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vfscanf

NAME

vfscanf - Format input of a stdarg argument list.

SYNOPSIS
#include <stdio.h>

int vfscanf(FILE *restrict stream, const char *restrict format, va_list arg);
DESCRIPTION

The vfscanf function is equivalent to the fscanf function except that instead of being called with a variable number of arguments, it is called with an argument list as defined in the stdarg header. This function shall not invoke the va_end macro. As this function invokes the va_arg macro, the value of ap after the return is unspecified.

PARAMETERS

  • stream - Pointer to an open file.

  • format - String that can contain one or more of these items:

Whitespace characters

the function will read and ignore any whitespace characters (this includes blank, newline and tab characters) encountered before the next non-whitespace character. This includes any quantity of whitespace characters (including none).

Non-whitespace characters

(any character not including blank, newline, tab, or any format specifier beginning with % character): this cause that the function read and discard any character that match the given non-whitespace character. If this character is not found the function ends returning error.

Format specifiers

A sequence of characters begining with % indicates that next data has to be read and stored at the location pointed by its corresponding argument with a given format that is specified following this prototype: %[*][width][modifiers]type where:

*

Data is read but ignored. It is not assigned to the corresponding argument.

width

Specifies the maximum number of characters to be read.

modifiers

Specifies a different size for the data pointed by argument:

  • h: short int

  • l: long int (if integer) or double (if floating point).

  • L: long double

type

Character specifying the type of data that is expected and how it has to be read. See next table.
type qualifying input required argument

c

Single character: Reads the next character (whitespace characters included).

char *

d

Decimal integer: Number optionally prepended with a sign.

int *

e,E,f,g,G

Floating point: Decimal number containing a decimal point, optionally prepended by a sign and optionally followed by the e or E character and a decimal number. Valid entries are -732.103 or 7.12e4

float *

o

Octal integer.

int *

s

String of characters. This will read subsequent characters until a whitespace is found (whitespace characters are blank, newline and tab).

char *(string)

u

Unsigned decimal integer.

unsigned int *

x

Hexadecimal integer.

int *

argument(s) - pointer to objects or structures to be filled with data read as specified by format string. There must be the same number of these parameters than the number of format tags. NOTE: These arguments must be pointers: if you want to store the result of a scanf operation on a standard variable you should precede it with the reference operator, i.e. an ampersand sign: &

RETURN VALUE

The vfscanf function returns the value of the macro EOF if an input failure occurs before any conversion. Otherwise, the vfscanf function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure.

SEE ALSO

fscanf

EXAMPLE
link:src/vfscanf.c[role=include]
OUTPUT
$ gcc -Wall vfscanf.c
$ cat file.txt
Hello 42w123.456789

$ ./a.out file.txt
string = Hello
long double = 42
char = w
float = 123.456787