int scanf( const char *format, ... );
(until C99)int scanf( const char *restrict format, ... );
(since C99) (2) int fscanf( FILE *stream, const char *format, ... ); (until C99) int fscanf( FILE *restrict stream, const char *restrict format, ... ); (since C99) (3)int sscanf( const char *buffer, const char *format, ... );
(until C99)int sscanf( const char *restrict buffer, const char *restrict format, ... );
(since C99)int scanf_s(const char *restrict format, ...);
(4) (since C11) int fscanf_s(FILE *restrict stream, const char *restrict format, ...); (5) (since C11)int sscanf_s(const char *restrict buffer, const char *restrict format, ...);
(6) (since C11)Reads data from a variety of sources, interprets it according to format and stores the results into given locations.
reads the data from
stdin2) reads the data from file stream stream
3) reads the data from null-terminated character string buffer. Reaching the end of the string is equivalent to reaching the end-of-file condition for fscanf
Same as
(1-3), except that
%c,
%s, and
%[conversion specifiers each expect two arguments (the usual pointer and a value of type
rsize_tindicating the size of the receiving array, which may be
1when reading with a
%cinto a single char) and except that the following errors are detected at runtime and call the currently installed
constraint handlerfunction:
format, stream, or buffer is a null pointerrsize_t) argument provided for each of those conversion specifiersscanf_s, fscanf_s, and sscanf_s are only guaranteed to be available if __STDC_LIB_EXT1__ is defined by the implementation and if the user defines __STDC_WANT_LIB_EXT1__ to the integer constant 1 before including <stdio.h>.
The format string consists of
The following format specifiers are available:
Conversionhh h none l ll j z t L Only available since C99â Yes Yes Yes Yes Yes %
Matches literal %.
c
Matches a character or a sequence of characters.
char*
wchar_t*
N/A N/A N/A N/A N/As
Matches a sequence of non-whitespace characters (a string).
[set ]
Matches a non-empty sequence of character from set of characters.
^, then all characters not in the set are matched.] or ^] then the ] character is also included into the set.- in the non-initial position in the scanset may be indicating a range, as in [0-9].d
Matches a decimal integer.
signed char* or unsigned char*
signed short* or unsigned short*
signed int* or unsigned int*
signed long* or unsigned long*
signed long long* or unsigned long long*
intmax_t*or
uintmax_t* size_t* ptrdiff_t* N/Ai
Matches an integer.
u
Matches an unsigned decimal integer.
o
Matches an unsigned octal integer.
x
X
Matches an unsigned hexadecimal integer.
n
Returns the number of characters read so far.
a (C99)
A (C99)
e
E
f
F (C99)
g
G
Matches a floating-point number.
float*
double*
N/A N/A N/A N/Along double*
p
Matches implementation defined character sequence defining a pointer.
printf family of functions should produce the same sequence using %p format specifier.void**
N/A N/A N/A N/A N/A N/A NotesFor every conversion specifier other than n, the longest sequence of input characters which does not exceed any specified ï¬eld width and which either is exactly what the conversion specifier expects or is a prefix of a sequence it would expect, is what's consumed from the stream. The ï¬rst character, if any, after this consumed sequence remains unread. If the consumed sequence has length zero or if the consumed sequence cannot be converted as specified above, the matching failure occurs unless end-of-ï¬le, an encoding error, or a read error prevented input from the stream, in which case it is an input failure.
All conversion specifiers other than [, c, and n consume and discard all leading whitespace characters (determined as if by calling isspace) before attempting to parse the input. These consumed characters do not count towards the specified maximum field width.
The conversion specifiers lc, ls, and l[ perform multibyte-to-wide character conversion as if by calling mbrtowc with an mbstate_t object initialized to zero before the first character is converted.
The conversion specifiers s and [ always store the null terminator in addition to the matched characters. The size of the destination array must be at least one greater than the specified field width. The use of %s or %[, without specifying the destination array size, is as unsafe as gets.
The correct conversion specifications for the fixed-width integer types (int8_t, etc) are defined in the header <inttypes.h> (although SCNdMAX, SCNuMAX, etc is synonymous with %jd, %ju, etc).
There is a sequence point after the action of each conversion specifier; this permits storing multiple fields in the same âsinkâ variable.
When parsing an incomplete floating-point value that ends in the exponent with no digits, such as parsing "100er" with the conversion specifier %f, the sequence "100e" (the longest prefix of a possibly valid floating-point number) is consumed, resulting in a matching error (the consumed sequence cannot be converted to a floating-point number), with "r" remaining. Some existing implementations do not follow this rule and roll back to consume only "100", leaving "er", e.g., glibc bug 1765.
If a conversion specification is invalid, the behavior is undefined.
If a conversion specification is invalid, the behavior is undefined.
[edit] Return value 1-3)Number of receiving arguments successfully assigned (which may be zero in case a matching failure occurred before the first receiving argument was assigned), or
EOFif input failure occurs before the first receiving argument was assigned.
4-6)Same as
(1-3), except that
EOFis also returned if there is a runtime constraint violation.
[edit] ComplexityNot guaranteed. Notably, some implementations of sscanf are O(N), where N = strlen(buffer) [1].
Because most conversion specifiers first consume all consecutive whitespace, code such as
scanf("%d", &a);
scanf("%d", &b);
will read two integers that are entered on different lines (second %d will consume the newline left over by the first) or on the same line, separated by spaces or tabs (second %d will consume the spaces or tabs).
The conversion specifiers that do not consume leading whitespace, such as
%c, can be made to do so by using a whitespace character in the format string:
scanf("%d", &a);
scanf(" %c", &c); // consume all consecutive whitespace after %d, then read a char[edit] Example
#define __STDC_WANT_LIB_EXT1__ 1
#include <stdio.h>
#include <stddef.h>
#include <locale.h>
int main(void)
{
int i, j;
float x, y;
char str1[10], str2[4];
wchar_t warr[2];
setlocale(LC_ALL, "en_US.utf8");
char input[] = "25 54.32E-1 Thompson 56789 0123 56Ãæ°´";
/* parse as follows:
%d: an integer
%f: a floating-point value
%9s: a string of at most 9 non-whitespace characters
%2d: two-digit integer (digits 5 and 6)
%f: a floating-point value (digits 7, 8, 9)
%*d: an integer which isn't stored anywhere
' ': all consecutive whitespace
%3[0-9]: a string of at most 3 decimal digits (digits 5 and 6)
%2lc: two wide characters, using multibyte to wide conversion */
int ret = sscanf(input, "%d%f%9s%2d%f%*d %3[0-9]%2lc",
&i, &x, str1, &j, &y, str2, warr);
printf("Converted %d fields:\n"
"i = %d\n"
"x = %f\n"
"str1 = %s\n"
"j = %d\n"
"y = %f\n"
"str2 = %s\n"
"warr[0] = U+%x\n"
"warr[1] = U+%x\n",
ret, i, x, str1, j, y, str2, warr[0], warr[1]);
#ifdef __STDC_LIB_EXT1__
int n = sscanf_s(input, "%d%f%s", &i, &x, str1, (rsize_t)sizeof str1);
// writes 25 to i, 5.432 to x, the 9 bytes "Thompson\0" to str1, and 3 to n.
#endif
}
Possible output:
Converted 7 fields: i = 25 x = 5.432000 str1 = Thompson j = 56 y = 789.000000 str2 = 56 warr[0] = U+df warr[1] = U+6c34[edit] References
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