Read 'Binary' files with ReadFile WinAPI - c++

Question

When I try to open '.exe' files with ReadFile() Windows API, It's just return the 2 first character of file like : MZ
Here is my Code:
#define BUFFERSIZE 5000
VOID CALLBACK FileIOCompletionRoutine(
__in DWORD dwErrorCode,
__in DWORD dwNumberOfBytesTransfered,
__in LPOVERLAPPED lpOverlapped
);
VOID CALLBACK FileIOCompletionRoutine(
__in DWORD dwErrorCode,
__in DWORD dwNumberOfBytesTransfered,
__in LPOVERLAPPED lpOverlapped)
{
_tprintf(TEXT("Error code:\t%x\n"), dwErrorCode);
_tprintf(TEXT("Number of bytes:\t%x\n"), dwNumberOfBytesTransfered);
g_BytesTransferred = dwNumberOfBytesTransfered;
}
HANDLE hFile;
DWORD dwBytesRead = 0;
char ReadBuffer[BUFFERSIZE] = { 0 };
OVERLAPPED ol = { 0 };
hFile = CreateFile(fullFilePath.c_str(), // file to open
GENERIC_READ, // open for reading
FILE_SHARE_READ, // share for reading
NULL, // default security
OPEN_EXISTING, // existing file only
FILE_ATTRIBUTE_NORMAL | FILE_FLAG_OVERLAPPED, // normal file
NULL); // no attr. template
ReadFileEx(hFile, ReadBuffer, BUFFERSIZE - 1, &ol, FileIOCompletionRoutine);
When I print ReadBuffer It's just MZ(exe file).
But Using:
std::ifstream file(argv[1], std::ios::in | std::ios::binary);
It's work perfectly.
How Can I Read Binary files With ReadFile?

Answer 1

The problem is not with reading, the problem is with printing.
You're not showing your code, but you're likely trying to print with printf or something similar. IOW, you're printing it as C string.
Well, binary data includes 0s, and in this case the first 3 bytes are 'M', 'Z', '\0' - and that prints as a null-terminated string "MZ".
You'd have to write a converter to per-byte hex numbers if you want to see meaningful printing of binary data: 4D 5A 00 and so on

Answer 2

How Can I Read Binary files With ReadFile?
ReadFile (and ReadFileEx ) works 'in binary mode'. You get exact file contents byte by byte without any translation.
You have problem with writing/printing. This mostly depends where you want to write, but for outputing (binary) data potentially containing nulls in C++ choose write method
some_output_stream.write( buffer_ptr, num_bytes_in_buffer );
some_output_stream should be set to binary mode (std::ios::binary). Without this flag all bytes with value 10 could be translated to pairs 13,10.
If C FILE functions are used
fwrite( buffer_ptr, 1, num_bytes_in_buffer, some_output_file );
Again some_output_file has to be in binary mode.
In some scenarios WriteFile can be used complementary to your usage of ReadFile.