UApiHook

// UApiHook.h:
//---------------------------------------------------------------------------
#ifndef UApiHookH
#define UApiHookH
//---------------------------------------------------------------------------
#include <windows.h>
//---------------------------------------------------------------------------
#pragma pack (push, 1)
typedef struct _far_jmp{
    BYTE  PushOp;
    PVOID PushArg;
    BYTE  RetOp;
} far_jmp, *pfar_jmp;
typedef struct _OldCode{
    USHORT One;
    ULONG  TWO;
} OldCode, *POldCode;
#pragma pack (pop)
//---------------------------------------------------------------------------
OldCode HookAPI(PVOID API, PVOID NewFunc);
void UnhookAPI(OldCode OldProc, PVOID API);
//---------------------------------------------------------------------------
#endif



// UApiHook.cpp:
//---------------------------------------------------------------------------
#pragma hdrstop
//---------------------------------------------------------------------------
#include "UApiHook.h"
//---------------------------------------------------------------------------
OldCode HookAPI(PVOID API, PVOID NewFunc)
{
    try
    {
        if(!(API && NewFunc))
        {
            OldCode __NULLCODE;
            memset(&__NULLCODE, NULL, sizeof(OldCode));
            return __NULLCODE;
        }
        far_jmp Fnjp;
        OldCode Old;

        DWORD dwOldProtect = 0;
        SIZE_T lpNumberOfBytesWritten = 0;
        VirtualProtect(API, sizeof(far_jmp), PAGE_EXECUTE_READWRITE, &dwOldProtect);
        ReadProcessMemory(INVALID_HANDLE_VALUE, API, &Old, sizeof(OldCode), NULL);

        Fnjp.PushOp  = 0x68;
        Fnjp.PushArg = NewFunc;
        Fnjp.RetOp   = 0xC3;

        if(API != NULL && NewFunc != NULL) WriteProcessMemory(INVALID_HANDLE_VALUE, API, &Fnjp, sizeof(far_jmp), &lpNumberOfBytesWritten);
        return Old;
    }
    catch(...){}
}
//---------------------------------------------------------------------------
void UnhookAPI(OldCode OldProc, PVOID API)
{
    try
    {
        if(API == NULL) return;
        DWORD dwOldProtect = 0;
        VirtualProtect(API, sizeof(OldCode), PAGE_EXECUTE_READWRITE, &dwOldProtect);
        WriteProcessMemory(INVALID_HANDLE_VALUE, API, &OldProc, sizeof(OldCode), NULL);
    }
    catch(...){}
}
//---------------------------------------------------------------------------
#pragma package(smart_init)