unlocked_stdio - Man Page

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).

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 safetyMT-Safe race:stream
getchar_unlocked(), getwchar_unlocked()Thread safetyMT-Unsafe race:stdin
putchar_unlocked(), putwchar_unlocked()Thread safetyMT-Unsafe race:stdout
feof_unlocked(), ferror_unlocked(), fileno_unlocked()Thread safetyMT-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.

See Also

flockfile(3), stdio(3)

Referenced By

ferror(3), fflush(3), fgetc(3), fgetwc(3), fgetws(3), fileno(3), flockfile(3), fputwc(3), fputws(3), fread(3), gets(3), getwchar(3), puts(3), putwchar(3), stdio(3).

The man pages clearerr_unlocked(3), feof_unlocked(3), ferror_unlocked(3), fflush_unlocked(3), fgetc_unlocked(3), fgets_unlocked(3), fgetwc_unlocked(3), fgetws_unlocked(3), fileno_unlocked(3), fputc_unlocked(3), fputs_unlocked(3), fputwc_unlocked(3), fputws_unlocked(3), fread_unlocked(3), fwrite_unlocked(3), getchar_unlocked(3), getc_unlocked(3), getwchar_unlocked(3), getwc_unlocked(3), putchar_unlocked(3), putc_unlocked(3), putwchar_unlocked(3) and putwc_unlocked(3) are aliases of unlocked_stdio(3).

2023-02-05 Linux man-pages 6.03