Scroll to navigation

unlocked_stdio(3) Library Functions Manual unlocked_stdio(3)


getc_unlocked, getchar_unlocked, putc_unlocked, putchar_unlocked - nonlocking stdio functions


Standard C library (libc, -lc)


#include <stdio.h>
int getc_unlocked(FILE *stream);
int getchar_unlocked(void);
int putc_unlocked(int c, FILE *stream);
int putchar_unlocked(int c);
void clearerr_unlocked(FILE *stream);
int feof_unlocked(FILE *stream);
int ferror_unlocked(FILE *stream);
int fileno_unlocked(FILE *stream);
int fflush_unlocked(FILE *stream);
int fgetc_unlocked(FILE *stream);
int fputc_unlocked(int c, FILE *stream);
size_t fread_unlocked(void ptr[restrict .size * .n],
                      size_t size, size_t n,
                      FILE *restrict stream);
size_t fwrite_unlocked(const void ptr[restrict .size * .n],
                      size_t size, size_t n,
                      FILE *restrict stream);
char *fgets_unlocked(char s[restrict .n], int n, FILE *restrict stream);
int fputs_unlocked(const char *restrict s, FILE *restrict stream);
#include <wchar.h>
wint_t getwc_unlocked(FILE *stream);
wint_t getwchar_unlocked(void);
wint_t fgetwc_unlocked(FILE *stream);
wint_t fputwc_unlocked(wchar_t wc, FILE *stream);
wint_t putwc_unlocked(wchar_t wc, FILE *stream);
wint_t putwchar_unlocked(wchar_t wc);
wchar_t *fgetws_unlocked(wchar_t ws[restrict .n], int n,
                      FILE *restrict stream);
int fputws_unlocked(const wchar_t *restrict ws,
                      FILE *restrict stream);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

getc_unlocked(), getchar_unlocked(), putc_unlocked(), putchar_unlocked():

/* glibc >= 2.24: */ _POSIX_C_SOURCE >= 199309L
|| /* glibc <= 2.23: */ _POSIX_C_SOURCE
|| /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE

clearerr_unlocked(), feof_unlocked(), ferror_unlocked(), fileno_unlocked(), fflush_unlocked(), fgetc_unlocked(), fputc_unlocked(), fread_unlocked(), fwrite_unlocked():

/* glibc >= 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE

fgets_unlocked(), fputs_unlocked(), getwc_unlocked(), getwchar_unlocked(), fgetwc_unlocked(), fputwc_unlocked(), putwchar_unlocked(), fgetws_unlocked(), fputws_unlocked():



Each of these functions has the same behavior as its counterpart without the "_unlocked" suffix, except that they do not use locking (they do not set locks themselves, and do not test for the presence of locks set by others) and hence are thread-unsafe. See flockfile(3).


For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
getc_unlocked (), putc_unlocked (), clearerr_unlocked (), fflush_unlocked (), fgetc_unlocked (), fputc_unlocked (), fread_unlocked (), fwrite_unlocked (), fgets_unlocked (), fputs_unlocked (), getwc_unlocked (), fgetwc_unlocked (), fputwc_unlocked (), putwc_unlocked (), fgetws_unlocked (), fputws_unlocked () Thread safety MT-Safe race:stream
getchar_unlocked (), getwchar_unlocked () Thread safety MT-Unsafe race:stdin
putchar_unlocked (), putwchar_unlocked () Thread safety MT-Unsafe race:stdout
feof_unlocked (), ferror_unlocked (), fileno_unlocked () Thread safety MT-Safe


The four functions getc_unlocked(), getchar_unlocked(), putc_unlocked(), putchar_unlocked() are in POSIX.1-2001 and POSIX.1-2008.

The nonstandard *_unlocked() variants occur on a few UNIX systems, and are available in recent glibc. They should probably not be used.


flockfile(3), stdio(3)

2023-02-05 Linux man-pages 6.03