3 - return matches, "errors" reference
4 - NULL ==> not in a meta state
10 - check all files are closed
12 - fopen returns an open file
13 - fclose must be passed an open file
14 - fgetc, fputc must be passed an open file
15 - EOF return from fgetc; read error when EOF set
16 - fputc error return EOF
19 - ferror - nonzero iff error indicator is set
20 - feof - nonzery iff eof is set
26 must call fseek between input and output, unless EOF!