i]))) {
+            if (!std::strncmp(func_name, s_arguments[i], std::strlen(s_arguments[i]))) {
                 // Prefix match.
                 result = true;
                 break;
@@ -448,14 +448,14 @@ static void test_format() {
     for (i = 0; i < sizeof tests / sizeof *tests; i++) {
         char buff[128];
         format_size_safe(buff, tests[i].val);
-        do_test(!strcmp(buff, tests[i].expected));
+        do_test(!std::strcmp(buff, tests[i].expected));
     }
 
     for (int j = -129; j <= 129; j++) {
         char buff1[128], buff2[128];
         format_long_safe(buff1, j);
         sprintf(buff2, "%d", j);
-        do_test(!strcmp(buff1, buff2));
+        do_test(!std::strcmp(buff1, buff2));
 
         wchar_t wbuf1[128], wbuf2[128];
         format_long_safe(wbuf1, j);
@@ -467,12 +467,12 @@ static void test_format() {
     char buff1[128], buff2[128];
     format_long_safe(buff1, q);
     sprintf(buff2, "%ld", q);
-    do_test(!strcmp(buff1, buff2));
+    do_test(!std::strcmp(buff1, buff2));
 }
 
 /// Helper to convert a narrow string to a sequence of hex digits.
 static char *str2hex(const char *input) {
-    char *output = (char *)malloc(5 * strlen(input) + 1);
+    char *output = (char *)malloc(5 * std::strlen(input) + 1);
     char *p = output;
     for (; *input; input++) {
         sprintf(p, "0x%02X ", (int)*input & 0xFF);
@@ -511,12 +511,12 @@ static void test_convert() {
                 L"wcs2str");
         }
 
-        if (strcmp(o, n)) {
+        if (std::strcmp(o, n)) {
             char *o2 = str2hex(o);
             char *n2 = str2hex(n);
             err(L"Line %d - %d: Conversion cycle of string:\n%4d chars: %s\n"
                 L"produced different string:\n%4d chars: %s",
-                __LINE__, i, strlen(o), o2, strlen(n), n2);
+                __LINE__, i, std::strlen(o), o2, std::strlen(n), n2);
             free(o2);
             free(n2);
         }
@@ -1258,7 +1258,7 @@ static void test_utf82wchar(const char *src, size_t slen, const wchar_t *dst, si
 
     if (res != size) {
         err(L"u2w: %s: FAILED (rv: %lu, must be %lu)", descr, size, res);
-    } else if (mem && memcmp(mem, dst, size * sizeof(*mem)) != 0) {
+    } else if (mem && std::memcmp(mem, dst, size * sizeof(*mem)) != 0) {
         err(L"u2w: %s: BROKEN", descr);
     }
 
@@ -1303,7 +1303,7 @@ static void test_wchar2utf8(const wchar_t *src, size_t slen, const char *dst, si
     size = wchar_to_utf8(src, slen, mem, dlen, flags);
     if (res != size) {
         err(L"w2u: %s: FAILED (rv: %lu, must be %lu)", descr, size, res);
-    } else if (dst && memcmp(mem, dst, size) != 0) {
+    } else if (dst && std::memcmp(mem, dst, size) != 0) {
         err(L"w2u: %s: BROKEN", descr);
     }
 
@@ -1459,7 +1459,7 @@ static void test_escape_sequences() {
         err(L"test_escape_sequences failed on line %d\n", __LINE__);
     if (escape_code_length(L"\x1B[2J") != 4)
         err(L"test_escape_sequences failed on line %d\n", __LINE__);
-    if (escape_code_length(L"\x1B[38;5;123mABC") != strlen("\x1B[38;5;123m"))
+    if (escape_code_length(L"\x1B[38;5;123mABC") != std::strlen("\x1B[38;5;123m"))
         err(L"test_escape_sequences failed on line %d\n", __LINE__);
     if (escape_code_length(L"\x1B@") != 2)
         err(L"test_escape_sequences failed on line %d\n", __LINE__);
@@ -3230,7 +3230,7 @@ static void test_universal_ok_to_save() {
     const char *contents = "# VERSION: 99999.99\n";
     FILE *fp = wfopen(UVARS_TEST_PATH, "w");
     assert(fp && "Failed to open UVARS_TEST_PATH for writing");
-    fwrite(contents, strlen(contents), 1, fp);
+    fwrite(contents, std::strlen(contents), 1, fp);
     fclose(fp);
 
