File reading in C/C++ common for Linux and Windows

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C++

C

Linux

VC9.0

To read binary data from a file, I have written a code as follows,

int fd = open(sFilePath, O_RDONLY, 0); //BINARY READ OPERATION
int iBytesToRead = 100;
unsigned char* pBuffer = new unsigned char[iBytesToRead];
while(true)
{
    int iReadBytes = read(fd, pBuffer, iBytesToRead);
    if( !iReadBytes ) break;
}

In Windows (VC9), within 'while' loop, first time it 'read()' returns '63' whatever value (more than 63!) is passed in 'iBytesToRead'. And later on it returns '0' (break from the loop).
But file size is much more than that, as same code for same file works properly in Linux (gcc).

Is there any wrong in this or Am I missing something in it?

Thanks & Regards,
Aniket A. Salunkhe