xref: /freebsd/lib/libc/stdio/scanf.3 (revision a220d00e74dd245b4fca59c5eca0c53963686325)
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36.\"     @(#)scanf.3	8.2 (Berkeley) 12/11/93
37.\" $FreeBSD$
38.\"
39.Dd December 11, 1993
40.Dt SCANF 3
41.Os
42.Sh NAME
43.Nm scanf ,
44.Nm fscanf ,
45.Nm sscanf ,
46.Nm vscanf ,
47.Nm vsscanf ,
48.Nm vfscanf
49.Nd input format conversion
50.Sh LIBRARY
51.Lb libc
52.Sh SYNOPSIS
53.In stdio.h
54.Ft int
55.Fn scanf "const char *format" ...
56.Ft int
57.Fn fscanf "FILE *stream" "const char *format" ...
58.Ft int
59.Fn sscanf "const char *str" "const char *format" ...
60.In stdarg.h
61.Ft int
62.Fn vscanf "const char *format" "va_list ap"
63.Ft int
64.Fn vsscanf "const char *str" "const char *format" "va_list ap"
65.Ft int
66.Fn vfscanf "FILE *stream" "const char *format" "va_list ap"
67.Sh DESCRIPTION
68The
69.Fn scanf
70family of functions scans input according to a
71.Fa format
72as described below.
73This format may contain
74.Em conversion specifiers ;
75the results from such conversions, if any,
76are stored through the
77.Em pointer
78arguments.
79The
80.Fn scanf
81function
82reads input from the standard input stream
83.Em stdin ,
84.Fn fscanf
85reads input from the stream pointer
86.Fa stream ,
87and
88.Fn sscanf
89reads its input from the character string pointed to by
90.Fa str .
91The
92.Fn vfscanf
93function
94is analogous to
95.Xr vfprintf 3
96and reads input from the stream pointer
97.Fa stream
98using a variable argument list of pointers (see
99.Xr stdarg 3 ) .
100The
101.Fn vscanf
102function scans a variable argument list from the standard input and
103the
104.Fn vsscanf
105function scans it from a string;
106these are analogous to
107the
108.Fn vprintf
109and
110.Fn vsprintf
111functions respectively.
112Each successive
113.Em pointer
114argument must correspond properly with
115each successive conversion specifier
116(but see `suppression' below).
117All conversions are introduced by the
118.Cm %
119(percent sign) character.
120The
121.Fa format
122string
123may also contain other characters.
124White space (such as blanks, tabs, or newlines) in the
125.Fa format
126string match any amount of white space, including none, in the input.
127Everything else
128matches only itself.
129Scanning stops
130when an input character does not match such a format character.
131Scanning also stops
132when an input conversion cannot be made (see below).
133.Sh CONVERSIONS
134Following the
135.Cm %
136character introducing a conversion
137there may be a number of
138.Em flag
139characters, as follows:
140.Bl -tag -width indent
141.It Cm *
142Suppresses assignment.
143The conversion that follows occurs as usual, but no pointer is used;
144the result of the conversion is simply discarded.
145.It Cm h
146Indicates that the conversion will be one of
147.Cm dioux
148or
149.Cm n
150and the next pointer is a pointer to a
151.Em short  int
152(rather than
153.Em int ) .
154.It Cm l
155Indicates either that the conversion will be one of
156.Cm dioux
157or
158.Cm n
159and the next pointer is a pointer to a
160.Em long  int
161(rather than
162.Em int ) ,
163or that the conversion will be one of
164.Cm efg
165and the next pointer is a pointer to
166.Em double
167(rather than
168.Em float ) .
169.It Cm L
170Indicates that the conversion will be
171.Cm efg
172and the next pointer is a pointer to
173.Em long double .
174(This type is not implemented; the
175.Cm L
176flag is currently ignored.)
177.It Cm q
178Indicates either that the conversion will be one of
179.Cm dioux
180or
181.Cm n
182and the next pointer is a pointer to a
183.Em long long int
184(rather than
185.Em int ) ,
186.El
187.Pp
188In addition to these flags,
189there may be an optional maximum field width,
190expressed as a decimal integer,
191between the
192.Cm %
193and the conversion.
194If no width is given,
195a default of `infinity' is used (with one exception, below);
196otherwise at most this many characters are scanned
197in processing the conversion.
198Before conversion begins,
199most conversions skip white space;
200this white space is not counted against the field width.
201.Pp
202The following conversions are available:
203.Bl -tag -width XXXX
204.It Cm %
205Matches a literal `%'.
206That is, `%\&%' in the format string
207matches a single input `%' character.
208No conversion is done, and assignment does not occur.
209.It Cm d
210Matches an optionally signed decimal integer;
211the next pointer must be a pointer to
212.Em int .
213.It Cm D
214Equivalent to
215.Cm ld ;
216this exists only for backwards compatibility.
217.It Cm i
218Matches an optionally signed integer;
219the next pointer must be a pointer to
220.Em int .
221The integer is read in base 16 if it begins
222with
223.Ql 0x
224or
225.Ql 0X ,
226in base 8 if it begins with
227.Ql 0 ,
228and in base 10 otherwise.
229Only characters that correspond to the base are used.
230.It Cm o
231Matches an octal integer;
232the next pointer must be a pointer to
233.Em unsigned int .
