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X-Hacker.org- Watcom C/C++ v10.0 : C library - <b>synopsis:</b>
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Synopsis:
#include <stdio.h>
int scanf( const char *format, ... );
Description:
The scanf function scans input from the file designated by stdin under
control of the argument format. The format string is described below.
Following the format string is the list of addresses of items to
receive values.
Returns:
The scanf function returns EOF when the scanning is terminated by
reaching the end of the input stream. Otherwise, the number of input
arguments for which values were successfully scanned and stored is
returned.
See Also:
cscanf, fscanf, sscanf, vcscanf, vfscanf, vscanf, vsscanf
Example:
To scan a date in the form "Saturday April 18 1987":
#include <stdio.h>
void main()
{
int day, year;
char weekday[10], month[12];
scanf( "%s %s %d %d", weekday, month, &day, &year );
}
Format Control String:
The format control string consists of zero or more format directives
that specify acceptable input file data. Subsequent arguments are
pointers to various types of objects that are assigned values as the
format string is processed.
A format directive can be a sequence of one or more white-space
characters, an ordinary character, or a conversion specifier. An
ordinary character in the format string is any character, other than a
white-space character or the percent character (%), that is not part of
a conversion specifier. A conversion specifier is a sequence of
characters in the format string that begins with a percent character (%)
and is followed, in sequence, by the following:
* an optional assignment suppression indicator: the asterisk
character (*)
* an optional decimal integer that specifies the maximum field width
to be scanned for the conversion
* an optional pointer-type specification: one of "N" or "F"
* an optional type length specification: one of "h", "l" or "L"
* a character that specifies the type of conversion to be performed:
one of the characters cdefgionpsux[
As each format directive in the format string is processed, the
directive may successfully complete, fail because of a lack of input
data, or fail because of a matching error as defined by the particular
directive. If end-of-file is encountered on the input data before any
characters that match the current directive have been processed (other
than leading white-space where permitted), the directive fails for lack
of data. If end-of-file occurs after a matching character has been
processed, the directive is completed (unless a matching error occurs),
and the function returns without processing the next directive. If a
directive fails because of an input character mismatch, the character is
left unread in the input stream. Trailing white-space characters,
including new-line characters, are not read unless matched by a
directive. When a format directive fails, or the end of the format
string is encountered, the scanning is completed and the function
returns.
When one or more white-space characters (space " ", horizontal tab "\t",
vertical tab "\v", form feed "\f", carriage return "\r", new line or
linefeed "\n") occur in the format string, input data up to the first
non-white-space character is read, or until no more data remains. If no
white-space characters are found in the input data, the scanning is
complete and the function returns.
An ordinary character in the format string is expected to match the same
character in the input stream.
A conversion specifier in the format string is processed as follows:
* for conversion types other than "[", "c" and "n", leading
white-space characters are skipped
* for conversion types other than "n", all input characters, up to any
specified maximum field length, that can be matched by the
conversion type are read and converted to the appropriate type of
value; the character immediately following the last character to be
matched is left unread; if no characters are matched, the format
directive fails
* unless the assignment suppression indicator ("*") was specified, the
result of the conversion is assigned to the object pointed to by the
next unused argument (if assignment suppression was specified, no
argument is skipped); the arguments must correspond in number, type
and order to the conversion specifiers in the format string
A pointer-type specification is used to indicate the type of pointer
used to locate the next argument to be scanned:
F
pointer is a far pointer
N
pointer is a near pointer
The pointer type defaults to that used for data in the memory model for
which the program has been compiled.
A type length specifier affects the conversion as follows:
* "h" causes a "d", "i", "o", "u" or "x" (integer) conversion to
assign the converted value to an object of type short int or
unsigned short int
* "h" causes an "f" conversion to assign a fixed-point number to an
object of type long consisting of a 16-bit integer part and a 16-bit
fractional part.
