xref: /netbsd-src/lib/libc/stdio/scanf.3 (revision 23c8222edbfb0f0932d88a8351d3a0cf817dfb9e)
1.\"	$NetBSD: scanf.3,v 1.19 2003/09/08 17:54:32 wiz Exp $
2.\"
3.\" Copyright (c) 1990, 1991, 1993
4.\"	The Regents of the University of California.  All rights reserved.
5.\"
6.\" This code is derived from software contributed to Berkeley by
7.\" Chris Torek and the American National Standards Committee X3,
8.\" on Information Processing Systems.
9.\"
10.\" Redistribution and use in source and binary forms, with or without
11.\" modification, are permitted provided that the following conditions
12.\" are met:
13.\" 1. Redistributions of source code must retain the above copyright
14.\"    notice, this list of conditions and the following disclaimer.
15.\" 2. Redistributions in binary form must reproduce the above copyright
16.\"    notice, this list of conditions and the following disclaimer in the
17.\"    documentation and/or other materials provided with the distribution.
18.\" 3. Neither the name of the University nor the names of its contributors
19.\"    may be used to endorse or promote products derived from this software
20.\"    without specific prior written permission.
21.\"
22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32.\" SUCH DAMAGE.
33.\"
34.\"     @(#)scanf.3	8.2 (Berkeley) 12/11/93
35.\"
36.Dd April 30, 2001
37.Dt SCANF 3
38.Os
39.Sh NAME
40.Nm scanf ,
41.Nm fscanf ,
42.Nm sscanf ,
43.Nm vscanf ,
44.Nm vsscanf ,
45.Nm vfscanf
46.Nd input format conversion
47.Sh LIBRARY
48.Lb libc
49.Sh SYNOPSIS
50.In stdio.h
51.Ft int
52.Fn scanf "const char * restrict format" ...
53.Ft int
54.Fn fscanf "FILE * restrict stream" "const char * restrict format" ...
55.Ft int
56.Fn sscanf "const char * restrict str" "const char * restrict format" ...
57.In stdarg.h
58.Ft int
59.Fn vscanf "const char * restrict format" "va_list ap"
60.Ft int
61.Fn vsscanf "const char * restrict str" "const char * restrict format" "va_list ap"
62.Ft int
63.Fn vfscanf "FILE * restrict stream" "const char * restrict format" "va_list ap"
64.Sh DESCRIPTION
65The
66.Fn scanf
67family of functions scans input according to a
68.Fa format
69as described below.
70This format may contain
71.Em conversion specifiers ;
72the results from such conversions, if any,
73are stored through the
74.Em pointer
75arguments.
76The
77.Fn scanf
78function
79reads input from the standard input stream
80.Em stdin ,
81.Fn fscanf
82reads input from the stream pointer
83.Fa stream ,
84and
85.Fn sscanf
86reads its input from the character string pointed to by
87.Fa str .
88The
89.Fn vfscanf
90function
91is analogous to
92.Xr vfprintf 3
93and reads input from the stream pointer
94.Fa stream
95using a variable argument list of pointers (see
96.Xr stdarg 3 ) .
97The
98.Fn vscanf
99function scans a variable argument list from the standard input and
100the
101.Fn vsscanf
102function scans it from a string;
103these are analogous to
104the
105.Fn vprintf
106and
107.Fn vsprintf
108functions respectively.
109Each successive
110.Em pointer
111argument must correspond properly with
112each successive conversion specifier
113(but see `suppression' below).
114All conversions are introduced by the
115.Cm %
116(percent sign) character.
117The
118.Fa format
119string
120may also contain other characters.
121White space (such as blanks, tabs, or newlines) in the
122.Fa format
123string match any amount of white space, including none, in the input.
124Everything else
125matches only itself.
126Scanning stops
127when an input character does not match such a format character.
128Scanning also stops
129when an input conversion cannot be made (see below).
130.Sh CONVERSIONS
131Following the
132.Cm %
133character introducing a conversion
134there may be a number of
135.Em flag
136characters, as follows:
137.Bl -tag -width indent
138.It Cm *
139Suppresses assignment.