234.It Cm O
235Equivalent to
236.Cm lo ;
237this exists for backwards compatibility.
238.It Cm u
239Matches an optionally signed decimal integer;
240the next pointer must be a pointer to
241.Em unsigned int .
242.It Cm x
243Matches an optionally signed hexadecimal integer;
244the next pointer must be a pointer to
245.Em unsigned int .
246.It Cm X
247Equivalent to
248.Cm lx ;
249this violates the
250.St -isoC ,
251but is backwards compatible with previous
252.Ux
253systems.
254.It Cm f
255Matches an optionally signed floating-point number;
256the next pointer must be a pointer to
257.Em float .
258.It Cm e
259Equivalent to
260.Cm f .
261.It Cm g
262Equivalent to
263.Cm f .
264.It Cm E
265Equivalent to
266.Cm lf ;
267this violates the
268.St -isoC ,
269but is backwards compatible with previous
270.Ux
271systems.
272.It Cm F
273Equivalent to
274.Cm lf ;
275this exists only for backwards compatibility.
276.It Cm s
277Matches a sequence of non-white-space characters;
278the next pointer must be a pointer to
279.Em char ,
280and the array must be large enough to accept all the sequence and the
281terminating
282.Dv NUL
283character.
284The input string stops at white space
285or at the maximum field width, whichever occurs first.
286.It Cm c
287Matches a sequence of
288.Em width
289count
290characters (default 1);
291the next pointer must be a pointer to
292.Em char ,
293and there must be enough room for all the characters
294(no terminating
295.Dv NUL
296is added).
297The usual skip of leading white space is suppressed.
298To skip white space first, use an explicit space in the format.
299.It Cm \&[
300Matches a nonempty sequence of characters from the specified set
301of accepted characters;
302the next pointer must be a pointer to
303.Em char ,
304and there must be enough room for all the characters in the string,
305plus a terminating
306.Dv NUL
307character.
308The usual skip of leading white space is suppressed.
309The string is to be made up of characters in
310(or not in)
311a particular set;
312the set is defined by the characters between the open bracket
313.Cm [
314character
315and a close bracket
316.Cm ]
317character.
318The set
319.Em excludes
320those characters
321if the first character after the open bracket is a circumflex
322.Cm ^ .
323To include a close bracket in the set,
324make it the first character after the open bracket
325or the circumflex;
326any other position will end the set.
327The hyphen character
328.Cm -
329is also special;
330when placed between two other characters,
331it adds all intervening characters to the set.
332To include a hyphen,
333make it the last character before the final close bracket.
334For instance,
335.Ql [^]0-9-]
336means the set `everything except close bracket, zero through nine,
337and hyphen'.
338The string ends with the appearance of a character not in the
339(or, with a circumflex, in) set
340or when the field width runs out.
341.It Cm p
342Matches a pointer value (as printed by
343.Ql %p
344in
345.Xr printf 3 ) ;
346the next pointer must be a pointer to
347.Em void .
348.It Cm n
349Nothing is expected;
350instead, the number of characters consumed thus far from the input
351is stored through the next pointer,
352which must be a pointer to
353.Em int .
354This is
355.Em not
356a conversion, although it can be suppressed with the
357.Cm *
358flag.
359.El
360.Pp
361The decimal point
362character is defined in the program's locale (category
363.Dv LC_NUMERIC ) .
364.Pp
365For backwards compatibility,
366other conversion characters (except
367.Ql \e0 )
368are taken as if they were
369.Ql %d
370or, if uppercase,
371.Ql %ld ,
372and a `conversion' of
373.Ql %\e0
374causes an immediate return of
375.Dv EOF .
376The
377.Cm F
378and
379.Cm X
380conversions will be changed in the future
381to conform to the
382.Tn ANSI
383C standard,
384after which they will act like
385.Cm f
386and
387.Cm x
388respectively.
389.Sh RETURN VALUES
390These
391functions
392return
393the number of input items assigned, which can be fewer than provided
394for, or even zero, in the event of a matching failure.
395Zero
396indicates that, while there was input available,
397no conversions were assigned;
398typically this is due to an invalid input character,
399such as an alphabetic character for a
400.Ql %d
401conversion.
402The value
403.Dv EOF
404is returned if an input failure occurs before any conversion such as an
405end-of-file occurs.
406If an error or end-of-file occurs after conversion
407has begun,
408the number of conversions which were successfully completed is returned.
409.Sh SEE ALSO
410.Xr getc 3 ,
411.Xr printf 3 ,
412.Xr strtod 3 ,
413.Xr strtol 3 ,
414.Xr strtoul 3
415.Sh STANDARDS
416The functions
417.Fn fscanf ,
418.Fn scanf ,
419and
420.Fn sscanf
421conform to
422.St -isoC .
423.Sh HISTORY
424The functions
425.Fn vscanf ,
426.Fn vsscanf
427and
428.Fn vfscanf
429are new to this release.
430.Sh BUGS
431The current situation with
432.Cm %F
433and
434.Cm %X
435conversions is unfortunate.
436.Pp
437All of the backwards compatibility formats will be removed in the future.
438.Pp
439Numerical strings are truncated to 512 characters; for example,
440.Cm %f
441and
442.Cm %d
443are implicitly
444.Cm %512f
445and
446.Cm %512d .
447