diff --git a/helper.h b/helper.h
new file mode 100644
index 0000000..add3d95
--- /dev/null
+++ b/helper.h
@@ -0,0 +1,25 @@
+/* --------------------------------------------------------------
+* File          : helper.h
+* Authors       : Aoran Zeng <ccmywish@qq.com>
+* Created on    : <2023-08-28>
+* Last modified : <2023-08-28>
+*
+* helper:
+*
+*   helper functions and macros
+* -------------------------------------------------------------*/
+
+#include <string.h>
+#include <stdlib.h>
+
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof(x[0]))
+
+char*
+xy_strjoin(const char* str1, const char* str2)
+{
+  size_t len = strlen(str1) + strlen(str2) + 1;
+  char* ret  = malloc(len);
+  strcat(ret, str1);
+  strcat(ret, str2);
+  return ret;
+}