memcpy_s, wmemcpy_s

Article
07/11/2012

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 numberOfElements,
   const void *src,
   size_t count 
);
errno_t wmemcpy_s(
   wchar_t *dest,
   size_t numberOfElements,
   const wchar_t *src,
   size_t count
);

Parameters

dest
New buffer.
numberOfElements
Size of the destination buffer.
src
Buffer to copy from.
count
Number of characters to copy.

Return Value

Zero if successful; an error code on failure.

Error Conditions

dest	numberOfElements	src	Return value	Contents of dest
NULL	any	any	EINVAL	not modified
any	any	NULL	EINVAL	dest is zeroed out
any	< count	any	ERANGE	dest is zeroed out

Remarks

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 dest or src is a null pointer, or numberOfElements is too small for the buffer, these functions invoke the invalid parameter handler, as described in Parameter Validation. If execution is allowed to continue, these functions return EINVAL and set errno to EINVAL.

Requirements

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

For additional compatibility information, see Compatibility in the Introduction.

Example

// 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");
   }
   else
   {
     for (i = 0; i < 10; i++)
       printf("%d ", a1[i]);
   }
   printf("\n");
}

0 1 4 9 16 25 36 49 64 81

.NET Framework Equivalent

Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.

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