Padding a Bitmap pixel array

Question

I\'m making a program that creates a bitmap file in C. it\'s using 24-bit colour.

I\'m writing the file in 3 stages, i first write the FileHeader, then the InfoHeade

Answer 1

You are not padding rows to word size, you are padding the current file position. And it doesn't work because the size of your headers add up to 54 -- not a multiple of 4.

Instead of using ftell to retrieve the 'current position', use maths. Make your pad an unsigned long, and insert before your loops:

int npad = (sizeof(IMAGE)*width) & 3;
if (npad)
  npad = 4-npad;

Then, instead of the while(ftell .. loop, write out the number of required bytes immediately:

fwrite (&pad, 1,npad, n_img);

npad will range from 0..3, that's why you have to make pad a 4-byte integer.