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.
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18 .\" This product includes software developed by the University of
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20 .\" 4. Neither the name of the University nor the names of its contributors
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24 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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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.
46 .TH SCANF 3 2007-07-26 "GNU" "Linux Programmer's Manual"
48 scanf, fscanf, sscanf, vscanf, vsscanf, vfscanf \- input format conversion
53 .BI "int scanf(const char *" format ", ..." );
55 .BI "int fscanf(FILE *" stream ", const char *" format ", ..." );
57 .BI "int sscanf(const char *" str ", const char *" format ", ..." );
59 .B #include <stdarg.h>
60 .BI "int vscanf(const char *" format ", va_list " ap );
62 .BI "int vsscanf(const char *" str ", const char *" format ", va_list " ap );
64 .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)):
77 _XOPEN_SOURCE\ >=\ 600 || _ISOC99_SOURCE; or
82 family of functions scans input according to
85 This format may contain
86 .IR "conversion specifications" ;
87 the results from such conversions, if any,
88 are stored in the locations pointed to by the
94 argument must be of a type that is appropriate for the value returned
95 by the corresponding conversion specification.
97 If the number of conversion specifications in
101 arguments, the results are undefined.
104 arguments exceeds the number of conversion specifications, then the excess
106 arguments are evaluated, but are otherwise ignored.
110 function reads input from the standard input stream
113 reads input from the stream pointer
117 reads its input from the character string pointed to by
122 function is analogous to
124 and reads input from the stream pointer
126 using a variable argument list of pointers (see
130 function scans a variable argument list from the standard input and the
132 function scans it from a string; these are analogous to the
136 functions respectively.
140 string consists of a sequence of
142 which describe how to process the sequence of input characters.
143 If processing of a directive fails, no further input is read, and
146 A "failure" can be either of the following:
147 .IR "input failure" ,
148 meaning that input characters were unavailable, or
149 .IR "matching failure" ,
150 meaning that the input was inappropriate (see below).
152 A directive is one of the following:
155 A sequence of white-space characters (space, tab, newline, etc; see
157 This directive matches any amount of white space,
158 including none, in the input.
161 An ordinary character (i.e., one other than white space or '%').
162 This character must exactly match the next character of input.
165 A conversion specification, which commences with a '%' (percent) character.
166 A sequence of characters from the input is converted according to
167 this specification, and the result is placed in the corresponding
170 If the next item of input does not match the conversion specification,
171 the conversion fails \(em this is a
172 .IR "matching failure" .
175 .I conversion specification
178 begins with either the character '%' or the character sequence
179 "\fB%\fP\fIn\fP\fB$\fP"
180 (see below for the distinction) followed by:
183 An optional '*' assignment-suppression character:
185 reads input as directed by the conversion specification,
186 but discards the input.
189 argument is required, and this specification is not
190 included in the count of successful assignments returned by
194 An optional 'a' character.
195 This is used with string conversions, and relieves the caller of the
196 need to allocate a corresponding buffer to hold the input: instead,
198 allocates a buffer of sufficient size,
199 and assigns the address of this buffer to the corresponding
201 argument, which should be a pointer to a
203 variable (this variable does not need to be initialized before the call).
204 The caller should subsequently
206 this buffer when it is no longer required.
207 This is a GNU extension;
208 C99 employs the 'a' character as a conversion specifier (and
209 it can also be used as such in the GNU implementation).
212 An optional decimal integer which specifies the
213 .IR "maximum field width" .
214 Reading of characters stops either when this maximum is reached or
215 when a non-matching character is found, whichever happens first.
216 Most conversions discard initial whitespace characters (the exceptions
218 and these discarded characters don't count towards the maximum field width.
219 String input conversions store a null terminator ('\\0')
220 to mark the end of the input;
221 the maximum field width does not include this terminator.
225 .IR "type modifier character" .
228 type modifier is used with integer conversions such as
230 to specify that the corresponding
234 rather than a pointer to an
239 .I "conversion specifier"
240 that specifies the type of input conversion to be performed.
242 The conversion specifications in
244 are of two forms, either beginning with '%' or beginning with
245 "\fB%\fP\fIn\fP\fB$\fP".
246 The two forms should not be mixed in the same
248 string, except that a string containing
249 "\fB%\fP\fIn\fP\fB$\fP"
250 specifications can include
257 specifications then these correspond in order with successive
261 "\fB%\fP\fIn\fP\fB$\fP"
262 form (which is specified in POSIX.1-2001, but not C99),
264 is a decimal integer that specifies that the converted input should
265 be placed in the location referred to by the
272 .IR "type modifier characters"
273 can appear in a conversion specification:
276 Indicates that the conversion will be one of
280 and the next pointer is a pointer to a
283 .I unsigned short int
290 but the next pointer is a pointer to a
293 .IR "unsigned char" .