     file_id_t before_id = file_id_for_path(UVARS_TEST_PATH);
@@ -5176,7 +5176,7 @@ int main(int argc, char **argv) {
             perror("getcwd");
             exit(-1);
         }
-        if (!strcmp(wd, "/")) {
+        if (!std::strcmp(wd, "/")) {
             std::fwprintf(stderr,
                      L"Unable to find 'tests' directory, which should contain file test.fish\n");
             exit(EXIT_FAILURE);
diff --git a/src/history.cpp b/src/history.cpp
index 1c7abddfb..d0deb6eb5 100644
--- a/src/history.cpp
+++ b/src/history.cpp
@@ -8,7 +8,7 @@
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
+#include <cstring>
 #include <cstdint>
 // We need the sys/file.h for the flock() declaration on Linux but not OS X.
 #include <sys/file.h>  // IWYU pragma: keep
@@ -75,10 +75,10 @@ static constexpr int max_save_tries = 1024;
 
 namespace {
 
+static size_t safe_strlen(const char *s) { return s ? std::strlen(s) : 0; }
 /// Helper class for certain output. This is basically a string that allows us to ensure we only
 /// flush at record boundaries, and avoids the copying of ostringstream. Have you ever tried to
 /// implement your own streambuf? Total insanity.
-static size_t safe_strlen(const char *s) { return s ? strlen(s) : 0; }
 class history_output_buffer_t {
     std::vector<char> buffer;
 
@@ -271,7 +271,7 @@ class history_file_contents_t {
                 ptr += amt;
             }
         }
-        memset(ptr, 0, remaining);
+        std::memset(ptr, 0, remaining);
         return true;
     }
 
@@ -350,7 +350,7 @@ static size_t read_line(const char *base, size_t cursor, size_t len, std::string
     // Locate the newline.
     assert(cursor <= len);
     const char *start = base + cursor;
-    const char *a_newline = (char *)memchr(start, '\n', len - cursor);
+    const char *a_newline = (char *)std::memchr(start, '\n', len - cursor);
     if (a_newline != NULL) {  // we found a newline
         result.assign(start, a_newline - start);
         // Return the amount to advance the cursor; skip over the newline.
@@ -513,7 +513,7 @@ static history_item_t decode_item_fish_2_0(const char *base, size_t len) {
                 size_t advance = read_line(base, cursor, len, line);
                 if (trim_leading_spaces(line) <= indent) break;
 
-                if (strncmp(line.c_str(), "- ", 2)) break;
+                if (std::strncmp(line.c_str(), "- ", 2)) break;
 
                 // We're going to consume this line.
                 cursor += advance;
@@ -636,7 +636,7 @@ static bool parse_timestamp(const char *str, time_t *out_when) {
 
     // Look for "when:".
     size_t when_len = 5;
-    if (strncmp(cursor, "when:", when_len) != 0) return false;
+    if (std::strncmp(cursor, "when:", when_len) != 0) return false;
     cursor += when_len;
 
     // Advance past spaces.
@@ -661,7 +661,7 @@ static const char *next_line(const char *start, size_t length) {
     const char *const end = start + length;
 
     // Skip past the next newline.
-    const char *nextline = (const char *)memchr(start, '\n', length);
+    const char *nextline = (const char *)std::memchr(start, '\n', length);
     if (!nextline || nextline >= end) {
         return NULL;
     }
@@ -671,7 +671,7 @@ static const char *next_line(const char *start, size_t length) {
     }
 
