ReadFile() and SetFilePointer Problems?

This is a discussion on ReadFile() and SetFilePointer Problems? within the C++ Programming forums, part of the General Programming Boards category; Hii In my program I'm reading the clusters in the volume using the appropriate physical offsets to the disk. Code: ...

  1. #1
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    ReadFile() and SetFilePointer Problems?

    Hii

    In my program I'm reading the clusters in the volume using the appropriate physical offsets to the disk.



    Code:
    for(  i=0; i<  total_number_ of_ clusters;i++)
    {
      
    // convert logical offset to physical offset 
    
     phys_offset= conversion(i);  // this value I get correctly
    
    
     if(!SetFilePointer(drive_handle, 
                                 phys_offset,
                                 NULL,
                                 0))
    {
     printf("\nSetFilePointer Failed: Error Number : %d\n",GetLastError());
     return o;
     }
    
    
     if(!ReadFile(drive_handle,
                        bBuffer1,
                        cluster_size,
                        &dwRetBytes1,
                        0))
    {
    printf("\nUnable to Read the Drive Error: %d\n",GetLastError());   
    return o;
    }
       
    
    } // next cluster

    The above code not giving no error messages, but how do we know the program reading correctly?
    It returns the correct no of bytes read after one read operation .
    When I wrote theses data into destination , nothing wrote.

    What may be the problem??
    Where is the mistake in the code ?


    Any idea?
    -----------
    Thanking you
    Krish

  2. #2
    Guest Sebastiani's Avatar
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    Well then if the above code is working properly, why not post the part where you actually attempted to write it somewhere?
    Code:
    #include <cmath>
    #include <complex>
    bool flip(bool value)
    {
           return std::pow
        (
            std::complex<float>(std::exp(1.0)), 
            std::complex<float>(0, 1) * std::complex<float>(std::atan(1.0)*(1 << (value + 2)))
        ).real() < 0;
    }

  3. #3
    Guest Sebastiani's Avatar
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    According to MSDN docs, SetFilePointer doesn't return a boolean (and in fact, returns 0xFFFFFFFF on error). Obviously, then, the function is failing in your code...
    Code:
    #include <cmath>
    #include <complex>
    bool flip(bool value)
    {
           return std::pow
        (
            std::complex<float>(std::exp(1.0)), 
            std::complex<float>(0, 1) * std::complex<float>(std::atan(1.0)*(1 << (value + 2)))
        ).real() < 0;
    }

  4. #4
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    I mean no compilation and link errors.. the code is doesn't give correct result I want.

  5. #5
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    Mr...

    You are correct....I corrected my code as below

    Code:
      DWORD dwPtr1=SetFilePointer(drive_handle,phys_offset,NULL,0);
           if (dwPtr1 == INVALID_SET_FILE_POINTER) // Test for failure
    	   {
    	   printf("\nSetFilePointer Failed to write,Err No:%d\n",GetLastError());
    	   goto  label12;
    	   }

  6. #6
    Guest Sebastiani's Avatar
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    >> You are correct....I corrected my code as below

    So...everything is working properly then??

    >> SetFilePointer(drive_handle,phys_offset,NULL,0)

    The last parameter should be FILE_BEGIN, FILE_CURRENT, or FILE_END. Using 0 is not portable,and obscures the meaning.
    Code:
    #include <cmath>
    #include <complex>
    bool flip(bool value)
    {
           return std::pow
        (
            std::complex<float>(std::exp(1.0)), 
            std::complex<float>(0, 1) * std::complex<float>(std::atan(1.0)*(1 << (value + 2)))
        ).real() < 0;
    }

  7. #7
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    but I can't set the file pointer....to write the read data

    And my physical offsets are correct ,I verified them....


    the physical offset is 58070509056


    While using set pointer () the error occurs.



    ERROR_NEGATIVE_SEEK 131 0x83

    An attempt was made to move the file pointer before the beginning of the file.


    What may be the problem???

  8. #8
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    hiii

    Code:
    
        #define FILE_BEGIN           0
       #define FILE_CURRENT       1
       #define FILE_END                2
    
    
    // the above are defined in <winbase.h>
    

  9. #9
    Guest Sebastiani's Avatar
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    >> the physical offset is 58070509056

    A DWORD can only hold a value up to 4294967295. You'll probably need to use that 3rd parameter to SetFilePointer then, don't you think?

    >> // the above are defined in <winbase.h>

    There is nothing stopping the API from changing these values in future versions, so you should always stick with the pre-defined macros, for portability.
    Code:
    #include <cmath>
    #include <complex>
    bool flip(bool value)
    {
           return std::pow
        (
            std::complex<float>(std::exp(1.0)), 
            std::complex<float>(0, 1) * std::complex<float>(std::atan(1.0)*(1 << (value + 2)))
        ).real() < 0;
    }

  10. #10
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    If the function succeeds and lpDistanceToMoveHigh is NULL, the return value is the low-order DWORD of the new file pointer.

    DWORD WINAPI SetFilePointer(
    __in HANDLE hFile,
    __in LONG lDistanceToMove, //58070509056
    __inout_opt PLONG lpDistanceToMoveHigh, //NULL
    __in DWORD dwMoveMethod //FILE_BEGIN
    );


    The how it becomes an error code?

  11. #11
    Guest Sebastiani's Avatar
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    You need to read the reponses to your questions more carefully. I've already pointed this out to you, and so I am just repeating myself here:

    >> __in LONG lDistanceToMove, //58070509056

    OK, once again, you *cannot* fit that number into a 32 bit variable.

    >> The how it becomes an error code?

    It becomes an error code by being 0xffffffff.
    Code:
    #include <cmath>
    #include <complex>
    bool flip(bool value)
    {
           return std::pow
        (
            std::complex<float>(std::exp(1.0)), 
            std::complex<float>(0, 1) * std::complex<float>(std::atan(1.0)*(1 << (value + 2)))
        ).real() < 0;
    }

  12. #12
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    I cleared my code as follows


    Code:
    DWORD dwPtr1=SetFilePointer(hDevice1,
                                                     li_offset2.LowPart,
                                                    &li_offset2.HighPart,
                                                    FILE_BEGIN);
    
    if (dwPtr1 == INVALID_SET_FILE_POINTER) // Test for failure
    {
    printf("\n\nSetFilePointer Failed to write,Err No:%d\n",GetLastError());
    return 0;
    }

  13. #13
    and the hat of wrongness Salem's Avatar
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    There's something you're all missing.
    ReadFile() and SetFilePointer Problems? - C++

    The problem is the OP.
    They're just scattering fragments of the same question all over the place, but when they provide "new information", they neglect to tell everyone else about it as well.

    So pretty much everyone spends (read: wastes) their time wandering around in the dark.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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