Thread: C++ - Trying to use SetFilePointer & SetFilePointerEx to read USB device

Hello,

Windows 10
gcc 5.3.0

I'm opening a USB memory stick for read.
I can read the beginning of the stick ok, then I try to reset
the file pointer to another position and fail.
What am I doing wrong?
Thanks.

Regards

Code:

    DWORD dwCurrentFilePosition = SetFilePointer(
                hdisk, // must have GENERIC_READ and/or GENERIC_WRITE
                0,     // do not move pointer
                NULL,  // hdisk is not large enough in needing this pointer
                FILE_CURRENT); // provides offset from current position
    printf("Current file pointer position: %lu\n", dwCurrentFilePosition);

Code:

    // position is a LARGE_INTEGER
    position.QuadPart = (__int64)1024;
    printf("LowPart:%lu HighPart:%lu\n", position.LowPart, position.HighPart);

    dwCurrentFilePosition = SetFilePointerEx(
                hdisk,    // must have GENERIC_READ and/or GENERIC_WRITE
                position, // new position
                NULL,     // hdisk is not large enough to need this pointer
                FILE_CURRENT); //provides offset from current position
    printf("New file pointer position: %lu\n", dwCurrentFilePosition);

Code:

Current file pointer position: 512 // this is correct, from previous read
LowPart:1024 HighPart:0
New file pointer position: 1 // should be 1024

Hello Codeplug,

Thanks for that.
Reverted to the original method.

Regards

Code:

int newPos = 2048; 

dwCurrentFilePosition = SetFilePointer(
     hdisk, //must have GENERIC_READ and/or GENERIC_WRITE 
     newPos - dwCurrentFilePosition, //relative to current pointer
     NULL, //hdisk is not large enough to need this pointer      
     FILE_CURRENT); //provides offset from current position
printf("Newfilepointerposition: %lu\n", dwCurrentFilePosition);

Code:

New file pointer position: 2048

Using cl.exe is, like, the most fun part of Windows development though :P

You'd be surprised at how loose gcc is with automatic conversions. cl.exe is actually pretty stringent.

Originally Posted by MutantJohn

You'd be surprised at how loose gcc is with automatic conversions. cl.exe is actually pretty stringent.

Is it possible that cl defaults to C++ mode? That would make it more stringent!