     // Make sure this new line is itself "newline terminated". If it's not, return NULL.
-    const char *next_newline = (const char *)memchr(nextline, '\n', end - nextline);
+    const char *next_newline = (const char *)std::memchr(nextline, '\n', end - nextline);
     if (!next_newline) {
         return NULL;
     }
@@ -694,7 +694,7 @@ static size_t offset_of_next_item_fish_2_0(const history_file_contents_t &conten
         const char *line_start = contents.address_at(cursor);
 
         // Advance the cursor to the next line.
-        const char *a_newline = (const char *)memchr(line_start, '\n', length - cursor);
+        const char *a_newline = (const char *)std::memchr(line_start, '\n', length - cursor);
         if (a_newline == NULL) break;
 
         // Advance the cursor past this line. +1 is for the newline.
@@ -707,26 +707,26 @@ static size_t offset_of_next_item_fish_2_0(const history_file_contents_t &conten
         if (a_newline - line_start < 3) continue;
 
         // Try to be a little YAML compatible. Skip lines with leading %, ---, or ...
-        if (!memcmp(line_start, "%", 1) || !memcmp(line_start, "---", 3) ||
-            !memcmp(line_start, "...", 3))
+        if (!std::memcmp(line_start, "%", 1) || !std::memcmp(line_start, "---", 3) ||
+            !std::memcmp(line_start, "...", 3))
             continue;
 
         // Hackish: fish 1.x rewriting a fish 2.0 history file can produce lines with lots of
         // leading "- cmd: - cmd: - cmd:". Trim all but one leading "- cmd:".
         const char *double_cmd = "- cmd: - cmd: ";
-        const size_t double_cmd_len = strlen(double_cmd);
+        const size_t double_cmd_len = std::strlen(double_cmd);
         while ((size_t)(a_newline - line_start) > double_cmd_len &&
-               !memcmp(line_start, double_cmd, double_cmd_len)) {
+               !std::memcmp(line_start, double_cmd, double_cmd_len)) {
             // Skip over just one of the - cmd. In the end there will be just one left.
-            line_start += strlen("- cmd: ");
+            line_start += std::strlen("- cmd: ");
         }
 
         // Hackish: fish 1.x rewriting a fish 2.0 history file can produce commands like "when:
         // 123456". Ignore those.
         const char *cmd_when = "- cmd:    when:";
-        const size_t cmd_when_len = strlen(cmd_when);
+        const size_t cmd_when_len = std::strlen(cmd_when);
         if ((size_t)(a_newline - line_start) >= cmd_when_len &&
-            !memcmp(line_start, cmd_when, cmd_when_len)) {
+            !std::memcmp(line_start, cmd_when, cmd_when_len)) {
             continue;
         }
 
@@ -1141,7 +1141,7 @@ wcstring history_search_t::current_string() const {
 }
 
 static void replace_all(std::string *str, const char *needle, const char *replacement) {
-    size_t needle_len = strlen(needle), replacement_len = strlen(replacement);
+    size_t needle_len = std::strlen(needle), replacement_len = std::strlen(replacement);
     size_t offset = 0;
     while ((offset = str->find(needle, offset)) != std::string::npos) {
         str->replace(offset, needle_len, replacement);
@@ -1820,7 +1820,7 @@ void history_t::populate_from_bash(FILE *stream) {
             }
 
             // Deal with the newline if present.
-            char *a_newline = strchr(buff, '\n');
+            char *a_newline = std::strchr(buff, '\n');
             if (a_newline) *a_newline = '\0';
             line.append(buff);
             if (a_newline) break;
diff --git a/src/input_common.cpp b/src/input_common.cpp
index 655f5dfc2..19e4356a3 100644
--- a/src/input_common.cpp
+++ b/src/input_common.cpp
@@ -2,7 +2,7 @@
 #include "config.h"
 
