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STDIO(3) Library Functions Manual STDIO(3) NAME stdio - standard input/output library functions LIBRARY Standard C Library (libc, -lc) SYNOPSIS #include <stdio.h> FILE *stdin; FILE *stdout; FILE *stderr; DESCRIPTION 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. 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. Creating 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, the position indicator will be placed the end-of-file. The position indicator is maintained by subsequent 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 read 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 repositioned 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. This implementation needs and makes no distinction between "text" and "binary" streams. In effect, all streams are binary. No translation is performed and no extra padding appears on any stream. At program startup, three streams are predefined and need not be opened explicitly: 1. standard input for reading conventional input, 2. standard output for writing conventional output, and 3. standard error for writing diagnostic output. These streams are abbreviated stdin, stdout, and stderr. Initially, the standard error stream is unbuffered; the standard input and output streams are fully buffered if and only if the streams do not refer to an interactive or "terminal" device, as determined by the isatty(3) function. In fact, all freshly-opened streams that refer to terminal devices default to line buffering, and pending output to such streams is written automatically whenever an such an input stream is read. Note that this applies only to "true reads"; if the read request can be satisfied by existing buffered data, no automatic flush will occur. In these cases, or when a large amount of computation is done after printing part of a line on an output terminal, it is necessary to fflush(3) the standard output before going off and computing so that the output will appear. Alternatively, these defaults may be modified via the setvbuf(3) function. IMPLEMENTATION NOTES In multi-threaded applications, operations on streams perform implicit locking, except for the getc_unlocked(), getchar_unlocked(), putc_unlocked(), and putchar_unlocked() functions. Explicit control of stream locking is available through the flockfile(), ftrylockfile(), and funlockfile() functions . The following are defined as macros; these names may not be re-used 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, SEE_CUR, TMP_MAX, clearerr(), feof(), ferror(), fileno(), freopen(), fwopen(), getc(), getc_unlocked(), getchar(), getchar_unlocked(), putc(), putc_unlocked(), putchar(), putchar_unlocked(), stderr, stdin, stdout. Function versions of the macro functions feof(), ferror(), clearerr(), fileno(), getc(), getc_unlocked(), getchar(), getchar_unlocked(), putc(), putc_unlocked(), putchar(), and putchar_unlocked() exist and will be used if the macros definitions are explicitly removed. SEE ALSO close(2), open(2), read(2), write(2) STANDARDS The stdio library conforms to ANSI X3.159-1989 ("ANSI C89"). LIST OF FUNCTIONS Function Description asprintf formatted output conversion with allocation asprintf_l formatted output conversion with allocation clearerr check and reset stream status dprintf formatted output conversion dprintf_l formatted output conversion fclose close a stream fdopen stream open functions feof check and reset stream status ferror check and reset stream status fflush flush a stream fgetc get next character or word from input stream fgetln get a line from a stream fgetpos reposition a stream fgets get a line from a stream fgetwc get next wide character from input stream fileno check and reset stream status flockfile lock a stream fmemopen open a stream that points to a memory buffer fopen stream open functions fprintf formatted output conversion fprintf_l formatted output conversion fpurge flush a stream fputc output a character or word to a stream fputs output a line to a stream fputwc output a wide character to a stream fread binary stream input/output freopen stream open functions fropen open a stream fscanf input format conversion fscanf_l input format conversion fseek reposition a stream fseeko reposition a stream fsetpos reposition a stream ftell reposition a stream ftello reposition a stream ftrylockfile lock a stream (non-blocking) funlockfile unlock a stream funopen open a stream funopen2 open a stream, with flush support fwide set/get orientation of a stream fwopen open a stream fwrite binary stream input/output getc get next character or word from input stream getc_unlocked get next character or word from input stream (no implicit locking) getchar get next character or word from input stream getchar_unlocked get next character or word from input stream (no implicit locking) getdelim get a delimited record from a stream getline get a line from a stream gets get a line from a stream getw get next character or word from input stream getwc get next wide character from input stream getwchar get next wide character from input stream mkstemp create unique temporary file mktemp create unique temporary file open_memstream open memory as a stream popen open a program as a stream popenve open a program as a stream pclose close an opened program stream perror system error messages printf formatted output conversion printf_l formatted output conversion putc output a character or word to a stream putc_unlocked output a character or word to a stream (no implicit locking) putchar output a character or word to a stream putchar_unlocked output a character or word to a stream (no implicit locking) puts output a line to a stream putw output a character or word to a stream putwc output a wide character to a stream putwchar output a wide character to a stream remove remove directory entry rewind reposition a stream scanf input format conversion scanf_l input format conversion setbuf stream buffering operations setbuffer stream buffering operations setlinebuf stream buffering operations setvbuf stream buffering operations snprintf formatted output conversion snprintf_l formatted output conversion sprintf formatted output conversion sscanf input format conversion sscanf_l input format conversion strerror system error messages sys_errlist system error messages sys_nerr system error messages tempnam temporary file routines tmpfile temporary file routines tmpnam temporary file routines ungetc un-get character from input stream ungetwc un-get wide character from input stream vasprintf formatted output conversion with allocation vasprintf_l formatted output conversion with allocation vdprintf formatted output conversion vdprintf_l formatted output conversion vfprintf formatted output conversion vfprintf_l formatted output conversion vfscanf input format conversion vfscanf_l input format conversion vprintf formatted output conversion vprintf_l formatted output conversion vscanf input format conversion vscanf_l input format conversion vsnprintf formatted output conversion vsnprintf_l formatted output conversion vsprintf formatted output conversion vsprintf_l formatted output conversion vsscanf input format conversion vsscanf_l input format conversion BUGS The standard buffered functions do not interact well with certain other library and system functions, especially vfork(2) and abort(3). NetBSD 8.0 September 6, 2015 NetBSD 8.0