Worst programmer ever?

So I wrote a function to copy a specified number of bytes
from one stream to another:

void vCopyFile(FILE *fIn, FILE *fOut, int iNum) {
    while (iNum--)
        (void)fputc(fgetc(fIn), fOut);
}

I was told the following:
20:34:53 < dinesh> wow
20:35:00 < dinesh> probably one of the worst function i ever saw

So I changed it to this:

void vCopyFile(FILE *fIn, FILE *fOut, int iNum) {
    char *cBuf = (char*)malloc(iNum);
    int iRead;

    iRead = fread(cBuf, 1, iNum, fIn);
    fwrite(cBuf, 1, iRead, fOut);
}

Both functions work on Linux but seem to skip bytes when
crosscompiled with mingw32-gcc or visual studio.

What am I doing wrong?

void copy(InputStream in, OutputStream out, int num, int bufSize) throws IOException {
    byte[] buf = new byte[bufSize];
    int n;
    while (num > 0 && (n = in.read(buf, 0, num < bufSize ? num : bufSize)) >= 0) {
        out.write(buf, 0, n);
        num -= n;
    }
}