 #include <errno.h>
-#include <string.h>
+#include <cstring>
 #include <unistd.h>
 #ifdef HAVE_SYS_SELECT_H
 #include <sys/select.h>
@@ -205,7 +205,7 @@ wchar_t input_common_readch(int timed) {
 
             switch (sz) {
                 case (size_t)(-1): {
-                    memset(&state, '\0', sizeof(state));
+                    std::memset(&state, '\0', sizeof(state));
                     debug(2, L"Illegal input");
                     return R_NULL;
                 }
diff --git a/src/io.cpp b/src/io.cpp
index 5f2ed4166..727796c96 100644
--- a/src/io.cpp
+++ b/src/io.cpp
@@ -4,7 +4,7 @@
 #include <errno.h>
 #include <stddef.h>
 #include <stdio.h>
-#include <string.h>
+#include <cstring>
 #include <unistd.h>
 #include <cwchar>
 
diff --git a/src/iothread.cpp b/src/iothread.cpp
index a9d799b43..d3f7220dc 100644
--- a/src/iothread.cpp
+++ b/src/iothread.cpp
@@ -4,7 +4,7 @@
 #include <pthread.h>
 #include <signal.h>
 #include <stdio.h>
-#include <string.h>
+#include <cstring>
 #include <sys/select.h>
 #include <sys/time.h>
 #include <sys/types.h>
diff --git a/src/output.cpp b/src/output.cpp
index 5cca74258..14d210c3c 100644
--- a/src/output.cpp
+++ b/src/output.cpp
@@ -3,7 +3,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
+#include <cstring>
 #if HAVE_CURSES_H
 #include <curses.h>
 #elif HAVE_NCURSES_H
@@ -234,7 +234,7 @@ void outputter_t::set_color(rgb_color_t c, rgb_color_t c2) {
         if (c == c2) c = (c2 == rgb_color_t::white()) ? rgb_color_t::black() : rgb_color_t::white();
     }
 
-    if ((enter_bold_mode != 0) && (strlen(enter_bold_mode) > 0)) {
+    if ((enter_bold_mode != 0) && (std::strlen(enter_bold_mode) > 0)) {
         if (bg_set && !last_bg_set) {
             // Background color changed and is set, so we enter bold mode to make reading easier.
             // This means bold mode is _always_ on when the background color is set.
@@ -295,7 +295,7 @@ void outputter_t::set_color(rgb_color_t c, rgb_color_t c2) {
     }
 
     // Lastly, we set bold, underline, italics, dim, and reverse modes correctly.
-    if (is_bold && !was_bold && enter_bold_mode && strlen(enter_bold_mode) > 0 && !bg_set) {
+    if (is_bold && !was_bold && enter_bold_mode && std::strlen(enter_bold_mode) > 0 && !bg_set) {
         // The unconst cast is for NetBSD's benefit. DO NOT REMOVE!
         writembs_nofail(*this, tparm((char *)enter_bold_mode));
         was_bold = is_bold;
@@ -310,27 +310,27 @@ void outputter_t::set_color(rgb_color_t c, rgb_color_t c2) {
     }
     was_underline = is_underline;
 
-    if (was_italics && !is_italics && enter_italics_mode && strlen(enter_italics_mode) > 0) {
+    if (was_italics && !is_italics && enter_italics_mode && std::strlen(enter_italics_mode) > 0) {
         writembs_nofail(*this, exit_italics_mode);
         was_italics = is_italics;
     }
 
-    if (!was_italics && is_italics && enter_italics_mode && strlen(enter_italics_mode) > 0) {
+    if (!was_italics && is_italics && enter_italics_mode && std::strlen(enter_italics_mode) > 0) {
         writembs_nofail(*this, enter_italics_mode);
         was_italics = is_italics;
     }
 
-    if (is_dim && !was_dim && enter_dim_mode && strlen(enter_dim_mode) > 0) {
+    if (is_dim && !was_dim && enter_dim_mode && std::strlen(enter_dim_mode) > 0) {
         writembs_nofail(*this, enter_dim_mode);
         was_dim = is_dim;
     }
 
     if (is_reverse && !was_reverse) {
         // Some terms do not have a reverse mode set, so standout mode is a fallback.
-        if (enter_reverse_mode && strlen(enter_reverse_mode) > 0) {
+        if (enter_reverse_mode && std::strlen(enter_reverse_mode) > 0) {
             writembs_nofail(*this, enter_reverse_mode);
             was_reverse = is_reverse;
-        } else if (enter_standout_mode && strlen(enter_standout_mode) > 0) {
+        } else if (enter_standout_mode && std::strlen(enter_standout_mode) > 0) {
             writembs_nofail(*this, enter_standout_mode);
             was_reverse = is_reverse;
         }
diff --git a/src/output.h b/src/output.h
index b0548aeb1..dee1ad982 100644
--- a/src/output.h
+++ b/src/output.h
@@ -69,7 +69,7 @@ class outputter_t {
     }
 
