c - Problems using fread() on stdin under win32

Question

I'm trying to parse data from stdin in binary mode under Win32. The first thing my code does is to check for a 4byte header at the beginning:

int riff_header;
fread(&riff_header, sizeof(riff_header), 1, ifp);
//  'RIFF' = little-endian
if (riff_header != 0x46464952) {
    fprintf(stderr, "wav2msu: Incorrect header: Invalid format or endianness
");
    fprintf(stderr, "         Value was: 0x%x
", riff_header);
    return -1;
}

stdin has been switched to binary mode before reading from it:

if (*argv[argc-1] == '-') {
    fprintf(stderr, "Reading from stdin.
");
    infile = stdin;
    // We need to switch stdin to binary mode, or else we run
    // into problems under Windows
    freopen(NULL, "rb", stdin);
}

This code works fine under Linux, however on Win32 (specifically Windows XP), the fread only seems to read a single byte and thus cause the evaluation to fail. Example:

> ffmeg.exe -i ..est.mp3 -f wav pipe:1 2> nul |..foo.exe -o test.bin -
Reading from stdin.
foo: Incorrect header: Invalid format or endianness
     Value was: 0x4

What am I doing wrong?

Answer 1

According to the MSDN documentation, it's not permitted to pass NULL for the path parameter of freopen, so the call to freopen is almost certainly failing; have you checked the return value and the value of errno? C89 does not specify the behavior of freopen when path is NULL; C99 does, but the Microsoft C runtime is not (and does not claim to be) C99-compliant.

If you really need to read binary info from stdin, you might have to use platform-specific code and read the raw binary data directly with ReadFile on the file GetStdHandle(STD_INPUT_HANDLE).