memcpy_s, wmemcpy_s

Copies bytes between buffers. These are versions of memcpy, wmemcpy with security enhancements as described in Security Features in the CRT.


errno_t memcpy_s(
   void *dest,
   size_t destSize,
   const void *src,
   size_t count
errno_t wmemcpy_s(
   wchar_t *dest,
   size_t destSize,
   const wchar_t *src,
   size_t count


New buffer.

Size of the destination buffer, in bytes for memcpy_s and wide characters (wchar_t) for wmemcpy_s.

Buffer to copy from.

Number of characters to copy.

Return Value

Zero if successful; an error code on failure.

Error Conditions

dest destSize src count Return value Contents of dest
any any any 0 0 Not modified
NULL any any non-zero EINVAL Not modified
any any NULL non-zero EINVAL dest is zeroed out
any < count any non-zero ERANGE dest is zeroed out


memcpy_s copies count bytes from src to dest; wmemcpy_s copies count wide characters (two bytes). If the source and destination overlap, the behavior of memcpy_s is undefined. Use memmove_s to handle overlapping regions.

These functions validate their parameters. If count is non-zero and dest or src is a null pointer, or destSize is smaller than count, these functions invoke the invalid parameter handler, as described in Parameter Validation. If execution is allowed to continue, these functions return EINVAL or ERANGE and set errno to the return value.

By default, this function's global state is scoped to the application. To change this, see Global state in the CRT.


Routine Required header
memcpy_s <memory.h> or <string.h>
wmemcpy_s <wchar.h>

For additional compatibility information, see Compatibility.


// crt_memcpy_s.c
// Copy memory in a more secure way.

#include <memory.h>
#include <stdio.h>

int main()
   int a1[10], a2[100], i;
   errno_t err;

   // Populate a2 with squares of integers
   for (i = 0; i < 100; i++)
      a2[i] = i*i;

   // Tell memcpy_s to copy 10 ints (40 bytes), giving
   // the size of the a1 array (also 40 bytes).
   err = memcpy_s(a1, sizeof(a1), a2, 10 * sizeof (int) );
   if (err)
      printf("Error executing memcpy_s.\n");
     for (i = 0; i < 10; i++)
       printf("%d ", a1[i]);
0 1 4 9 16 25 36 49 64 81

See also

Buffer Manipulation
memchr, wmemchr
memcmp, wmemcmp
memmove, wmemmove
memset, wmemset
strcpy, wcscpy, _mbscpy
strncpy, _strncpy_l, wcsncpy, _wcsncpy_l, _mbsncpy, _mbsncpy_l
strncpy_s, _strncpy_s_l, wcsncpy_s, _wcsncpy_s_l, _mbsncpy_s, _mbsncpy_s_l