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PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface
may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface
may not be implemented on Linux.
NAME
stdio.h — standard buffered input/output
SYNOPSIS
#include <stdio.h>
DESCRIPTION
Some of the functionality described on this reference page extends the ISO C standard. Applications shall
define the appropriate feature test macro (see the System Interfaces volume of POSIX.1‐2017, Section 2.2,
The Compilation Environment) to enable the visibility of these symbols in this header.
The <stdio.h> header shall define the following data types through typedef:
FILE A structure containing information about a file.
fpos_t A non-array type containing all information needed to specify uniquely every position
within a file.
off_t As described in <sys/types.h>.
size_t As described in <stddef.h>.
ssize_t As described in <sys/types.h>.
va_list As described in <stdarg.h>.
The <stdio.h> header shall define the following macros which shall expand to integer constant
expressions:
BUFSIZ Size of <stdio.h> buffers. This shall expand to a positive value.
L_ctermid Maximum size of character array to hold ctermid() output.
L_tmpnam Maximum size of character array to hold tmpnam() output.
The <stdio.h> header shall define the following macros which shall expand to integer constant expressions
with distinct values:
_IOFBF Input/output fully buffered.
_IOLBF Input/output line buffered.
_IONBF Input/output unbuffered.
The <stdio.h> header shall define the following macros which shall expand to integer constant expressions
with distinct values:
SEEK_CUR Seek relative to current position.
SEEK_END Seek relative to end-of-file.
SEEK_SET Seek relative to start-of-file.
The <stdio.h> header shall define the following macros which shall expand to integer constant expressions
denoting implementation limits:
{FILENAME_MAX}
Maximum size in bytes of the longest pathname that the implementation guarantees can be
opened.
{FOPEN_MAX} Number of streams which the implementation guarantees can be open simultaneously. The value
is at least eight.
{TMP_MAX} Minimum number of unique filenames generated by tmpnam(). Maximum number of times an
application can call tmpnam() reliably. The value of {TMP_MAX} is at least 25.
On XSI-conformant systems, the value of {TMP_MAX} is at least 10000.
The <stdio.h> header shall define the following macro which shall expand to an integer constant
expression with type int and a negative value:
EOF End-of-file return value.
The <stdio.h> header shall define NULL as described in <stddef.h>.
The <stdio.h> header shall define the following macro which shall expand to a string constant:
P_tmpdir Default directory prefix for tempnam().
The <stdio.h> header shall define the following macros which shall expand to expressions of type
``pointer to FILE'' that point to the FILE objects associated, respectively, with the standard error,
input, and output streams:
stderr Standard error output stream.
stdin Standard input stream.
stdout Standard output stream.
The following shall be declared as functions and may also be defined as macros. Function prototypes shall
be provided.
void clearerr(FILE *);
char *ctermid(char *);
int dprintf(int, const char *restrict, ...)
int fclose(FILE *);
FILE *fdopen(int, const char *);
int feof(FILE *);
int ferror(FILE *);
int fflush(FILE *);
int fgetc(FILE *);
int fgetpos(FILE *restrict, fpos_t *restrict);
char *fgets(char *restrict, int, FILE *restrict);
int fileno(FILE *);
void flockfile(FILE *);
FILE *fmemopen(void *restrict, size_t, const char *restrict);
FILE *fopen(const char *restrict, const char *restrict);
int fprintf(FILE *restrict, const char *restrict, ...);
int fputc(int, FILE *);
int fputs(const char *restrict, FILE *restrict);
size_t fread(void *restrict, size_t, size_t, FILE *restrict);
FILE *freopen(const char *restrict, const char *restrict,
FILE *restrict);
int fscanf(FILE *restrict, const char *restrict, ...);
int fseek(FILE *, long, int);
int fseeko(FILE *, off_t, int);
int fsetpos(FILE *, const fpos_t *);
long ftell(FILE *);
off_t ftello(FILE *);
int ftrylockfile(FILE *);
void funlockfile(FILE *);
size_t fwrite(const void *restrict, size_t, size_t, FILE *restrict);
int getc(FILE *);
int getchar(void);
int getc_unlocked(FILE *);
int getchar_unlocked(void);
ssize_t getdelim(char **restrict, size_t *restrict, int,
FILE *restrict);
ssize_t getline(char **restrict, size_t *restrict, FILE *restrict);
char *gets(char *);
FILE *open_memstream(char **, size_t *);
int pclose(FILE *);
void perror(const char *);
FILE *popen(const char *, const char *);
int printf(const char *restrict, ...);
int putc(int, FILE *);
int putchar(int);
int putc_unlocked(int, FILE *);
int putchar_unlocked(int);
int puts(const char *);
int remove(const char *);
int rename(const char *, const char *);
int renameat(int, const char *, int, const char *);
void rewind(FILE *);
int scanf(const char *restrict, ...);
void setbuf(FILE *restrict, char *restrict);
int setvbuf(FILE *restrict, char *restrict, int, size_t);
int snprintf(char *restrict, size_t, const char *restrict, ...);
int sprintf(char *restrict, const char *restrict, ...);
int sscanf(const char *restrict, const char *restrict, ...);
char *tempnam(const char *, const char *);
FILE *tmpfile(void);
char *tmpnam(char *);
int ungetc(int, FILE *);
int vdprintf(int, const char *restrict, va_list);
int vfprintf(FILE *restrict, const char *restrict, va_list);
int vfscanf(FILE *restrict, const char *restrict, va_list);
int vprintf(const char *restrict, va_list);
int vscanf(const char *restrict, va_list);
int vsnprintf(char *restrict, size_t, const char *restrict,
va_list);
int vsprintf(char *restrict, const char *restrict, va_list);
int vsscanf(const char *restrict, const char *restrict, va_list);
Inclusion of the <stdio.h> header may also make visible all symbols from <stddef.h>.
The following sections are informative.
APPLICATION USAGE
Since standard I/O streams may use an underlying file descriptor to access the file associated with a
stream, application developers need to be aware that {FOPEN_MAX} streams may not be available if file
descriptors are being used to access files that are not associated with streams.
RATIONALE
There is a conflict between the ISO C standard and the POSIX definition of the {TMP_MAX} macro that is
addressed by ISO/IEC 9899:1999 standard, Defect Report 336. The POSIX standard is in alignment with the
public record of the response to the Defect Report. This change has not yet been published as part of
the ISO C standard.
FUTURE DIRECTIONS
None.
SEE ALSO
<stdarg.h>, <stddef.h>, <sys_types.h>
The System Interfaces volume of POSIX.1‐2017, Section 2.2, The Compilation Environment, clearerr(),
ctermid(), fclose(), fdopen(), feof(), ferror(), fflush(), fgetc(), fgetpos(), fgets(), fileno(),
flockfile(), fmemopen(), fopen(), fprintf(), fputc(), fputs(), fread(), freopen(), fscanf(), fseek(),
fsetpos(), ftell(), fwrite(), getc(), getchar(), getc_unlocked(), getdelim(), getopt(), gets(),
open_memstream(), pclose(), perror(), popen(), putc(), putchar(), puts(), remove(), rename(), rewind(),
setbuf(), setvbuf(), stdin, system(), tempnam(), tmpfile(), tmpnam(), ungetc(), vfprintf(), vfscanf()
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original
IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document.
The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page are most likely to have been introduced
during the conversion of the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .