/* Void Main's man pages */
{ phpMan } else { main(); }
SCANF(3) Linux Programmer's Manual SCANF(3)
NAME
scanf, fscanf, sscanf, vscanf, vsscanf, vfscanf - input format conversion
SYNOPSIS
#include <stdio.h>
int scanf(const char *format, ...);
int fscanf(FILE *stream, const char *format, ...);
int sscanf(const char *str, const char *format, ...);
#include <stdarg.h>
int vscanf(const char *format, va_list ap);
int vsscanf(const char *str, const char *format, va_list ap);
int vfscanf(FILE *stream, const char *format, va_list ap);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
vscanf(), vsscanf(), vfscanf(): _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE; or cc -std=c99
DESCRIPTION
The scanf() family of functions scans input according to format as described below. This format may contain conversion
specifications; the results from such conversions, if any, are stored in the locations pointed to by the pointer argu-
ments that follow format. Each pointer argument must be of a type that is appropriate for the value returned by the cor-
responding conversion specification.
If the number of conversion specifications in format exceeds the number of pointer arguments, the results are undefined.
If the number of pointer arguments exceeds the number of conversion specifications, then the excess pointer arguments are
evaluated, but are otherwise ignored.
The scanf() function reads input from the standard input stream stdin, fscanf() reads input from the stream pointer
stream, and sscanf() reads its input from the character string pointed to by str.
The vfscanf() function is analogous to vfprintf(3) and reads input from the stream pointer stream using a variable argu-
ment list of pointers (see stdarg(3). The vscanf() function scans a variable argument list from the standard input and
the vsscanf() function scans it from a string; these are analogous to the vprintf(3) and vsprintf(3) functions respec-
tively.
The format string consists of a sequence of directives which describe how to process the sequence of input characters.
If processing of a directive fails, no further input is read, and scanf() returns. A "failure" can be either of the fol-
lowing: input failure, meaning that input characters were unavailable, or matching failure, meaning that the input was
inappropriate (see below).
A directive is one of the following:
o A sequence of white-space characters (space, tab, newline, etc.; see isspace(3)). This directive matches any
amount of white space, including none, in the input.
o An ordinary character (i.e., one other than white space or '%'). This character must exactly match the next char-
acter of input.
o A conversion specification, which commences with a '%' (percent) character. A sequence of characters from the
input is converted according to this specification, and the result is placed in the corresponding pointer argu-
ment. If the next item of input does not match the conversion specification, the conversion fails -- this is a
matching failure.
Each conversion specification in format begins with either the character '%' or the character sequence "%n$" (see below
for the distinction) followed by:
o An optional '*' assignment-suppression character: scanf() reads input as directed by the conversion specification,
but discards the input. No corresponding pointer argument is required, and this specification is not included in
the count of successful assignments returned by scanf().
o An optional 'a' character. This is used with string conversions, and relieves the caller of the need to allocate
a corresponding buffer to hold the input: instead, scanf() allocates a buffer of sufficient size, and assigns the
address of this buffer to the corresponding pointer argument, which should be a pointer to a char * variable (this
variable does not need to be initialized before the call). The caller should subsequently free(3) this buffer
when it is no longer required. This is a GNU extension; C99 employs the 'a' character as a conversion specifier
(and it can also be used as such in the GNU implementation).
o An optional decimal integer which specifies the maximum field width. Reading of characters stops either when this
maximum is reached or when a nonmatching character is found, whichever happens first. Most conversions discard
initial white space characters (the exceptions are noted below), and these discarded characters don't count
towards the maximum field width. String input conversions store a null terminator ('\0') to mark the end of the
input; the maximum field width does not include this terminator.
o An optional type modifier character. For example, the l type modifier is used with integer conversions such as %d
to specify that the corresponding pointer argument refers to a long int rather than a pointer to an int.
o A conversion specifier that specifies the type of input conversion to be performed.
