Populating MultiByte Datatypes With Void Pointers To Unsigned Char's?

This is a discussion on Populating MultiByte Datatypes With Void Pointers To Unsigned Char's? within the C++ Programming forums, part of the General Programming Boards category; Im doing some binary datafile processing, and im reading the whole file in as a vector of unsigned bytes. If ...

  1. #1
    That Creepy Network Guy DeepBlackMagic's Avatar
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    Populating MultiByte Datatypes With Void Pointers To Unsigned Char's?

    Im doing some binary datafile processing, and im reading the whole file in as a vector of unsigned bytes. If i were to populate a 4 byte object like an unsigned int one byte at a time how would i go about it?

    Let me illustrate what im trying to do:
    Code:
    std::vector<unsigned char> FileContents; 
    //Assume i populate FileContents here, and its correctly filled. 
    unsigned int test; //4 bytes, i want to set the first byte to FileContents[5] and the second to [6] etc 
    
    //obviously this is incorrect, im just fishing for the correct way to do it. 
    void * TheVoid; 
    TheVoid = &test; 
    TheVoid[0] = *FileContents[5]; 
    TheVoid[1] = *FileContents[6];
    ...
    Does this make sense? Am i missing some critical thing that will make my life easier?

    Thanks for your time.

    .

  2. #2
    Guest Sebastiani's Avatar
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    Code:
    int i;
    char * p = (char*)&i;
    p[0] = fc[6];
    p[1] = fc[7];
    p[2] = fc[8];
    p[3] = fc[9];
    of course a much easier way to do it would be:

    Code:
    int i = *((int*)(&fc[6]));
    just keep in mind that the file needs to originate from a system with the same endian-ness as the program working with it, otherwise anything larger than a byte will be read incorrectly.

  3. #3
    That Creepy Network Guy DeepBlackMagic's Avatar
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    Thanks for the fast reply SEB, as always your a great help. Im trying to read in this ugly binary datafile and the refrence i have for it says field length is one size but it turns out to be another in a hex editor =( I loathe bad datatype refrences.

    Thanks again,

    DBM

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