STDIO(3) Linux Programmer's Manual STDIO(3)
stdio - standard input/output library functions
FILE *stdin; FILE *stdout; FILE *stderr;
The standard I/O library provides a simple and efficient buffered stream I/O interface. Input and output is mapped into logical data streams and the physical I/O characteristics are concealed. The func- tions and macros are listed below; more information is available from the individual man pages.
A stream is associated with an external file (which may be a physical device) by opening a file, which may involve creating a new file. Cre- ating an existing file causes its former contents to be discarded. If a file can support positioning requests (such as a disk file, as opposed to a terminal), then a file position indicator associated with the stream is positioned at the start of the file (byte zero), unless the file is opened with append mode. If append mode is used, it is unspecified whether the position indicator will be placed at the start or the end of the file. The position indicator is maintained by subse- quent reads, writes and positioning requests. All input occurs as if the characters were read by successive calls to the fgetc(3) function; all output takes place as if all characters were written by successive calls to the fputc(3) function.
A file is disassociated from a stream by closing the file. Output streams are flushed (any unwritten buffer contents are transferred to the host environment) before the stream is disassociated from the file. The value of a pointer to a FILE object is indeterminate after a file is closed (garbage).
A file may be subsequently reopened, by the same or another program execution, and its contents reclaimed or modified (if it can be reposi- tioned at the start). If the main function returns to its original caller, or the exit(3) function is called, all open files are closed (hence all output streams are flushed) before program termination. Other methods of program termination, such as abort(3) do not bother about closing files properly.
At program startup, three text streams are predefined and need not be opened explicitly: standard input (for reading conventional input), standard output (for writing conventional output), and standard error (for writing diagnostic output). These streams are abbreviated stdin, stdout, and stderr. When opened, the standard error stream is not fully buffered; the standard input and output streams are fully buffered if and only if the streams do not refer to an interactive device.
Output streams that refer to terminal devices are always line buffered by default; pending output to such streams is written automatically whenever an input stream that refers to a terminal device is read. In cases where a large amount of computation is done after printing part of a line on an output terminal, it is necessary to fflush(3) the stan- dard output before going off and computing so that the output will appear.
The stdio library is a part of the library libc and routines are auto- matically loaded as needed by cc(1). The SYNOPSIS sections of the fol- lowing manual pages indicate which include files are to be used, what the compiler declaration for the function looks like and which external variables are of interest.
The following are defined as macros; these names may not be reused without first removing their current definitions with #undef: BUFSIZ, EOF, FILENAME_MAX, FOPEN_MAX, L_cuserid, L_ctermid, L_tmpnam, NULL, SEEK_END, SEEK_SET, SEEK_CUR, TMP_MAX, clearerr, feof, ferror, fileno, getc, getchar, putc, putchar, stderr, stdin, stdout. Function versions of the macro functions feof, ferror, clearerr, fileno, getc, getchar, putc, and putchar exist and will be used if the macros definitions are explicitly removed.
List of functions Function Description ---------------------------------------------------------------------- clearerr(3) check and reset stream status fclose(3) close a stream fdopen(3) stream open functions feof(3) check and reset stream status ferror(3) check and reset stream status fflush(3) flush a stream fgetc(3) get next character or word from input stream fgetpos(3) reposition a stream fgets(3) get a line from a stream fileno(3) return the integer descriptor of the argument stream fopen(3) stream open functions fprintf(3) formatted output conversion fpurge(3) flush a stream fputc(3) output a character or word to a stream fputs(3) output a line to a stream fread(3) binary stream input/output freopen(3) stream open functions fscanf(3) input format conversion fseek(3) reposition a stream fsetpos(3) reposition a stream ftell(3) reposition a stream fwrite(3) binary stream input/output getc(3) get next character or word from input stream getchar(3) get next character or word from input stream gets(3) get a line from a stream getw(3) get next character or word from input stream mktemp(3) make temporary filename (unique) perror(3) system error messages printf(3) formatted output conversion putc(3) output a character or word to a stream putchar(3) output a character or word to a stream puts(3) output a line to a stream putw(3) output a character or word to a stream remove(3) remove directory entry rewind(3) reposition a stream scanf(3) input format conversion setbuf(3) stream buffering operations setbuffer(3) stream buffering operations setlinebuf(3) stream buffering operations setvbuf(3) stream buffering operations sprintf(3) formatted output conversion sscanf(3) input format conversion strerror(3) system error messages sys_errlist(3) system error messages sys_nerr(3) system error messages tempnam(3) temporary file routines tmpfile(3) temporary file routines
tmpnam(3) temporary file routines ungetc(3) un-get character from input stream vfprintf(3) formatted output conversion vfscanf(3) input format conversion vprintf(3) formatted output conversion vscanf(3) input format conversion vsprintf(3) formatted output conversion vsscanf(3) input format conversion
The stdio library conforms to C89.
close(2), open(2), read(2), write(2), stdout(3), unlocked_stdio(3)
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