C structs & fread

I have a struct i want to read in from file. To be specific its a windows bmp. It works when i read in the values individually, but when I try and read the structure as a whole it gets the wrong values:


struct BITMAPFILEHEADER{
    unsigned short bfType;        // size: 2
    unsigned int bfSize;        // size: 4
    unsigned short bfReserved1;    // size: 2 
    unsigned short bfReserved2;    // size: 2 
    unsigned int bfOffBits;    //size: 4
};

// works
fread (&fileheader.bfType,2,1,imgFile);
fread (&fileheader.bfSize,4,1,imgFile);
fread (&fileheader.bfReserved1,2,1,imgFile);
fread (&fileheader.bfReserved2,2,1,imgFile);
fread (&fileheader.bfOffBits,4,1,imgFile);

// does not work right
fread (&fileheader,sizeof(BITMAPFILEHEADER),1,imgFile);

Learn Erlang binary syntax.

Your struct is not necessarily with size 2 and 4 entries.  For optimization purposes, depending on how the compiler feels like fucking with you, it could 4-byte align each field.  Dunno if it's the problem, but it's a possibility.  Faggot

http://docs.hp.com/en/8/pragmas.htm#pragma-pack

>>3
I looked at other code on the internet, and they use the same method

Is there a way to make sure the struct gets set the right way? COCKSUCKER

>>4
how would i use that?

>>1
either turn off forced alingment or expand your struct with 2 unused bytes, dumbass

>>6
got it, thanks alot >>4 =D

ONE WORD, THE FORCED ALIGNMENT OF DATA

Also don't forget your byte swapping.

fread (&fileheader.bfType,2,1,imgFile);
fread (&fileheader.bfSize,4,1,imgFile);
fread (&fileheader.bfReserved1,2,1,imgFile);
fread (&fileheader.bfReserved2,2,1,imgFile);
fread (&fileheader.bfOffBits,4,1,imgFile);

Learn to use the sizeof operator you stupid fuck instead of doing some elitist faggotry and directly writing the size.

1. Do not depend on specific sizes of int, shorts etc. Use stdint.h for that.
2. Do not read shit into a struct. The only guarantee about that is that you will get the same back if you wrote the struct with the exact same binary. Read shit into an array of u8_t's and extract the values from that.
3. Do not depend on the endianness of the computer. Use a macro to get shit by shifting the u8_t's (you can ifdef the macro to use type punning if appropriate).
4. Never believe something on the Internet without doublechecking.

>>11
Uh, no. Element sizes in a file are determined by the format, not the target runtime.

>>13
Uh, uh, uh.

Uh considered harmful

considered harmful considered harmful