Subversion Repositories planix.SVN

.TH FSCANF 2

.SH NAME

fscanf, scanf, sscanf, vfscanf \- scan formatted input

.SH SYNOPSIS

.B "#include <u.h>

.br

.B "#include <stdio.h>"

.PP

.B

int fscanf(FILE *f, char *format, ...)

.PP

.B

int scanf(char *format, ... )

.PP

.B

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

.PP

.B

int vfscanf(FILE *stream, char *format, char *args)

.SH DESCRIPTION

.I Fscanf

reads from the named input stream

.I f

(see

.IR fopen (2))

under control of the string pointed to by

.I format

that specifies the admissible input sequences and how they are to be converted

for assignment, using subsequent arguments as pointers to the objects

to receive the converted input.

If there are insufficient arguments for the format, the behavior is undefined.

If the format is exhausted while arguments remain, the excess arguments

are evaluated (as always) but are otherwise ignored.

.PP

.I Scanf

and

.I sscanf

are the same, but they read from

.I stdin

and the character string

.IR s ,

respectively.

.I Vfscanf

is like

.IR scanf ,

except the

.I args

argument is a pointer to an argument in an argument list of the

calling function and the effect is as if the calling function's

argument list from that point on is passed to the scanf routines.

.PP

The format is composed of zero or more directives:

one or more white-space characters; an ordinary character (not

.BR % );

or a conversion specification.

Each conversion specification is introduced by the character

.BR %.

After the

.BR % ,

the following appear in sequence:

.PP

.RS

An optional assignment-suppressing character

.BR * .

.PP

An optional decimal integer that specifies the maximum field width.

.PP

An optional

.BR h ,

.B l

(ell) or

.B L

indicating the size of the receiving object.

The conversion specifiers

.BR d ,

.BR i ,

and

.B n

shall be preceded by

.B h

if the corresponding argument is a pointer to

.B short

rather than a pointer to

.BR int ,

or by

.B l

if it is a pointer to

.BR long .

Similarly, the conversion specifiers

.BR o ,

.BR u ,

and

.B x

shall be preceded by

.B h

if the corresponding argument is a pointer to

.B unsigned

.B short

rather than a pointer to

.BR unsigned ,

or by

.B l

if it is a pointer to

.B unsigned

.BR long .

Finally, the conversion specifiers

.BR e ,

.BR f ,

and

.B g

shall be preceded by

.B l

if the corresponding argument is a pointer to

.B double

rather than a pointer to

.BR float ,

or by

.B L

if it is a pointer to

.B long

.BR double .

If an

.BR h ,

.BR l ,

or

.B L

appears with any other conversion specifier, the behavior is undefined.

.PP

A character that specifies the type of conversion to be applied.

The valid conversion specifiers are described below.

.RE

.PP

.I Fscanf

executes each directive of the format in turn.

If a directive fails, as detailed below,

.I fscanf

returns.

Failures are described as input failures (due to the unavailability

of input),

or matching failures (due to inappropriate input).

.PP

A directive composed of white space is executed by reading input up

to the first non-white-space character (which remains unread),

or until no more characters can be read.

.PP

A directive that is an ordinary character is executed by reading

the next character from the stream.

If if differs from the one comprising the directive,

the directive fails, and the differing and subsequent characters

remain unread.

.PP

A directive that is a conversion specification defines a set of

matching input sequences, as described below for each specifier.

A conversion specification is executed in the following steps:

.PP

Input white-space characters (as specified by

.IR isspace ,

see

.IR ctype (2))

are skipped, unless the specification includes a

.BR [ ,

.BR c ,

or

.B n

specifier.

.PP

An input item is read from the stream,

unless the specification includes an

.B n

specifier.

An input item is defined as the longest sequence of input characters

(up to any specified maximum field width) which is an initial

subsequence of a matching sequence.

The first character, if any, after the input item remains unread.

If the length of the input item is zero, the execution of

the directive fails: this condition is a matching failure,

unless an error prevented input from the stream,

in which case it is an input failure.

.PP

Except in the case of a

.B %

specifier, the input item (or, in the case of a

.B %n

directive, the count of input characters)

is converted to a type appropriate to the conversion specifier.

If the input item is not a matching sequence, the execution of

the directive fails: this condition is a matching failure.

Unless assignment suppression was indicated by a

.BR * ,

the result of the conversion is placed in the object pointed to by the

first argument following the

.I format

argument that has not already received a conversion result.

If this object does not have an appropriate type,

or if the result of the conversion cannot be represented

in the space provided, the behavior is undefined.

.PP

The following conversion specifiers are valid:

.TP 6

.B d

Matches an optionally signed decimal integer,

whose format is the same as expected for the subject sequence

of the

.I strtol

(see

.IR atof (2))

function with 10 for the

.B base

argument.