The conversion specifications in format are of two forms, either beginning with '%' or beginning with "%n$". The two
forms should not be mixed in the same format string, except that a string containing "%n$" specifications can include %%
and %*. If format contains '%' specifications then these correspond in order with successive pointer arguments. In the
"%n$" form (which is specified in POSIX.1-2001, but not C99), n is a decimal integer that specifies that the converted
input should be placed in the location referred to by the n-th pointer argument following format.
Conversions
The following type modifier characters can appear in a conversion specification:
h Indicates that the conversion will be one of d, i, o, u, x, X, or n and the next pointer is a pointer to a short
int or unsigned short int (rather than int).
hh As for h, but the next pointer is a pointer to a signed char or unsigned char.
j As for h, but the next pointer is a pointer to an intmax_t or a uintmax_t. This modifier was introduced in C99.
l Indicates either that the conversion will be one of d, i, o, u, x, X, or n and the next pointer is a pointer to a
long int or unsigned long int (rather than int), or that the conversion will be one of e, f, or g and the next
pointer is a pointer to double (rather than float). Specifying two l characters is equivalent to L. If used with
%c or %s the corresponding parameter is considered as a pointer to a wide character or wide-character string
respectively.
L Indicates that the conversion will be either e, f, or g and the next pointer is a pointer to long double or the
conversion will be d, i, o, u, or x and the next pointer is a pointer to long long.
q equivalent to L. This specifier does not exist in ANSI C.
t As for h, but the next pointer is a pointer to a ptrdiff_t. This modifier was introduced in C99.
z As for h, but the next pointer is a pointer to a size_t. This modifier was introduced in C99.
The following conversion specifiers are available:
% Matches a literal '%'. That is, %% in the format string matches a single input '%' character. No conversion is
done (but initial white space characters are discarded), and assignment does not occur.
d Matches an optionally signed decimal integer; the next pointer must be a pointer to int.
D Equivalent to ld; this exists only for backwards compatibility. (Note: thus only in libc4. In libc5 and glibc
the %D is silently ignored, causing old programs to fail mysteriously.)
i Matches an optionally signed integer; the next pointer must be a pointer to int. The integer is read in base 16
if it begins with 0x or 0X, in base 8 if it begins with 0, and in base 10 otherwise. Only characters that corre-
spond to the base are used.
o Matches an unsigned octal integer; the next pointer must be a pointer to unsigned int.
u Matches an unsigned decimal integer; the next pointer must be a pointer to unsigned int.
x Matches an unsigned hexadecimal integer; the next pointer must be a pointer to unsigned int.
X Equivalent to x.
f Matches an optionally signed floating-point number; the next pointer must be a pointer to float.
e Equivalent to f.
g Equivalent to f.
E Equivalent to f.
a (C99) Equivalent to f.
s Matches a sequence of non-white-space characters; the next pointer must be a pointer to character array that is
long enough to hold the input sequence and the terminating null character ('\0'), which is added automatically.
The input string stops at white space or at the maximum field width, whichever occurs first.
c Matches a sequence of characters whose length is specified by the maximum field width (default 1); the next
pointer must be a pointer to char, and there must be enough room for all the characters (no terminating null byte
is added). The usual skip of leading white space is suppressed. To skip white space first, use an explicit space
in the format.
[ Matches a nonempty sequence of characters from the specified set of accepted characters; the next pointer must be
a pointer to char, and there must be enough room for all the characters in the string, plus a terminating null
byte. The usual skip of leading white space is suppressed. The string is to be made up of characters in (or not
in) a particular set; the set is defined by the characters between the open bracket [ character and a close
bracket ] character. The set excludes those characters if the first character after the open bracket is a circum-
flex (^). To include a close bracket in the set, make it the first character after the open bracket or the cir-
cumflex; any other position will end the set. The hyphen character - is also special; when placed between two
other characters, it adds all intervening characters to the set. To include a hyphen, make it the last character
before the final close bracket. For instance, [^]0-9-] means the set "everything except close bracket, zero
through nine, and hyphen". The string ends with the appearance of a character not in the (or, with a circumflex,
in) set or when the field width runs out.
p Matches a pointer value (as printed by %p in printf(3); the next pointer must be a pointer to a pointer to void.
n Nothing is expected; instead, the number of characters consumed thus far from the input is stored through the next
pointer, which must be a pointer to int. This is not a conversion, although it can be suppressed with the *
assignment-suppression character. The C standard says: "Execution of a %n directive does not increment the
assignment count returned at the completion of execution" but the Corrigendum seems to contradict this. Probably
it is wise not to make any assumptions on the effect of %n conversions on the return value.
