memcpy-字节的int变量

Question

I am trying to create a data packet, using memcpy . I expect to see the output in pOutBuffer , whose first four bytes will have 999, followed by 111 followed by 12; But currently i am getting some garbage.

The problem is that instead of copying the value, it copies the address, I think. How can i copy these values in to a contiguous memory so that i can write it to disk and can retrieve the data at the receiving end with my defined format?

Thanks.

#include "stdafx.h"
#include "windows.h"
typedef struct
{
    int Begin;
    int End;
    int Size;
}PACKET;


void AddBuffer(PACKET* pPacket, BYTE* pOutBuffer)
{
    memcpy(pOutBuffer, &pPacket->Begin, sizeof(int));
    memcpy(pOutBuffer+sizeof(int), &pPacket->End, sizeof(int));
    memcpy(pOutBuffer+sizeof(int)+sizeof(int), &pPacket->Size, sizeof(int));
}

int _tmain(int argc, _TCHAR* argv[])
{
    PACKET* pPacket = new PACKET;
    pPacket->Begin = 999;
    pPacket->End   = 111;
    pPacket->Size  = 12;

    BYTE* pOutBuffer = new BYTE [pPacket->Size];
    AddBuffer(pPacket, pOutBuffer);

    //Write pOutBuffer on to the disk 
    //WriteFile(vhFileToWrite,(BYTE*)pOutBuffer,pPacket.Size,&vRetFileSize,NULL);

    //Delete pOutBuffer
    return 0;
}

Source sample has been updated. It now builds ok

Answer 1

Your code works correctly. On a little-endian machine with sizeof(int)==4, the number 999 will be stored as the four bytes 0xe7, 0x03, 0x00, 0x00.

You said you saw the character 'ç': That is because you are trying to view the array as a string, and ç has the character code 0xe7, which is indeed the first byte written. If you view it as an array (either using Visual Studio's memory view, or by typing pOutBuffer,12 in the watch window), you will see the correct byte values.