The printf/fprintf/sprintf family supports a width field in its format specifier. I have a doubt for the case of (non-wide) char arrays arguments:

Is the width field supposed to mean bytes or characters?

What is the (correct-de facto) behaviour if the char array corresponds to (say) a raw UTF-8 string? (I know that normally I should use some wide char type, that's not the point)

For example, in

char s[] = "ni\xc3\xb1o";  // utf8 encoded "niño"
fprintf(f,"%5s",s);

Is that function supposed to try to ouput just 5 bytes (plain C chars) (and you take responsability of misalignments or other problems if two bytes results in a textual characters) ?

Or is it supposed to try to compute the length of "textual characters" of the array? (decodifying it... according to the current locale?) (in the example, this would amount to find out that the string has 4 unicode chars, so it would add a space for padding).