ReadFileEx example - async read whole file

main.cpp

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

constexpr auto DWORD_size(){
    return sizeof(DWORD);
}

#define BUFZ 101

char buf[BUFZ];

HANDLE hstdout = GetStdHandle(STD_OUTPUT_HANDLE);

VOID LpoverlappedCompletionRoutine(
    DWORD dwErrorCode,
    DWORD dwNumberOfBytesTransfered,
    LPOVERLAPPED lpOverlapped){
    // printf("dwErrorCode=%d, dwNumberOfBytesTransfered=%d\n", dwErrorCode, dwNumberOfBytesTransfered);
    if (dwErrorCode | dwNumberOfBytesTransfered<=0){ 
        // maybe EOF reached?
    }else{
    constexpr auto size = DWORD_size();
    if constexpr (size==4)
        *((__int64*)&lpOverlapped->Offset) += dwNumberOfBytesTransfered;
    else if constexpr (size==8)
        *((__int128*)&lpOverlapped->Offset) += dwNumberOfBytesTransfered;
    else {
        abort();
    }
        WriteConsoleA(hstdout, buf, dwNumberOfBytesTransfered, NULL, NULL);
        if (ReadFileEx(lpOverlapped->hEvent, buf, sizeof(buf)-1, lpOverlapped, LpoverlappedCompletionRoutine)==FALSE){
            puts("ReadFileEx failed 2!");
       }
       SleepEx(100, TRUE);
    }
}

INT main(VOID)
{
    if (hstdout==NULL){
        puts("GetStdHandle failed!!");
        return 1;
    }
    OVERLAPPED ol {};
	   ol.hEvent = CreateFileA(__FILE__,
                       GENERIC_READ,
                       FILE_SHARE_READ,
                       NULL,
                       OPEN_EXISTING,    
                       FILE_ATTRIBUTE_NORMAL | FILE_FLAG_OVERLAPPED,
                       NULL);
       if (ol.hEvent==NULL){
            puts("CreateFileA failed!!");
            return 2;
       }
       if (ReadFileEx(ol.hEvent, buf, sizeof(buf)-1, &ol, LpoverlappedCompletionRoutine)==FALSE){
            puts("ReadFileEx failed!!");
            return 3;
       }
       SleepEx(INFINITE, TRUE); // need alertable wait to call async procedure, such as WSAaccept and SleepEx
}