1 .\" Copyright (c) 1990, 1991 The Regents of the University of California.
2 .\" All rights reserved.
4 .\" This code is derived from software contributed to Berkeley by
5 .\" Chris Torek and the American National Standards Committee X3,
6 .\" on Information Processing Systems.
8 .\" Redistribution and use in source and binary forms, with or without
9 .\" modification, are permitted provided that the following conditions
11 .\" 1. Redistributions of source code must retain the above copyright
12 .\" notice, this list of conditions and the following disclaimer.
13 .\" 2. Redistributions in binary form must reproduce the above copyright
14 .\" notice, this list of conditions and the following disclaimer in the
15 .\" documentation and/or other materials provided with the distribution.
16 .\" 3. All advertising materials mentioning features or use of this software
17 .\" must display the following acknowledgement:
18 .\" This product includes software developed by the University of
19 .\" California, Berkeley and its contributors.
20 .\" 4. Neither the name of the University nor the names of its contributors
21 .\" may be used to endorse or promote products derived from this software
22 .\" without specific prior written permission.
24 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
25 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
26 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
27 .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
28 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
29 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
30 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
31 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
32 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
33 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
36 .\" @(#)scanf.3 6.14 (Berkeley) 1/8/93
38 .\" Converted for Linux, Mon Nov 29 15:22:01 1993, faith@cs.unc.edu
39 .\" modified to resemble the GNU libio setup used in the Linux libc
40 .\" used in versions 4.x (x>4) and 5 Helmut.Geyer@iwr.uni-heidelberg.de
41 .\" Modified, aeb, 970121
42 .\" 2005-07-14, mtk, added description of %n$ form; various text
43 .\" incorporated from the GNU C library documentation ((C) The
44 .\" Free Software Foundation); other parts substantially rewritten.
47 .\" Add ERRORS section.
48 .\" Document the 'a' and 'm' modifiers for dynamic string allocation.
50 .TH SCANF 3 2011-09-28 "GNU" "Linux Programmer's Manual"
52 scanf, fscanf, sscanf, vscanf, vsscanf, vfscanf \- input format conversion
57 .BI "int scanf(const char *" format ", ...);"
58 .BI "int fscanf(FILE *" stream ", const char *" format ", ...);"
59 .BI "int sscanf(const char *" str ", const char *" format ", ...);"
61 .B #include <stdarg.h>
63 .BI "int vscanf(const char *" format ", va_list " ap );
64 .BI "int vsscanf(const char *" str ", const char *" format ", va_list " ap );
65 .BI "int vfscanf(FILE *" stream ", const char *" format ", va_list " ap );
69 Feature Test Macro Requirements for glibc (see
70 .BR feature_test_macros (7)):
78 _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE ||
79 _POSIX_C_SOURCE\ >=\ 200112L;
88 family of functions scans input according to
91 This format may contain
92 .IR "conversion specifications" ;
93 the results from such conversions, if any,
94 are stored in the locations pointed to by the
100 argument must be of a type that is appropriate for the value returned
101 by the corresponding conversion specification.
103 If the number of conversion specifications in
105 exceeds the number of
107 arguments, the results are undefined.
110 arguments exceeds the number of conversion specifications, then the excess
112 arguments are evaluated, but are otherwise ignored.
116 function reads input from the standard input stream
119 reads input from the stream pointer
123 reads its input from the character string pointed to by
128 function is analogous to
130 and reads input from the stream pointer
132 using a variable argument list of pointers (see
136 function scans a variable argument list from the standard input and the
138 function scans it from a string; these are analogous to the
142 functions respectively.
146 string consists of a sequence of
148 which describe how to process the sequence of input characters.
149 If processing of a directive fails, no further input is read, and
152 A "failure" can be either of the following:
153 .IR "input failure" ,
154 meaning that input characters were unavailable, or
155 .IR "matching failure" ,
156 meaning that the input was inappropriate (see below).
158 A directive is one of the following:
161 A sequence of white-space characters (space, tab, newline, etc.; see
163 This directive matches any amount of white space,
164 including none, in the input.
167 An ordinary character (i.e., one other than white space or \(aq%\(aq).
168 This character must exactly match the next character of input.
171 A conversion specification,
172 which commences with a \(aq%\(aq (percent) character.
173 A sequence of characters from the input is converted according to
174 this specification, and the result is placed in the corresponding
177 If the next item of input does not match the conversion specification,
178 the conversion fails\(emthis is a
179 .IR "matching failure" .
182 .I conversion specification
185 begins with either the character \(aq%\(aq or the character sequence
186 "\fB%\fP\fIn\fP\fB$\fP"
187 (see below for the distinction) followed by:
190 An optional \(aq*\(aq assignment-suppression character:
192 reads input as directed by the conversion specification,
193 but discards the input.
