stdio.h — standard buffered input/output
#include <stdio.h>
[CX] Some of the functionality described on this reference page extends the ISO C standard. Applications shall define the appropriate feature test macro (see XSH 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 type containing information about a file. The FILE type may be an incomplete type.
- fpos_t
- A complete object type, other than an array type, capable of recording all the 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
- [CX] As described in <sys/types.h>.
- va_list
- [CX] 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. [CX] This shall expand to a positive value.
- L_ctermid
- [CX] Maximum size of character array to hold ctermid() output.
- L_tmpnam
- [OB] 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}
- [OB] 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.
[OB XSI] 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 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 *); [CX] char *ctermid(char *); int dprintf(int, const char *restrict, ...) int fclose(FILE *); [CX] 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); [CX] 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); [CX] int fseeko(FILE *, off_t, int); int fsetpos(FILE *, const fpos_t *); long ftell(FILE *); [CX] 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); [CX] 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); FILE *open_memstream(char **, size_t *); int pclose(FILE *); void perror(const char *); [CX] FILE *popen(const char *, const char *); int printf(const char *restrict, ...); int putc(int, FILE *); int putchar(int); [CX] int putc_unlocked(int, FILE *); int putchar_unlocked(int); int puts(const char *); int remove(const char *); int rename(const char *, const char *); [CX] 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, ...); FILE *tmpfile(void); [OB] char *tmpnam(char *); int ungetc(int, FILE *); [CX] 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);[CX] Inclusion of the <stdio.h> header may also make visible all symbols from <stddef.h>.
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.
Since the latest revision of the ISO C standard allows FILE to be an incomplete type (and POSIX also allows it), portable applications can no longer allocate or copy an object of type FILE; only pointers to objects of type FILE can be allocated.
None.
None.
<stdarg.h> , <stddef.h> , <sys/types.h>
XSH 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 , open_memstream , pclose , perror , popen , putc , putchar , puts , remove , rename , rewind , setbuf , setvbuf , stdin , system , tmpfile , tmpnam , ungetc , vfprintf , vfscanf
First released in Issue 1. Derived from Issue 1 of the SVID.
The DESCRIPTION is updated for alignment with the POSIX Threads Extension.
Large File System extensions are added.
The constant L_cuserid and the external variables optarg, opterr, optind, and optopt are marked as extensions and LEGACY.
The cuserid() and getopt() functions are marked LEGACY.
The constant L_cuserid and the external variables optarg, opterr, optind, and optopt are removed as they were previously marked LEGACY.
The cuserid(), getopt(), and getw() functions are removed as they were previously marked LEGACY.
Several functions are marked as part of the Thread-Safe Functions option.
This reference page is updated to align with the ISO/IEC 9899:1999 standard. Note that the description of the fpos_t type is now explicitly updated to exclude array types.
Extensions beyond the ISO C standard are marked.
Austin Group Interpretation 1003.1-2001 #172 is applied, adding rationale about a conflict for the definition of {TMP_MAX} with the ISO C standard.
SD5-XBD-ERN-99 is applied, adding APPLICATION USAGE.
The dprintf(), fmemopen(), getdelim(), getline(), open_memstream(), and vdprintf() functions are added from The Open Group Technical Standard, 2006, Extended API Set Part 1.
The renameat() function is added from The Open Group Technical Standard, 2006, Extended API Set Part 2.
The gets(), tmpnam(), and tempnam() functions and the L_tmpnam macro are marked obsolescent.
This reference page is clarified with respect to macros and symbolic constants, and a declaration for the off_t type is added.
POSIX.1-2008, Technical Corrigendum 1, XBD/TC1-2008/0065 [291,427] is applied.
Austin Group Defect 1054 is applied, allowing FILE to be an incomplete type.
Austin Group Defect 1302 is applied, aligning this header with the ISO/IEC 9899:2018 standard.
Austin Group Defect 1330 is applied, removing obsolescent interfaces.
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