     /// Write a narrow NUL-terminated string.
-    void writestr(const char *str) { writestr(str, strlen(str)); }
+    void writestr(const char *str) { writestr(str, std::strlen(str)); }
 
     /// Write a narrow character.
     void push_back(char c) {
diff --git a/src/path.cpp b/src/path.cpp
index 2523e4ef9..93d941204 100644
--- a/src/path.cpp
+++ b/src/path.cpp
@@ -4,7 +4,7 @@
 #include "config.h"  // IWYU pragma: keep
 
 #include <errno.h>
-#include <string.h>
+#include <cstring>
 #include <sys/stat.h>
 #include <unistd.h>
 #include <cwchar>
@@ -272,7 +272,7 @@ static void maybe_issue_path_warning(const wcstring &which_dir, const wcstring &
         const wchar_t *env_var = using_xdg ? xdg_var.c_str() : L"HOME";
         debug(0, _(L"Unable to locate %ls directory derived from $%ls: '%ls'."), which_dir.c_str(),
               env_var, path.c_str());
-        debug(0, _(L"The error was '%s'."), strerror(saved_errno));
+        debug(0, _(L"The error was '%s'."), std::strerror(saved_errno));
         debug(0, _(L"Please set $%ls to a directory where you have write access."), env_var);
     }
     ignore_result(write(STDERR_FILENO, "\n", 1));
diff --git a/src/postfork.cpp b/src/postfork.cpp
index ca3607628..f4c14b6b6 100644
--- a/src/postfork.cpp
+++ b/src/postfork.cpp
@@ -5,7 +5,7 @@
 #include <fcntl.h>
 #include <signal.h>
 #include <stdio.h>
-#include <string.h>
+#include <cstring>
 #include <time.h>
 #include <memory>
 #if FISH_USE_POSIX_SPAWN
@@ -308,11 +308,11 @@ void safe_report_exec_error(int err, const char *actual_cmd, const char *const *
             size_t sz = 0;
             const char *const *p;
             for (p = argv; *p; p++) {
-                sz += strlen(*p) + 1;
+                sz += std::strlen(*p) + 1;
             }
 
             for (p = envv; *p; p++) {
-                sz += strlen(*p) + 1;
+                sz += std::strlen(*p) + 1;
             }
 
             format_size_safe(sz1, sz);
diff --git a/src/print_help.cpp b/src/print_help.cpp
index c19a51dfc..db8ed074b 100644
--- a/src/print_help.cpp
+++ b/src/print_help.cpp
@@ -3,7 +3,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
+#include <cstring>
 
 #include "common.h"
 #include "print_help.h"
@@ -17,6 +17,6 @@ void print_help(const char *c, int fd) {
     int printed = snprintf(cmd, CMD_LEN, "fish -c '__fish_print_help %s >&%d'", c, fd);
 
     if (printed < CMD_LEN && system(cmd) == -1) {
-        write_loop(2, HELP_ERR, strlen(HELP_ERR));
+        write_loop(2, HELP_ERR, std::strlen(HELP_ERR));
     }
 }
diff --git a/src/reader.cpp b/src/reader.cpp
index 505dae066..0b8861633 100644
--- a/src/reader.cpp
+++ b/src/reader.cpp
@@ -23,7 +23,7 @@
 #include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
+#include <cstring>
 #ifdef HAVE_SYS_SELECT_H
 #include <sys/select.h>
 #endif
@@ -969,13 +969,13 @@ void reader_init() {
     tcgetattr(STDIN_FILENO, &terminal_mode_on_startup);
 