196 argument is required, and this specification is not
197 included in the count of successful assignments returned by
201 An optional \(aqa\(aq character.
202 This is used with string conversions, and relieves the caller of the
203 need to allocate a corresponding buffer to hold the input: instead,
205 allocates a buffer of sufficient size,
206 and assigns the address of this buffer to the corresponding
208 argument, which should be a pointer to a
210 variable (this variable does not need to be initialized before the call).
211 The caller should subsequently
213 this buffer when it is no longer required.
214 This is a GNU extension;
215 C99 employs the \(aqa\(aq character as a conversion specifier (and
216 it can also be used as such in the GNU implementation).
219 An optional decimal integer which specifies the
220 .IR "maximum field width" .
221 Reading of characters stops either when this maximum is reached or
222 when a nonmatching character is found, whichever happens first.
223 Most conversions discard initial white space characters (the exceptions
225 and these discarded characters don't count toward the maximum field width.
226 String input conversions store a terminating null byte (\(aq\\0\(aq)
227 to mark the end of the input;
228 the maximum field width does not include this terminator.
232 .IR "type modifier character" .
235 type modifier is used with integer conversions such as
237 to specify that the corresponding
241 rather than a pointer to an
246 .I "conversion specifier"
247 that specifies the type of input conversion to be performed.
249 The conversion specifications in
251 are of two forms, either beginning with \(aq%\(aq or beginning with
252 "\fB%\fP\fIn\fP\fB$\fP".
253 The two forms should not be mixed in the same
255 string, except that a string containing
256 "\fB%\fP\fIn\fP\fB$\fP"
257 specifications can include
264 specifications then these correspond in order with successive
268 "\fB%\fP\fIn\fP\fB$\fP"
269 form (which is specified in POSIX.1-2001, but not C99),
271 is a decimal integer that specifies that the converted input should
272 be placed in the location referred to by the
279 .I "type modifier characters"
280 can appear in a conversion specification:
283 Indicates that the conversion will be one of
284 \fBd\fP, \fBi\fP, \fBo\fP, \fBu\fP, \fBx\fP, \fBX\fP, or \fBn\fP
285 and the next pointer is a pointer to a
288 .I unsigned short int
295 but the next pointer is a pointer to a
298 .IR "unsigned char" .
303 but the next pointer is a pointer to an
307 This modifier was introduced in C99.
310 Indicates either that the conversion will be one of
311 \fBd\fP, \fBi\fP, \fBo\fP, \fBu\fP, \fBx\fP, \fBX\fP, or \fBn\fP
312 and the next pointer is a pointer to a
318 or that the conversion will be one of
319 \fBe\fP, \fBf\fP, or \fBg\fP
320 and the next pointer is a pointer to
326 characters is equivalent to
332 the corresponding parameter is considered
333 as a pointer to a wide character or wide-character string respectively.
334 .\" This use of l was introduced in Amendment 1 to ISO C90.
337 Indicates that the conversion will be either
338 \fBe\fP, \fBf\fP, or \fBg\fP
339 and the next pointer is a pointer to
341 or the conversion will be
342 \fBd\fP, \fBi\fP, \fBo\fP, \fBu\fP, or \fBx\fP
343 and the next pointer is a pointer to
345 .\" MTK, Jul 05: The following is no longer true for modern
346 .\" ANSI C (i.e., C99):
347 .\" (Note that long long is not an
349 .\" type. Any program using this will not be portable to all
355 This specifier does not exist in ANSI C.
360 but the next pointer is a pointer to a
362 This modifier was introduced in C99.
367 but the next pointer is a pointer to a
369 This modifier was introduced in C99.
372 .I "conversion specifiers"
376 Matches a literal \(aq%\(aq.
379 in the format string matches a
380 single input \(aq%\(aq character.
381 No conversion is done (but initial white space characters are discarded),
382 and assignment does not occur.
385 Matches an optionally signed decimal integer;
386 the next pointer must be a pointer to
392 this exists only for backward compatibility.
393 (Note: thus only in libc4.
394 In libc5 and glibc the
396 is silently ignored, causing old programs to fail mysteriously.)
399 Matches an optionally signed integer; the next pointer must be a pointer to
401 The integer is read in base 16 if it begins with
405 in base 8 if it begins with
407 and in base 10 otherwise.
408 Only characters that correspond to the base are used.
411 Matches an unsigned octal integer; the next pointer must be a pointer to
415 Matches an unsigned decimal integer; the next pointer must be a
420 Matches an unsigned hexadecimal integer; the next pointer must
429 Matches an optionally signed floating-point number; the next pointer must
450 Matches a sequence of non-white-space characters;
451 the next pointer must be a pointer to character array that is
452 long enough to hold the input sequence and
453 the terminating null byte (\(aq\\0\(aq), which is added automatically.
