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Manual page for SCANF(3S)

scanf, fscanf, sscanf - formatted input conversion

SYNOPSIS

#include <stdio.h>

int scanf(const char *format, ...);

int fscanf(FILE *stream, const char *format, ...);

int sscanf(char *s, const char *format, ...);

DESCRIPTION

Scanf reads from the standard input stream stdin. Fscanf reads from the named input stream. Sscanf reads from the character string s. Each function reads characters, interprets them according to a format, and stores the results in its arguments. Each expects as arguments a control string format, described below, and a set of pointer arguments indicating where the converted input should be stored.

The control string usually contains conversion specifications, which are used to direct interpretation of input sequences. The control string may contain:

1.: Blanks, tabs or newlines, which match optional white space in the input.
2.: An ordinary character (not %) which must match the next character of the input stream.
3.: Conversion specifications, consisting of the character %, an optional assignment suppressing character *, an optional numerical maximum field width, and a conversion character.

A conversion specification directs the conversion of the next input field; the result is placed in the variable pointed to by the corresponding argument, unless assignment suppression was indicated by *. An input field is defined as a string of non-space characters; it extends to the next inappropriate character or until the field width, if specified, is exhausted.

The conversion character indicates the interpretation of the input field; the corresponding pointer argument must usually be of a restricted type. The following conversion characters are legal:

%: a single `%' is expected in the input at this point; no assignment is done.
d: a decimal integer is expected; the corresponding argument should be an integer pointer.
o: an octal integer is expected; the corresponding argument should be a integer pointer.
x: a hexadecimal integer is expected; the corresponding argument should be an integer pointer.
s: a character string is expected; the corresponding argument should be a character pointer pointing to an array of characters large enough to accept the string and a terminating `\0', which will be added. The input field is terminated by a space character or a newline.
c: a character is expected; the corresponding argument should be a character pointer. The normal skip over space characters is suppressed in this case; to read the next non-space character, try `%1s'. If a field width is given, the corresponding argument should refer to a character array, and the indicated number of characters is read.
e,f,g,E,G: a floating point number is expected; the next field is converted accordingly and stored through the corresponding argument, which should be a pointer to a float. The input format for floating point numbers is an optionally signed string of digits possibly containing a decimal point, followed by an optional exponent field consisting of an E or e followed by an optionally signed integer.
[: indicates a string not to be delimited by space characters. The left bracket is followed by a set of characters and a right bracket; the characters between the brackets define a set of characters making up the string. If the first character is not circumflex (^), the input field is all characters until the first character not in the set between the brackets; if the first character after the left bracket is ^, the input field is all characters until the first character which is in the remaining set of characters between the brackets. The corresponding argument must point to a character array.

p: indicates a hexadecimal value as produced by the %p pointer conversion of the printf-family of functions. The corresponding argument must be a pointer to a pointer to void. The result is only valid for a pointer converted during the same program execution.
n: No input is consumed. The argument must be a pointer to integer into which the number of characters read from the input stream so far is written. A %n directive does not increment the assignment count returned at the completion of the function.

The conversion characters d, o and x may be capitalized or preceded by l to indicate that a pointer to long rather than to int is in the argument list. Similarly, the conversion characters e or f may be capitalized or preceded by l to indicate a pointer to double rather than to float. The conversion characters d, o and x may be preceded by h to indicate a pointer to short rather than to int.

The scanf functions return the number of successfully matched and assigned input items. This can be used to decide how many input items were found. The constant EOF is returned upon end of input; note that this is different from 0, which means that no conversion was done; if conversion was intended, it was frustrated by an inappropriate character in the input.

EXAMPLES

For example, the call

: int i; float x; char name[50];
scanf("%d%f%s", &i, &x, name);

with the input line

: 25 54.32E-1 thompson

will assign to i the value 25, x the value 5.432, and name will contain `thompson\0'. Or,

: int i; float x; char name[50];
scanf("%2d%f%*d%[1234567890]", &i, &x, name);

with input

: 56789 0123 56a72

will assign 56 to i, 789.0 to x, skip `0123', and place the string `56\0' in name. The next call to getchar will return `a'.

RETURN VALUE

Scanf, fscanf, and sscanf return EOF if an input failure occurs before any conversion. Otherwise, the number of input items assigned, which can be fewer than provided for, is returned.

ERRORS

The underlying function of scanf, fscanf, and sscanf is read (2). The error conditions specified for read (2) apply to scanf, fscanf, and sscanf.

BUGS

The success of literal matches and suppressed assignments is not directly determinable.