#include <stdio.h>
char *strcpy(char *dst, const char *src);
char *strncpy(char *dst, const char *src, size_t n);

#define __STDC_WANT_LIB_EXT1__ 1
#include <stdio.h>
errno_t strcpy_s(char *dst, rsize_t dstmax, const char *src);
errno_t strncpy_s(char *dst, rsize_t dstmax, const char *src, rsize_t n);

#include <wchar.h>
wchar_t *wcscpy(wchar_t *dst, const wchar_t *src);
wchar_t *wcsncpy(wchar_t *dst, const wchar_t *src, size_t n);

#define __STDC_WANT_LIB_EXT1__ 1
#include <wchar.h>
errno_t wcscpy_s(wchar_t *dst, rsize_t dstmax, const wchar_t *src);
errno_t wcsncpy_s(wchar_t *dst, rsize_t dstmax, const wchar_t *src, rsize_t n);

The strcpy family of functions copy a null-terminated string from src to an array dst, including the null terminator.

The functions with a parameter n copy at most n characters, so their src strings need not be null-terminated, and the result in dst might not be null-terminated. They also continue write exactly n characters by padding with nulls.

The _s variants fail if more than dstmax characters would have to be copied, or if dstmax or n is greater than RSIZE_MAX, returning non-zero. They also ensure that a null character terminates the result in dst, and place it at the start when failing. The other functions return dst.

#include <stdio.h>
char *strcat(char *dst, const char *src);
char *strncat(char *dst, const char *src, size_t n);

#define __STDC_WANT_LIB_EXT1__ 1
#include <stdio.h>
errno_t strcat_s(char *dst, rsize_t dstmax, const char *src);
errno_t strncat_s(char *dst, rsize_t dstmax, const char *src, rsize_t n);

#include <wchar.h>
wchar_t *wcscat(wchar_t *dst, const wchar_t *src);
wchar_t *wcsncat(wchar_t *dst, const wchar_t *src, size_t n);

#define __STDC_WANT_LIB_EXT1__ 1
#include <wchar.h>
errno_t wcscat_s(wchar_t *dst, rsize_t dstmax, const wchar_t *src);
errno_t wcsncat_s(wchar_t *dst, rsize_t dstmax, const wchar_t *src, rsize_t n);

The strcat family of functions do the same as their counterparts in the strcpy family, except that dst must be a null-terminated string on input. These functions find the null terminator, and then perform a copy starting at that point, overwriting the original null terminator, thereby appending the string src onto the end of string dst. dstmax is reduced to account for the string already present in dst.