     // Set the mode used for program execution, initialized to the current mode.
-    memcpy(&tty_modes_for_external_cmds, &terminal_mode_on_startup,
+    std::memcpy(&tty_modes_for_external_cmds, &terminal_mode_on_startup,
            sizeof tty_modes_for_external_cmds);
     tty_modes_for_external_cmds.c_iflag &= ~IXON;   // disable flow control
     tty_modes_for_external_cmds.c_iflag &= ~IXOFF;  // disable flow control
 
     // Set the mode used for the terminal, initialized to the current mode.
-    memcpy(&shell_modes, &terminal_mode_on_startup, sizeof shell_modes);
+    std::memcpy(&shell_modes, &terminal_mode_on_startup, sizeof shell_modes);
 
     shell_modes.c_iflag &= ~ICRNL;  // disable mapping CR (\cM) to NL (\cJ)
     shell_modes.c_iflag &= ~INLCR;  // disable mapping NL (\cJ) to CR (\cM)
@@ -2447,7 +2447,7 @@ maybe_t<wcstring> reader_data_t::readline(int nchars) {
                                                      (size_t)READAHEAD_MAX)
                                           : READAHEAD_MAX;
 
-                memset(arr, 0, sizeof(arr));
+                std::memset(arr, 0, sizeof(arr));
                 arr[0] = c;
 
                 for (i = 1; i < limit; ++i) {
diff --git a/src/screen.cpp b/src/screen.cpp
index bc3161a40..30efe600f 100644
--- a/src/screen.cpp
+++ b/src/screen.cpp
@@ -10,7 +10,7 @@
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
+#include <cstring>
 #include <time.h>
 #include <unistd.h>
 #include <cwchar>
@@ -460,7 +460,7 @@ static void s_move(screen_t *s, int new_x, int new_y) {
 
     y_steps = new_y - s->actual.cursor.y;
 
-    if (y_steps > 0 && (strcmp(cursor_down, "\n") == 0)) {
+    if (y_steps > 0 && (std::strcmp(cursor_down, "\n") == 0)) {
         // This is very strange - it seems some (all?) consoles use a simple newline as the cursor
         // down escape. This will of course move the cursor to the beginning of the line as well as
         // moving it down one step. The cursor_up does not have this behaviour...
@@ -496,7 +496,7 @@ static void s_move(screen_t *s, int new_x, int new_y) {
     // Use the bulk ('multi') output for cursor movement if it is supported and it would be shorter
     // Note that this is required to avoid some visual glitches in iTerm (issue #1448).
     bool use_multi =
-        multi_str != NULL && multi_str[0] != '\0' && abs(x_steps) * strlen(str) > strlen(multi_str);
+        multi_str != NULL && multi_str[0] != '\0' && abs(x_steps) * std::strlen(str) > std::strlen(multi_str);
     if (use_multi && cur_term) {
         char *multi_param = tparm((char *)multi_str, abs(x_steps));
         writembs(outp, multi_param);
diff --git a/src/tinyexpr.cpp b/src/tinyexpr.cpp
index 842219dea..e4ae70a34 100644
--- a/src/tinyexpr.cpp
+++ b/src/tinyexpr.cpp
@@ -26,7 +26,7 @@
 #include "tinyexpr.h"
 #include <stdlib.h>
 #include <math.h>
-#include <string.h>
+#include <cstring>
 #include <stdio.h>
 #include <limits.h>
 
@@ -96,9 +96,9 @@ static te_expr *new_expr(const int type, const te_expr *parameters[]) {
     te_expr *ret = (te_expr *)malloc(size);
     // This sets float to 0, which depends on the implementation.
     // We rely on IEEE-754 floats anyway, so it's okay.
-    memset(ret, 0, size);
+    std::memset(ret, 0, size);
     if (arity && parameters) {
-        memcpy(ret->parameters, parameters, psize);
+        std::memcpy(ret->parameters, parameters, psize);
     }
     ret->type = type;
     return ret;
@@ -192,10 +192,10 @@ static const te_builtin *find_builtin(const char *name, int len) {
     const te_builtin *found = std::lower_bound(std::begin(functions), end, name,
                                                 [len](const te_builtin &lhs, const char *rhs) {
                                                     // The length is important because that's where the parens start
-                                                    return strncmp(lhs.name, rhs, len) < 0;
+                                                    return std::strncmp(lhs.name, rhs, len) < 0;
                                                 });
     // We need to compare again because we might have gotten the first "larger" element.
-    if (found != end && strncmp(found->name, name, len) == 0) return found;
+    if (found != end && std::strncmp(found->name, name, len) == 0) return found;
     return NULL;
 }
 
