title: Best way to convert whole file to lowercase in C
body: <p>I was wondering if theres a realy good (performant) solution how to Convert a whole file to lower Case in C.
  I use fgetc convert the char to lower case and write it in another temp-file with fputc. At the end i remove the original and rename the tempfile to the old originals name. But i think there must be a better Solution for it. </p>