Share via

CopyMemory function

Copies a block of memory from one location to another.


void CopyMemory(
  _In_       PVOID  Destination,
  _In_ const VOID   *Source,
  _In_       SIZE_T Length


  • Destination [in]
    A pointer to the starting address of the copied block's destination.

  • Source [in]
    A pointer to the starting address of the block of memory to copy.

  • Length [in]
    The size of the block of memory to copy, in bytes.

Return value

This function has no return value.


This function is defined as the RtlCopyMemory function. Its implementation is provided inline. For more information, see WinBase.h and WinNT.h.

If the source and destination blocks overlap, the results are undefined. For overlapped blocks, use the MoveMemory function.

Security Remarks

The first parameter, Destination, must be large enough to hold Length bytes of Source; otherwise, a buffer overrun may occur. This may lead to a denial of service attack against the application if an access violation occurs or, in the worst case, allow an attacker to inject executable code into your process. This is especially true if Destination is a stack-based buffer. Be aware that the last parameter, Length, is the number of bytes to copy into Destination, not the size of the Destination.


The following code example shows a safer way to use CopyMemory. Alternatively, you could use the memcpy_s or wmemcpy_s function.

#include <windows.h>
#include <tchar.h>
#include <stdio.h>

#define BUFFER_SIZE 1024
#define COPY_SIZE 512

   MyCopyMemory - A wrapper for CopyMemory

   buf     - destination buffer
   pbData  - source buffer
   cbData  - size of block to copy, in bytes
   bufsize - size of the destination buffer

void MyCopyMemory(TCHAR *buf, TCHAR *pbData, SIZE_T cbData, SIZE_T bufsize) 
    CopyMemory(buf, pbData, min(cbData,bufsize));

void main()
    TCHAR buf[BUFFER_SIZE] = TEXT("This is the destination");
    TCHAR pbData[BUFFER_SIZE] = TEXT("This is the source");

    MyCopyMemory(buf, pbData, COPY_SIZE*sizeof(TCHAR), BUFFER_SIZE*sizeof(TCHAR));

    _tprintf(TEXT("Destination buffer contents: %s\n"), buf);


Minimum supported client

Windows XP [desktop apps only]

Minimum supported server

Windows Server 2003 [desktop apps only]


WinBase.h (include Windows.h)



See also


Memory Management Functions