c++ cant use functions of .h header file

Question

suddenly i couldnt use the new function i wrote which in .h header file and the old functions which i wrote i can use it, i cant believe that :S

stdafx.h

#include "function.h"

Hook.h

#include "stdafx.h"

    namespace DragoN_Hook
    {
            void EditOrginalCastleWar(int StartHour,int EndHour){

            unsigned char lol[4] = {0x83, 0x7A, 0x08,(unsigned char)StartHour};
            MemoryCopy((DWORD)0x00411A05,(DWORD)&lol,4);

    }
}

function.h

LPVOID MemoryCopy(DWORD destination, DWORD source, int length);

function.cpp

LPVOID MemoryCopy(DWORD destination, DWORD source, int length)
{
    DWORD oldSource      = 0;
    DWORD oldDestination = 0;

    VirtualProtect((LPVOID)source,length,PAGE_EXECUTE_READWRITE,&oldSource);
    VirtualProtect((LPVOID)destination,length,PAGE_EXECUTE_READWRITE,&oldDestination);

    memcpy((void*)destination,(void*)source,length);

    VirtualProtect((LPVOID)destination,length,oldDestination,&oldDestination);
    VirtualProtect((LPVOID)source,length,oldSource,&oldSource);

    return (LPVOID)destination;
};

Error *error C3861: 'MemoryCopy': identifier not found*

Answer 1

This happens usually when you compile and individual file which does not cause the precomplied header to be rebuilt. If you rebuild the solution it will recreate the header. You can also turn off precompled headers and not have to deal with it.