MSL C Reference, stdio.h

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fscanf

Compatibility:

This function is compatible with the following targets:

ANSI

BeOS

EMB/RTOS

Mac OS

Palm OS

Win32

Prototype:

#include <stdio.h>

int fscanf(FILE *stream,

		const char *format, ...);

Parameters:

Parameters for this facility are:

stream

FILE *

A pointer to a FILE stream

format

const char *

A format string

Remarks:

The fscanf() function reads programmer-defined, formatted text from stream. The function operates identically to the scanf() function with the addition of the stream argument indicating the stream to read from. Refer to the scanf() function description.

If the file is opened in update mode (+) a file cannot be read from and then written to without repositioning the file using one of the file positioning functions (fseek(), fsetpos(), or rewind()) unless the last read or write reached the end-of-file.

NOTE

On embedded/ RTOS systems this function only is implemented for stdin, stdout and stderr files.

 char str[20];

the execution of

 sscanf("acdfxbe", "%[abcdef]", str);

will store acdf in str; the `x' and following characters will not be stored because the `x' is not in the scanset.

If the first character of the scanset is the circumflex, ^, then the following characters will define a set of characters such that encountering any one of them will cause reading and storing to stop; any character outside a scanset defined in this way will be accepted, we will call this an exclusionary scanset. Thus execution of

 sscanf("stuvawxyz", "%[^abcdef]", str);

will store stuv in str. If you want ^ to be part of the scanset, you cannot list it as the first character otherwise it will be interpreted as introducing the members of an exclusionary scanset. Thus %[^abc] defines the exclusionary scanset abc whereas %[a^bc] defines the scanset abc^. %[^a^bc] defines the exclusionary scanset abc^, as does %[^^abc].

If you want ] to be in the scanset, it must be the first character of the scanset, immediately following the %[ or, to be in an exclusionary scanset, immediately after the ^, for example, %[]abc] or %[^]abc]. In any other position, the ] will be interpreted as terminating the scanset.

To include the - character in the scanset, it must be either listed first (possibly after an initial ^ or last, thus for example, %[-abc], %[abc-], %[^-abc], or %[^abc-]. The C Standard explicitly states:

If a - character is in the scanlist and is not the first, nor the second where the first character is a ^, nor the last character, the behavior is implementation-defined.

MSL interprets such a use of - in a scanlist as defining a range of characters; thus, the specification %[a-z] as being the equivalent of %[abcdefghijklmnopqrstuvwxyz]. You should bear in mind that this is MSL's interpretation and such usage may be interpreted differently in other C library implementations. Note also that it is assumed that the numeric value of the character before the - is less than that of the one after. If this relationship does not hold undefined and probably unwanted effects may be experienced.

Return:

fscanf() returns the number of items read. If there is an error in reading data that is inconsistent with the format string, fscanf() sets errno to a nonzero value. fscanf() returns EOF if it reaches the end-of-file.

"errno"

"scanf"

Example of fscanf() usage.:

#include <stdio.h>
#include <stdlib.h>

int main(void)
{
	FILE *f;
	int i;
	double x;
	char c;
	
	// create a new file for output and input
	if (( f = fopen("foobar", "w+")) == NULL) {
		printf("Can't create new file.\n");
		exit(1);
	}

	// output formatted text to the file
	fprintf(f, "%d\n%f\n%c\n", 45, 983.3923, 'M');

	// go to the beginning of the file
	rewind(f);

	// read from the stream using fscanf()
	fscanf(f, "%d %lf %c", &i, &x, &c);

	// close the file
	fclose(f);

	printf("The integer read is %d.\n", i);
	printf("The floating point value is %f.\n", x);
	printf("The character is %c.\n", c);

	return 0;

}
Output:
The integer read is 45.
The floating point value is 983.392300.
The character is M.





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Last updated: August 16, 2000

stream	FILE *	A pointer to a FILE stream
format	const char *	A format string

Modifier	Description
	Length Specifiers
hh	The `hh` flag indicates that the following `d, i, o, u, x, X` or `n` conversion specifier applies to an argument that is of type `char` or `unsigned char.`
h	The `h` flag indicates that the following `d, i, o, u, x, X` or `n` conversion specifier applies to an argument that is of type `short int` or `unsigned short int.`
l	When used with integer conversion specifier, the l flag indicates long int or an unsigned long int type. When used with floating point conversion specifier, the l flag indicates a double. When used with a `c` or `s` conversion specifier, the `l` flag indicates that the corresponding argument with type pointer to `wchar_t.`
ll	When used with integer conversion specifier, the ll flag indicates that the corresponding argument is of type long long or an unsigned long long.
L	The L flag indicates that the corresponding float conversion specifier corresponds to an argument of type long double.
v	AltiVec: `A vector bool char, vector signed char or vector unsigned char` when followed by `c, d, i, o, u, x or X` A vector float, when followed by `f..`
vh hv	AltiVec: `vector short, vector unisgned short, vector bool short or vector pixel` when followed by `c, d, i, o, u, x or X`
vl lv	AltiVec: `vector long, vector unsigned long or vector bool` when followed by `c, d, i, o, u, x or X`
	Conversion Sepcifiers
d	A decimal integer is read.
i	A decimal, octal, or hexadecimal integer is read. The integer can be prefixed with a plus or minus sign (+, -), 0 for octal numbers, 0x or 0X for hexadecimal numbers.
o	An octal integer is read.
u	An unsigned decimal integer is read.
x, X	A hexadecimal integer is read.
e, E, f, g, G	A floating point number is read. The number can be in plain decimal format (e.g. 3456.483) or in scientific notation ([-]b.aaae±dd).
s	A character string is read. The input character string is considered terminated when a white space character is reached or the maximum width has been reached. The null character is appended to the end of the array.
c	A character is read. White space characters are not skipped, but read using this conversion specifier..
p	A pointer address is read. The input format should be the same as that output by the p conversion type in printf().
n	This conversion type does not read from the input stream but stores the number of characters read in its corresponding argument.
[scanset]	Input stream characters are read and filtered determined by the `scanset`. See `"Scanset,"` for a full description.

fscanf

NOTE

Input Control String and Conversion Specifiers

MSL AltiVec Extensions for Scanf

Scanset