* "h" causes an "n" (read length assignment) operation to assign the
number of characters that have been read to an object of type
unsigned short int
* "l" causes a "d", "i", "o", "u" or "x" (integer) conversion to
assign the converted value to an object of type long int or unsigned
long int
* "l" causes an "n" (read length assignment) operation to assign the
number of characters that have been read to an object of type
unsigned long int
* "l" causes an "e", "f" or "g" (floating-point) conversion to assign
the converted value to an object of type double
* "L" causes an "e", "f" or "g" (floating-point) conversion to assign
the converted value to an object of type long double
The valid conversion type specifiers are:
c
Any sequence of characters in the input stream of the length
specified by the field width, or a single character if no field
width is specified, is matched. The argument is assumed to point to
the first element of a character array of sufficient size to contain
the sequence, without a terminating null character ('\0'). For a
single character assignment, a pointer to a single object of type
char is sufficient.
d
A decimal integer, consisting of an optional sign, followed by one
or more decimal digits, is matched. The argument is assumed to
point to an object of type int.
e, f, g
A floating-point number, consisting of an optional sign ("+" or
"-"), followed by one or more decimal digits, optionally containing
a decimal-point character, followed by an optional exponent of the
form "e" or "E", an optional sign and one or more decimal digits, is
matched. The exponent, if present, specifies the power of ten by
which the decimal fraction is multiplied. The argument is assumed
to point to an object of type float.
i
An optional sign, followed by an octal, decimal or hexadecimal
constant is matched. An octal constant consists of "0" and zero or
more octal digits. A decimal constant consists of a non-zero
decimal digit and zero or more decimal digits. A hexadecimal
constant consists of the characters "0x" or "0X" followed by one or
more (upper- or lowercase) hexadecimal digits. The argument is
assumed to point to an object of type int.
n
No input data is processed. Instead, the number of characters that
have already been read is assigned to the object of type unsigned
int that is pointed to by the argument. The number of items that
have been scanned and assigned (the return value) is not affected by
the "n" conversion type specifier.
o
An octal integer, consisting of an optional sign, followed by one or
more (zero or non-zero) octal digits, is matched. The argument is
assumed to point to an object of type int.
p
A hexadecimal integer, as described for "x" conversions below, is
matched. The converted value is further converted to a value of
type void* and then assigned to the object pointed to by the
argument.
s
A sequence of non-white-space characters is matched. The argument
is assumed to point to the first element of a character array of
sufficient size to contain the sequence and a terminating null
character, which is added by the conversion operation.
u
An unsigned decimal integer, consisting of one or more decimal
digits, is matched. The argument is assumed to point to an object
of type unsigned int.
x
A hexadecimal integer, consisting of an optional sign, followed by
an optional prefix "0x" or "0X", followed by one or more (upper- or
lowercase) hexadecimal digits, is matched. The argument is assumed
to point to an object of type int.
[c1c2...]
A sequence of characters, consisting of any of the characters c1,
c2, ... called the scanset, in any order, is matched. c1 cannot be
the caret character (''). If c1 is "]", that character is
considered to be part of the scanset and a second "]" is required to
end the format directive. The argument is assumed to point to the
first element of a character array of sufficient size to contain the
sequence and a terminating null character, which is added by the
conversion operation.
[.2...]
A sequence of characters, consisting of any of the characters other
than the characters between the "" and "]", is matched. As with
the preceding conversion, if c1 is "]", it is considered to be part
of the scanset and a second "]" ends the format directive. The
argument is assumed to point to the first element of a character
array of sufficient size to contain the sequence and a terminating
null character, which is added by the conversion operation.
A conversion type specifier of "%" is treated as a single ordinary
character that matches a single "%" character in the input data. A
conversion type specifier other than those listed above causes scanning
to terminate the function to return.
The line
scanf( "%s%*f%3hx%d", name, &hexnum, &decnum )
with input
some_string 34.555e-3 abc1234
will copy "some_string" into the array name, skip 34.555e-3, assign
0xabc to hexnum and 1234 to decnum. The return value will be 3.
The program
#include <stdio.h>
void main()
{
char string1[80], string2[80];
scanf( "%[abcdefghijklmnopqrstuvwxyz"
"ABCDEFGHIJKLMNOPQRSTUVWZ ]%*2s%[\n]",
string1, string2 );
printf( "%s\n%s\n", string1, string2 );
}
with input
They may look alike, but they don't perform alike.
will assign
"They may look alike"
to string1, skip the comma (the "%*2s" will match only the comma; the
following blank terminates that field), and assign
" but they don't perform alike."
to string2.
Classification:
ANSI, (except for F and N modifiers)
Systems:
All
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