fgetc / getc / getchar / ungetc - glibc

Split from the chapter glibc: stdio and Formatted I/O into the per-function layout; see the method page and the glibc ledger for coverage status.

Signature – int fgetc(FILE *stream); int getc(FILE *stream); int getchar(void); int ungetc(int c, FILE *stream); plus fgetc_unlocked, getc_unlocked, getchar_unlocked and the SVID word reader getw.

Semantics – read one byte as unsigned char, returned as int; EOF on end-of-file or error. The manual’s rule: store the result in an int, never a char, or EOF becomes indistinguishable from the valid byte (char)-1 (manual, Character Input). getc/getchar may be macros that evaluate the stream argument more than once – never pass a side-effecting expression. ungetc pushes one byte back: the next read returns it first. glibc supports pushing back several characters (read in reverse push order), pushing a byte that differs from the one read, and pushing without any prior read; ungetc(EOF, ...) is a no-op returning EOF; a successful pushback on a stream at EOF clears the EOF indicator; any positioning call discards pushed-back bytes (manual, Unreading). getw reads one int and cannot report -1 values – legacy, use fread.

Thread safety – locked variants MT-Safe; _unlocked variants need external flockfile.