diff --git a/src/wgetopt.cpp b/src/wgetopt.cpp
index 2355db669..c39ccd730 100644
--- a/src/wgetopt.cpp
+++ b/src/wgetopt.cpp
@@ -40,7 +40,7 @@
 
 #include <stdio.h>
 #include <cwchar>
-#include <string.h>
+#include <cstring>
 
 // This version of `getopt' appears to the caller like standard Unix `getopt' but it behaves
 // differently for the user, since it allows the user to intersperse the options with the other
diff --git a/src/wutil.cpp b/src/wutil.cpp
index b9aefb108..2004dcf42 100644
--- a/src/wutil.cpp
+++ b/src/wutil.cpp
@@ -10,7 +10,7 @@
 #include <pthread.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
+#include <cstring>
 #include <sys/stat.h>
 #if defined(__linux__)
 #include <sys/statfs.h>
@@ -130,7 +130,7 @@ const wcstring wgetcwd() {
         return str2wcstring(res);
     }
 
-    debug(0, _(L"getcwd() failed with errno %d/%s"), errno, strerror(errno));
+    debug(0, _(L"getcwd() failed with errno %d/%s"), errno, std::strerror(errno));
     return wcstring();
 }
 
@@ -262,7 +262,7 @@ void wperror(const wchar_t *s) {
     if (s[0] != L'\0') {
         std::fwprintf(stderr, L"%ls: ", s);
     }
-    std::fwprintf(stderr, L"%s\n", strerror(e));
+    std::fwprintf(stderr, L"%s\n", std::strerror(e));
 }
 
 int make_fd_nonblocking(int fd) {
@@ -318,7 +318,7 @@ int fd_check_is_remote(int fd) {
 }
 
 static inline void safe_append(char *buffer, const char *s, size_t buffsize) {
-    strncat(buffer, s, buffsize - strlen(buffer) - 1);
+    std::strncat(buffer, s, buffsize - std::strlen(buffer) - 1);
 }
 
 // In general, strerror is not async-safe, and therefore we cannot use it directly. So instead we
@@ -328,7 +328,7 @@ const char *safe_strerror(int err) {
 #if defined(__UCLIBC__)
     // uClibc does not have sys_errlist, however, its strerror is believed to be async-safe.
     // See issue #808.
-    return strerror(err);
+    return std::strerror(err);
 #elif defined(HAVE__SYS__ERRS) || defined(HAVE_SYS_ERRLIST)
 #ifdef HAVE_SYS_ERRLIST
     if (err >= 0 && err < sys_nerr && sys_errlist[err] != NULL) {
@@ -373,7 +373,7 @@ void safe_perror(const char *message) {
     safe_append(buff, safe_strerror(err), sizeof buff);
     safe_append(buff, "\n", sizeof buff);
 
-    ignore_result(write(STDERR_FILENO, buff, strlen(buff)));
+    ignore_result(write(STDERR_FILENO, buff, std::strlen(buff)));
     errno = err;
 }
 
diff --git a/src/wutil.h b/src/wutil.h
index 661e82d05..80eaf8005 100644
--- a/src/wutil.h
+++ b/src/wutil.h
@@ -59,7 +59,7 @@ void wperror(const wchar_t *s);
 /// Async-safe version of perror().
 void safe_perror(const char *message);
 
-/// Async-safe version of strerror().
+/// Async-safe version of std::strerror().
 const char *safe_strerror(int err);
 
 /// Wide character version of getcwd().