Function for BMP color inverting doesn't work

Question

I wrote some quick code that is supposed to invert colors of a BMP image. I test with a 40x40 dimensional BMP image, created by paint. However the function seem to fill it e

Answer 1

The C11 draft specification has this to say about the problem

When a file is opened with update mode ('+' as the second or third character in the above list of mode argument values), both input and output may be performed on the associated stream. However, output shall not be directly followed by input without an intervening call to the fflush function or to a file positioning function (fseek, fsetpos, or rewind), and input shall not be directly followed by output without an intervening call to a file positioning function, unless the input operation encounters end- of-file.