454 The input string stops at white space or at the maximum field
455 width, whichever occurs first.
458 Matches a sequence of characters whose length is specified by the
459 .I maximum field width
460 (default 1); the next pointer must be a pointer to
462 and there must be enough room for all the characters (no terminating
465 The usual skip of leading white space is suppressed.
466 To skip white space first, use an explicit space in the format.
469 Matches a nonempty sequence of characters from the specified set of
470 accepted characters; the next pointer must be a pointer to
472 and there must be enough room for all the characters in the string, plus a
473 terminating null byte.
474 The usual skip of leading white space is suppressed.
475 The string is to be made up of characters in (or not in) a particular set;
476 the set is defined by the characters between the open bracket
478 character and a close bracket
483 those characters if the first character after the open bracket is a
486 To include a close bracket in the set, make it the first character after
487 the open bracket or the circumflex; any other position will end the set.
490 is also special; when placed between two other characters, it adds all
491 intervening characters to the set.
492 To include a hyphen, make it the last
493 character before the final close bracket.
497 the set "everything except close bracket, zero through nine, and hyphen".
498 The string ends with the appearance of a character not in the (or, with a
499 circumflex, in) set or when the field width runs out.
502 Matches a pointer value (as printed by
506 the next pointer must be a pointer to a pointer to
510 Nothing is expected; instead, the number of characters consumed thus far
511 from the input is stored through the next pointer, which must be a pointer
516 a conversion, although it can be suppressed with the
518 assignment-suppression character.
519 The C standard says: "Execution of a
521 directive does not increment
522 the assignment count returned at the completion of execution"
523 but the Corrigendum seems to contradict this.
525 not to make any assumptions on the effect of
527 conversions on the return value.
529 These functions return the number of input items
530 successfully matched and assigned,
531 which can be fewer than provided for,
532 or even zero in the event of an early matching failure.
536 is returned if the end of input is reached before either the first
537 successful conversion or a matching failure occurs.
539 is also returned if a read error occurs,
540 in which case the error indicator for the stream (see
544 is set indicate the error.
548 The file descriptor underlying
550 is marked nonblocking, and the read operation would block.
553 The file descriptor underlying
555 is invalid, or not open for reading.
558 Input byte sequence does not form a valid character.
561 The read operation was interrupted by a signal; see
565 Not enough arguments; or
573 The result of an integer conversion would exceed the size
574 that can be stored in the corresponding integer type.
581 conform to C89 and C99 and POSIX.1-2001.
582 These standards do not specify the
588 specifier is the 4.4BSD notation for
594 in integer conversions is the GNU notation.
596 The Linux version of these functions is based on the
605 for a more concise description.
607 The GNU C library supports a nonstandard extension that causes
608 the library to dynamically allocate a string of sufficient size
609 for input strings for the
612 \fB%a[\fP\fIrange\fP\fB]\fP
613 conversion specifiers.
614 .\" This feature seems to be present at least as far back as glibc 2.0.
615 To make use of this feature, specify
617 as a length modifier (thus
620 \fB%a[\fP\fIrange\fP\fB]\fP).
623 the returned string, as in the following example:
631 n = scanf("%a[a-z]", &p);
633 printf("read: %s\\n", p);
635 } else if (errno != 0) {
638 fprintf(stderr, "No matching characters\\n"):
643 As shown in the above example, it is only necessary to call
647 call successfully read a string.
651 modifier is not available if the program is compiled with
654 .IR "gcc -D_ISOC99_SOURCE"
657 is also specified), in which case the
659 is interpreted as a specifier for floating-point numbers (see above).
661 Since version 2.7, glibc also provides the
663 modifier for the same purpose as the
668 modifier has the following advantages:
670 It may also be applied to
672 conversion specifiers (e.g.,
675 It avoids ambiguity with respect to the
677 floating-point conversion specifier (and is unaffected by
681 It is specified in the upcoming revision of the POSIX.1 standard.
683 All functions are fully C89 conformant, but provide the
684 additional specifiers
688 as well as an additional behavior of the
693 The latter may be considered to be a bug, as it changes the
694 behavior of specifiers defined in C89.
696 Some combinations of the type modifiers and conversion
697 specifiers defined by ANSI C do not make sense
700 While they may have a well-defined behavior on Linux, this need not
701 to be so on other architectures.
702 Therefore it usually is better to use
703 modifiers that are not defined by ANSI C at all, that is, use
708 \fBd\fP, \fBi\fP, \fBo\fP, \fBu\fP, \fBx\fP, and \fBX\fP
714 is not the same as on 4.4BSD,
715 as it may be used in float conversions equivalently to