Copies a block of memory from one location to another.

Syntax

void CopyMemory(
  __in  PVOID Destination,
  __in  const VOID *Source,
  __in  SIZE_T Length
);

Parameters

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.

Remarks

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.

Examples

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);
}

Requirements

See Also

FillMemory

Memory Management Functions

MoveMemory

SecureZeroMemory

ZeroMemory

Send comments about this topic to Microsoft

Build date: 9/17/2009