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:

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    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

---

Second call is to a different function (ends in Ex) - see the return type for that function: SetFilePointerEx function (Windows)

gg

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

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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.

Quote:

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Originally Posted by MutantJohn

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

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