Thanks for your reply! > Can you post an error message? The error messages are the ones which I produce: e.g. fp = fopen("Veränderung.txt","r"); if (!fp) { cout << "couldn't read file " << filename << endl; return 1; } In the above case, I would get the error message: couldn't read file Veränderung.txt It works fine with all filenames without Umlauts > Does the problem affect file names or > file data? I haven't checked the content of files so far, but it affects the filenames > What kind of files are you trying to access? ASCII