298 but the next pointer is a pointer to a
302 This modifier was introduced in C99.
305 Indicates either that the conversion will be one of
309 and the next pointer is a pointer to a
315 or that the conversion will be one of
317 and the next pointer is a pointer to
323 characters is equivalent to
329 the corresponding parameter is considered
330 as a pointer to a wide character or wide-character string respectively.
331 .\" This use of l was introduced in Amendment 1 to ISO C90.
334 Indicates that the conversion will be either
336 and the next pointer is a pointer to
338 or the conversion will be
340 and the next pointer is a pointer to
342 .\" MTK, Jul 05: The following is no longer true for modern
343 .\" ANSI C (i.e., C99):
344 .\" (Note that long long is not an
346 .\" type. Any program using this will not be portable to all
352 This specifier does not exist in ANSI C.
357 but the next pointer is a pointer to a
359 This modifier was introduced in C99.
364 but the next pointer is a pointer to a
366 This modifier was introduced in C99.
369 .I "conversion specifiers"
373 Matches a literal '%'.
376 in the format string matches a
377 single input '%' character.
378 No conversion is done, and assignment does not
382 Matches an optionally signed decimal integer;
383 the next pointer must be a pointer to
389 this exists only for backwards compatibility.
390 (Note: thus only in libc4.
391 In libc5 and glibc the
393 is silently ignored, causing old programs to fail mysteriously.)
396 Matches an optionally signed integer; the next pointer must be a pointer to
398 The integer is read in base 16 if it begins with
402 in base 8 if it begins with
404 and in base 10 otherwise.
405 Only characters that correspond to the base are used.
408 Matches an unsigned octal integer; the next pointer must be a pointer to
412 Matches an unsigned decimal integer; the next pointer must be a
417 Matches an unsigned hexadecimal integer; the next pointer must
426 Matches an optionally signed floating-point number; the next pointer must
447 Matches a sequence of non-white-space characters;
448 the next pointer must be a pointer to character array that is
449 long enough to hold the input sequence and the terminating null
450 character ('\\0'), which is added automatically.
451 The input string stops at white space or at the maximum field
452 width, whichever occurs first.
455 Matches a sequence of characters whose length is specified by the
456 .I maximum field width
457 (default 1); the next pointer must be a pointer to
459 and there must be enough room for all the characters (no terminating
462 The usual skip of leading white space is suppressed.
463 To skip white space first, use an explicit space in the format.
466 Matches a nonempty sequence of characters from the specified set of
467 accepted characters; the next pointer must be a pointer to
469 and there must be enough room for all the characters in the string, plus a
470 terminating null byte.
471 The usual skip of leading white space is suppressed.
472 The string is to be made up of characters in (or not in) a particular set;
473 the set is defined by the characters between the open bracket
475 character and a close bracket
480 those characters if the first character after the open bracket is a
483 To include a close bracket in the set, make it the first character after
484 the open bracket or the circumflex; any other position will end the set.
487 is also special; when placed between two other characters, it adds all
488 intervening characters to the set.
489 To include a hyphen, make it the last
490 character before the final close bracket.
494 the set "everything except close bracket, zero through nine, and hyphen".
495 The string ends with the appearance of a character not in the (or, with a
496 circumflex, in) set or when the field width runs out.
499 Matches a pointer value (as printed by
503 the next pointer must be a pointer to a pointer to
507 Nothing is expected; instead, the number of characters consumed thus far
508 from the input is stored through the next pointer, which must be a pointer
513 a conversion, although it can be suppressed with the
515 assignment-suppression character.
516 The C standard says: "Execution of a
518 directive does not increment
519 the assignment count returned at the completion of execution"
520 but the Corrigendum seems to contradict this.
522 not to make any assumptions on the effect of
524 conversions on the return value.
526 These functions return the number of input items
527 successfully matched and assigned,
528 which can be fewer than provided for,
529 or even zero in the event of an early matching failure.
533 is returned if the end of input is reached before either the first
534 successful conversion or a matching failure occurs.
536 is also returned if a read error occurs,
537 in which case the error indicator for the stream (see
541 is set indicate the error.
548 conform to C89 and C99.
552 specifier is the 4.4BSD notation for
558 in integer conversions is the GNU notation.
560 The Linux version of these functions is based on the
569 for a more concise description.
571 All functions are fully C89 conformant, but provide the
572 additional specifiers
576 as well as an additional behavior of the
581 The latter may be considered to be a bug, as it changes the
582 behavior of specifiers defined in C89.
584 Some combinations of the type modifiers and conversion
585 specifiers defined by ANSI C do not make sense
588 While they may have a well-defined behavior on Linux, this need not
589 to be so on other architectures.
590 Therefore it usually is better to use
591 modifiers that are not defined by ANSI C at all, that is, use
602 is not the same as on 4.4BSD,
603 as it may be used in float conversions equivalently to