The corresponding argument shall be a pointer to

.BR int .

.TP

.B i

Matches an optionally signed decimal integer,

whose format is the same as expected for the subject sequence

of the

.I strtol

function with 0 for the

.B base

argument.

The corresponding argument shall be a pointer to

.BR int .

.TP

.B o

Matches an optionally signed octal integer,

whose format is the same as expected for the subject sequence

of the

.I strtoul

(see

.IR atof (2))

function with 8 for the

.B base

argument.

The corresponding argument shall be a pointer to

.B unsigned

.BR int .

.TP

.B u

Matches an optionally signed decimal integer,

whose format is the same as expected for the subject sequence

of the

.I strtoul

function with 10 for the

.B base

argument.

The corresponding argument shall be a pointer to

.B unsigned

.BR int .

.TP

.B x

Matches an optionally signed hexadecimal integer,

whose format is the same as expected for the subject sequence

of the

.I strtoul

function with 16 for the

.B base

argument.

The corresponding argument shall be a pointer to

.B unsigned

.BR int .

.TP

.BR e , f , g

Matches an optionally signed floating-point number, whose format is

the same as expected for the subject string of the

.I strtod

(see

.IR atof (2))

function.

The corresponding argument shall be a pointer to

.BR float .

.TP

.B s

Matches a sequence of non-white-space characters.

The corresponding argument shall be a pointer to the initial

character of an array large enough to accept the sequence

and a terminating NUL (0) character, which will be added automatically.

.TP

.B [

Matches a nonempty sequence of characters from a set of expected

characters (the

.IR scanset ).

The corresponding argument shall be a pointer to the initial

character of an array large enough to accept the sequence and a terminating

NUL character, which will be added automatically.

The conversion specifier includes all subsequent characters in the

.I format

string, up to and including the matching right brace

.RB ( ] ).

The characters between the brackets (the

.IR scanlist )

comprise the scanset, unless the character after the left bracket

is a circumflex

.RB ( ^ ),

in which case the scanset contains all characters that do not appear

in the scanlist between the circumflex and the right bracket.

As a special case, if the conversion specifier begins with

.B []

or

.BR [^] ,

the right bracket character is in the scanlist and the next

right bracket character is the matching right bracket

that ends the specification.

If a

.B -

character is in the scanlist and is not the first, nor the second

where the first character is a

.BR ^ ,

nor the last character, the behavior is implementation-defined

(in Plan 9: the scanlist includes all characters in the

.SM ASCII

(sic)

range between the two characters on either side of the

.BR - ).

.TP

.B c

Matches a sequence of characters of the number specified by the field width

(1 if no field width is present in the directive).

The corresponding argument shall be a pointer to the initial character

of an array large enough to accept the sequence.

No NUL character is added.

.TP

.B P

Matches an implementation-defined set of sequences,

which should be the same as the set of sequences that may be

produced by the

.B %P

conversion of the

.IR fprintf (2)

function

(in Plan 9, a hexadecimal number).

The corresponding argument shall be a pointer to a pointer to

.BR void .

The interpretation of the input item is implementation defined;

however, for any input item other than a value converted earlier

during the same program execution, the behavior of the

.B %P

conversion is undefined.

.TP

.B n

No input is consumed.

The corresponding argument shall be a pointer to integer into which

is written the number of characters read from the input stream so far

by this call to

.IR fscanf .

Execution of a

.B %n

directive does not increment the assignment count returned at the

completion of

.IR fscanf .

.TP

.B %

Matches a single

.BR % ;

no conversion or assignment occurs.

The complete conversion specification shall be

.BR %% .

.PD

.PP

If a conversion specification is invalid, the behavior is undefined.

.PP

The conversion specifiers

.BR E ,

.BR G ,

and

.B X

are also valid and behave the same as, respectively,

.BR e ,

.BR g ,

and

.BR x .

.PP

If end-of-file is encountered during input, conversion is terminated.

If end-of-file occurs before any characters matching the current

directive have been read (other than leading white space,

where permitted), execution of the current directive terminates with

an input failure;

otherwise, unless execution of the current directive is terminated

with a matching failure, execution of the following directive

(if any) is terminated with an input failure.

.PP

If conversion terminates on a conflicting input character,

the offending input character is left unread in the input stream.

Trailing white space (including newline characters) is left unread

unless matched by a directive.

The success of literal matches and suppressed assignments is not

directly determinable other than via the

.B %n

directive.

.PP

The return value from

.I fscanf

is the number of input items assigned, which can be fewer than

provided for, or even zero, in the event of an early matching failure.

However, if an input failure occurs before any conversion,

.B EOF

is returned.

.SH SOURCE

.B /sys/src/libstdio

.SH "SEE ALSO"

.IR fopen (2),

.IR fgetc (2)

.SH BUGS

Does not know about

.SM UTF.