strcpy_s, wcscpy_s, _mbscpy_s

Copies a string. These versions of strcpy, wcscpy, _mbscpy have security enhancements, as described in Security Features in the CRT.


_mbscpy_s cannot be used in applications that execute in the Windows Runtime. For more information, see CRT functions not supported in Universal Windows Platform apps.


errno_t strcpy_s(
   char *dest,
   rsize_t dest_size,
   const char *src
errno_t wcscpy_s(
   wchar_t *dest,
   rsize_t dest_size,
   const wchar_t *src
errno_t _mbscpy_s(
   unsigned char *dest,
   rsize_t dest_size,
   const unsigned char *src
// Template functions are C++ only:
template <size_t size>
errno_t strcpy_s(
   char (&dest)[size],
   const char *src
); // C++ only
template <size_t size>
errno_t wcscpy_s(
   wchar_t (&dest)[size],
   const wchar_t *src
); // C++ only
template <size_t size>
errno_t _mbscpy_s(
   unsigned char (&dest)[size],
   const unsigned char *src
); // C++ only


Location of the destination string buffer.

Size of the destination string buffer in char units for narrow and multi-byte functions, and wchar_t units for wide functions. This value must be greater than zero and not greater than RSIZE_MAX.

Null-terminated source string buffer.

Return Value

Zero if successful; otherwise, an error.

Error Conditions

dest dest_size src Return value Contents of dest
NULL any any EINVAL not modified
any any NULL EINVAL dest[0] set to 0
any 0, or too small any ERANGE dest[0] set to 0


The strcpy_s function copies the contents in the address of src, including the terminating null character, to the location that's specified by dest. The destination string must be large enough to hold the source string and its terminating null character. The behavior of strcpy_s is undefined if the source and destination strings overlap.

wcscpy_s is the wide-character version of strcpy_s, and _mbscpy_s is the multibyte-character version. The arguments of wcscpy_s are wide-character strings; those of _mbscpy_s are multibyte-character strings. These three functions behave identically otherwise.

If dest or src is a null pointer, or if the destination string size dest_size is too small, the invalid parameter handler is invoked, as described in Parameter Validation. If execution is allowed to continue, these functions return EINVAL and set errno to EINVAL when dest or src is a null pointer, and they return ERANGE and set errno to ERANGE when the destination string is too small.

Upon successful execution, the destination string is always null-terminated.

In C++, use of these functions is simplified by template overloads that can infer buffer length automatically so that you don't have to specify a size argument, and they can automatically replace older, less-secure functions with their newer, more secure counterparts. For more information, see Secure Template Overloads.

The debug library versions of these functions first fill the buffer with 0xFE. To disable this behavior, use _CrtSetDebugFillThreshold.

Generic-Text Routine Mappings

TCHAR.H routine _UNICODE & _MBCS not defined _MBCS defined _UNICODE defined
_tcscpy_s strcpy_s _mbscpy_s wcscpy_s


Routine Required header
strcpy_s <string.h>
wcscpy_s <string.h> or <wchar.h>
_mbscpy_s <mbstring.h>

These functions are Microsoft-specific. For additional compatibility information, see Compatibility.


Unlike production quality code, this sample calls the secure string functions without checking for errors:

// crt_strcpy_s.c
// Compile by using: cl /W4 crt_strcpy_s.c
// This program uses strcpy_s and strcat_s
// to build a phrase.

#include <string.h>     // for strcpy_s, strcat_s
#include <stdlib.h>     // for _countof
#include <stdio.h>      // for printf
#include <errno.h>      // for return values

int main(void)
    char string[80];

    strcpy_s(string, _countof(string), "Hello world from ");
    strcat_s(string, _countof(string), "strcpy_s ");
    strcat_s(string, _countof(string), "and ");
    strcat_s(string, _countof(string), "strcat_s!");

    printf("String = %s\n", string);
String = Hello world from strcpy_s and strcat_s!

When building C++ code, the template versions may be easier to use.

// crt_wcscpy_s.cpp
// Compile by using: cl /EHsc /W4 crt_wcscpy_s.cpp
// This program uses wcscpy_s and wcscat_s
// to build a phrase.

#include <cstring>  // for wcscpy_s, wcscat_s
#include <cstdlib>  // for _countof
#include <iostream> // for cout, includes <cstdlib>, <cstring>
#include <errno.h>  // for return values

int main(void)
    wchar_t string[80];
    // using template versions of wcscpy_s and wcscat_s:
    wcscpy_s(string, L"Hello world from ");
    wcscat_s(string, L"wcscpy_s ");
    wcscat_s(string, L"and ");
    // of course we can supply the size explicitly if we want to:
    wcscat_s(string, _countof(string), L"wcscat_s!");

    std::wcout << L"String = " << string << std::endl;
String = Hello world from wcscpy_s and wcscat_s!

See also

String Manipulation
strcat, wcscat, _mbscat
strcmp, wcscmp, _mbscmp
strncat_s, _strncat_s_l, wcsncat_s, _wcsncat_s_l, _mbsncat_s, _mbsncat_s_l
strncmp, wcsncmp, _mbsncmp, _mbsncmp_l
strncpy_s, _strncpy_s_l, wcsncpy_s, _wcsncpy_s_l, _mbsncpy_s, _mbsncpy_s_l
_strnicmp, _wcsnicmp, _mbsnicmp, _strnicmp_l, _wcsnicmp_l, _mbsnicmp_l
strrchr, wcsrchr, _mbsrchr, _mbsrchr_l
strspn, wcsspn, _mbsspn, _mbsspn_l