140The conversion that follows occurs as usual, but no pointer is used;
141the result of the conversion is simply discarded.
142.It Cm h
143Indicates that the conversion will be one of
144.Cm dioux
145or
146.Cm n
147and the next pointer is a pointer to a
148.Em short  int
149(rather than
150.Em int ) .
151.It Cm j
152Indicates that the conversion will be one of
153.Cm dioux
154or
155.Cm n
156and the next pointer is a pointer to an
157.Em intmax_t
158(rather than
159.Em int ) .
160.It Cm l
161Indicates either that the conversion will be one of
162.Cm dioux
163or
164.Cm n
165and the next pointer is a pointer to a
166.Em long  int
167(rather than
168.Em int ) ,
169or that the conversion will be one of
170.Cm efg
171and the next pointer is a pointer to
172.Em double
173(rather than
174.Em float ) .
175.It Cm q
176Indicates that the conversion will be one of
177.Cm dioux
178or
179.Cm n
180and the next pointer is a pointer to a
181.Em quad_t
182(rather than
183.Em int ) .
184.It Cm t
185Indicates that the conversion will be one of
186.Cm dioux
187or
188.Cm n
189and the next pointer is a pointer to a
190.Em ptrdiff_t
191(rather than
192.Em int ) .
193.It Cm z
194Indicates that the conversion will be one of
195.Cm dioux
196or
197.Cm n
198and the next pointer is a pointer to a
199.Em size_t
200(rather than
201.Em int ) .
202.It Cm L
203Indicates that the conversion will be
204.Cm efg
205and the next pointer is a pointer to
206.Em long double .
207.El
208.Pp
209In addition to these flags,
210there may be an optional maximum field width,
211expressed as a decimal integer,
212between the
213.Cm %
214and the conversion.
215If no width is given,
216a default of `infinity' is used (with one exception, below);
217otherwise at most this many characters are scanned
218in processing the conversion.
219Before conversion begins,
220most conversions skip white space;
221this white space is not counted against the field width.
222.Pp
223The following conversions are available:
224.Bl -tag -width XXXX
225.It Cm %
226Matches a literal `%'.
227That is, `%\&%' in the format string
228matches a single input `%' character.
229No conversion is done, and assignment does not occur.
230.It Cm d
231Matches an optionally signed decimal integer;
232the next pointer must be a pointer to
233.Em int .
234.It Cm D
235Equivalent to
236.Cm ld ;
237this exists only for backwards compatibility.
238.It Cm i
239Matches an optionally signed integer;
240the next pointer must be a pointer to
241.Em int .
242The integer is read in base 16 if it begins
243with
244.Ql 0x
245or
246.Ql 0X ,
247in base 8 if it begins with
248.Ql 0 ,
249and in base 10 otherwise.
250Only characters that correspond to the base are used.
251.It Cm o
252Matches an octal integer;
253the next pointer must be a pointer to
254.Em unsigned int .
255.It Cm O
256Equivalent to
257.Cm lo ;
258this exists for backwards compatibility.
259.It Cm u
260Matches an optionally signed decimal integer;
261the next pointer must be a pointer to
262.Em unsigned int .
263.It Cm x
264Matches an optionally signed hexadecimal integer;
265the next pointer must be a pointer to
266.Em unsigned int .
267.It Cm X
268Equivalent to
269.Cm x .
270.It Cm f
271Matches an optionally signed floating-point number;
272the next pointer must be a pointer to
273.Em float .
274.It Cm e
275Equivalent to
276.Cm f .
277.It Cm g
278Equivalent to
279.Cm f .
280.It Cm E
281Equivalent to
282.Cm f .
283.It Cm G
284Equivalent to
285.Cm f .
286.It Cm s
287Matches a sequence of non-white-space characters;
288the next pointer must be a pointer to
289.Em char ,
290and the array must be large enough to accept all the sequence and the
291terminating
292.Dv NUL
293character.