RETURN VALUE
These functions return the number of input items successfully matched and assigned, which can be fewer than provided for,
or even zero in the event of an early matching failure.
The value EOF is returned if the end of input is reached before either the first successful conversion or a matching
failure occurs. EOF is also returned if a read error occurs, in which case the error indicator for the stream (see fer-
ror(3)) is set, and errno is set indicate the error.
ERRORS
EAGAIN The file descriptor underlying stream is marked nonblocking, and the read operation would block.
EBADF The file descriptor underlying stream is invalid, or not open for reading.
EILSEQ Input byte sequence does not form a valid character.
EINTR The read operation was interrupted by a signal; see signal(7).
EINVAL Not enough arguments; or format is NULL.
ENOMEM Out of memory.
ERANGE The result of an integer conversion would exceed the size that can be stored in the corresponding integer type.
CONFORMING TO
The functions fscanf(), scanf(), and sscanf() conform to C89 and C99 and POSIX.1-2001. These standards do not specify
the ERANGE error.
The q specifier is the 4.4BSD notation for long long, while ll or the usage of L in integer conversions is the GNU nota-
tion.
The Linux version of these functions is based on the GNU libio library. Take a look at the info documentation of GNU
libc (glibc-1.08) for a more concise description.
NOTES
The GNU C library supports a nonstandard extension that causes the library to dynamically allocate a string of sufficient
size for input strings for the %s and %a[range] conversion specifiers. To make use of this feature, specify a as a
length modifier (thus %as or %a[range]). The caller must free(3) the returned string, as in the following example:
char *p;
int n;
errno = 0;
n = scanf("%a[a-z]", &p);
if (n == 1) {
printf("read: %s\n", p);
free(p);
} else if (errno != 0) {
perror("scanf");
} else {
fprintf(stderr, "No matching characters\n"):
}
As shown in the above example, it is only necessary to call free(3) if the scanf() call successfully read a string.
The a modifier is not available if the program is compiled with gcc -std=c99 or gcc -D_ISOC99_SOURCE (unless _GNU_SOURCE
is also specified), in which case the a is interpreted as a specifier for floating-point numbers (see above).
Since version 2.7, glibc also provides the m modifier for the same purpose as the a modifier. The m modifier has the
following advantages:
* It may also be applied to %c conversion specifiers (e.g., %3mc).
* It avoids ambiguity with respect to the %a floating-point conversion specifier (and is unaffected by gcc -std=c99 etc.)
* It is specified in the upcoming revision of the POSIX.1 standard.
BUGS
All functions are fully C89 conformant, but provide the additional specifiers q and a as well as an additional behavior
of the L and l specifiers. The latter may be considered to be a bug, as it changes the behavior of specifiers defined in
C89.
Some combinations of the type modifiers and conversion specifiers defined by ANSI C do not make sense (e.g. %Ld). While
they may have a well-defined behavior on Linux, this need not to be so on other architectures. Therefore it usually is
better to use modifiers that are not defined by ANSI C at all, that is, use q instead of L in combination with d, i, o,
u, x, and X conversions or ll.
The usage of q is not the same as on 4.4BSD, as it may be used in float conversions equivalently to L.
SEE ALSO
getc(3), printf(3), setlocale(3), strtod(3), strtol(3), strtoul(3)
COLOPHON
This page is part of release 3.25 of the Linux man-pages project. A description of the project, and information about
reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.
GNU 2008-07-12 SCANF(3)
