Thread: bmp files

  1. #1
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    bmp files

    i have a bmp file; i declared some structures

    Code:
    struct bmp_fileheader
    
    {...}
    I read the information:
    Code:
    struct bmp_fileheader prim;
    fread(&prim, sizeof(prim), image);
    but now i have to write all of this info into another file. I opened it
    file = fopen (image2.bmp, "wb");

    butI don t know how to use fwrite in otder to wite all the information stored in my structure. Can someone please help me?

  2. #2
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    Long Beach, CA
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    If you can use fread, you can use fwrite. They're virtually identical, except that one reads and the other writes. Same basic parameters, same order: pointer to data, item size, number of items, file.

    However, you're using fread wrong. It takes 4 parameters, and you're only providing 3. See the documentation.

    Your compiler should have warned you about that. You need to make sure you're #include'ing the proper headers in your program and have turned on your compiler warnings. In fact, set them to the strictest warnings possible, especially as you're learning to program. It will help you find errors.

    You also should be very careful about using fread and fwrite to write entire structs, as you can run into issues with struct member alignment and padding. Check these two links for more info. You probably want to read the header field-by-field into the individual struct members.

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