294The input string stops at white space
295or at the maximum field width, whichever occurs first.
296.It Cm c
297Matches a sequence of
298.Em width
299count
300characters (default 1);
301the next pointer must be a pointer to
302.Em char ,
303and there must be enough room for all the characters
304(no terminating
305.Dv NUL
306is added).
307The usual skip of leading white space is suppressed.
308To skip white space first, use an explicit space in the format.
309.It Cm \&[
310Matches a nonempty sequence of characters from the specified set
311of accepted characters;
312the next pointer must be a pointer to
313.Em char ,
314and there must be enough room for all the characters in the string,
315plus a terminating
316.Dv NUL
317character.
318The usual skip of leading white space is suppressed.
319The string is to be made up of characters in
320(or not in)
321a particular set;
322the set is defined by the characters between the open bracket
323.Cm [
324character
325and a close bracket
326.Cm ]
327character.
328The set
329.Em excludes
330those characters
331if the first character after the open bracket is a circumflex
332.Cm ^ .
333To include a close bracket in the set,
334make it the first character after the open bracket
335or the circumflex;
336any other position will end the set.
337The hyphen character
338.Cm -
339is also special;
340when placed between two other characters,
341it adds all intervening characters to the set.
342To include a hyphen,
343make it the last character before the final close bracket.
344For instance,
345.Ql [^]0-9-]
346means the set `everything except close bracket, zero through nine,
347and hyphen'.
348The string ends with the appearance of a character not in the
349(or, with a circumflex, in) set
350or when the field width runs out.
351.It Cm p
352Matches a pointer value (as printed by
353.Ql %p
354in
355.Xr printf 3 ) ;
356the next pointer must be a pointer to
357.Em void .
358.It Cm n
359Nothing is expected;
360instead, the number of characters consumed thus far from the input
361is stored through the next pointer,
362which must be a pointer to
363.Em int .
364This is
365.Em not
366a conversion, although it can be suppressed with the
367.Cm *
368flag.
369.El
370.Pp
371For backwards compatibility,
372other conversion characters (except
373.Ql \e0 )
374are taken as if they were
375.Ql %d
376or, if uppercase,
377.Ql %ld ,
378and a `conversion' of
379.Ql %\e0
380causes an immediate return of
381.Dv EOF .
382.Sh RETURN VALUES
383These
384functions
385return
386the number of input items assigned, which can be fewer than provided
387for, or even zero, in the event of a matching failure.
388Zero
389indicates that, while there was input available,
390no conversions were assigned;
391typically this is due to an invalid input character,
392such as an alphabetic character for a
393.Ql %d
394conversion.
395The value
396.Dv EOF
397is returned if an input failure occurs before any conversion such as an
398end-of-file occurs.
399If an error or end-of-file occurs after conversion has begun,
400the number of conversions which were successfully completed is returned.
401.Sh SEE ALSO
402.Xr getc 3 ,
403.Xr printf 3 ,
404.Xr strtod 3 ,
405.Xr strtol 3 ,
406.Xr strtoul 3
407.Sh STANDARDS
408The functions
409.Fn fscanf ,
410.Fn scanf ,
411and
412.Fn sscanf
413conform to
414.St -isoC-90 .
415The
416.Cm %j ,
417.Cm %t
418and
419.Cm %z
420conversion format modifiers
421conform to
422.St -isoC-99 .
423The
424.Fn vfscanf ,
425.Fn vscanf
426and
427.Fn vsscanf
428functions conform to
429.St -isoC-99 .
430.Sh HISTORY
431The functions
432.Fn vscanf ,
433.Fn vsscanf
434and
435.Fn vfscanf
436appeared in
437.Bx 4.4
438or even
439.Bx 4.3 .
440.Sh NOTES
441All of the backwards compatibility formats will be removed in the future.
442.Sh BUGS
443Numerical strings are truncated to 512 characters; for example,
444.Cm %f
445and
446.Cm %d
447are implicitly
448.Cm %512f
449and
450.Cm %512d .
451