Declarations:
int fscanf(FILE *stream,
const char *format, ...);
int scanf(const char *format,
...);
int sscanf(const char *str, const
char *format, ...);
The ..scanf functions provide a means to input formatted
information from a stream.
fscanf |
reads formatted input from a stream |
scanf |
reads formatted input from stdin |
sscanf |
reads formatted input from a string |
These functions take input in a manner that is specified by
the format argument and store each input field into the
following arguments in a left to right fashion.
Each input field is specified in the format string with a
conversion specifier which specifies how the input is to be
stored in the appropriate variable. Other characters in the
format string specify characters that must be matched from the
input, but are not stored in any of the following arguments. If
the input does not match then the function stops scanning and
returns. A whitespace character may match with any whitespace
character (space, tab, carriage return, new line, vertical tab,
or formfeed) or the next incompatible character.
An input field is specified with a conversion specifer which
begins with the % character. After the
% character come the following in this order:
| [*] |
Assignment suppressor (optional). |
| [width] |
Defines the maximum number of characters to read
(optional). |
| [modifier] |
Overrides the size (type) of the argument
(optional). |
| [type] |
The type of conversion to be applied (required). |
Assignment suppressor:
Causes the input field to be scanned but not stored in a
variable.
Width:
The maximum width of the field is specified here with a decimal
value. If the input is smaller than the width specifier (i.e. it
reaches a nonconvertible character), then what was read thus far
is converted and stored in the variable.
Modifier:
A modifier changes the way a conversion specifier type is
interpreted.
| [modifier] |
[type] |
Effect |
|
h |
d, i,
o, u, x
|
The argument is a short int or
unsigned short int.< /td> |
h |
n |
Specifies that the pointer points to a
short int. |
l |
d, i,
o, u, x
|
The argument is a long int or
unsigned long int . |
l |
n |
Specifies that the pointer points to a long
int. |
l |
e, f,
g |
The argument is a double. |
L |
e, f,
g |
The argument is a long double. |
Conversion specifier type:
The conversion specifier specifies what type the argument is. It
also controls what a valid convertible character is (what kind
of characters it can read so it can convert to something
compatible).
| [type] |
Input |
d |
Type signed int represented in
base 10. Digits 0 through 9 and the sign (+ or -). |
i |
Type signed int. The base
(radix) is dependent on the first two characters. If the
first character is a digit from 1 to 9, then it is base
10. If the first digit is a zero and the second digit is
a digit from 1 to 7, then it is base 8 (octal). If the
first digit is a zero and the second character is an x
or X, then it is base 16 (hexadecimal). |
o |
Type unsigned int. The input
must be in base 8 (octal). Digits 0 through 7 only. |
u |
Type unsigned int. The input
must be in base 10 (decimal). Digits 0 through 9 only. |
x, X |
Type unsigned int. The input
must be in base 16 (hexadecimal). Digits 0 through 9 or
A through Z or a through z. The characters 0x or 0X may
be optionally prefixed to the value. |
e, E,
f, g, G |
Type float. Begins with an
optional sign. Then one or more digits, followed by an
optional decimal-point and decimal value. Finally ended
with an optional signed exponent value designated with
an e or E. |
s |
Type character array. Inputs a sequence of non-whitespace
characters (space, tab, carriage return, new line,
vertical tab, or formfeed). The array must be large
enough to hold the sequence plus a null character
appended to the end. |
[...] |
Type character array. Allows a search set of
characters. Allows input of only those character
encapsulated in the brackets (the scanset). If the first
character is a carrot (^), then the scanset is inverted
and allows any ASCII character except those specified
between the brackets. On some systems a range can be
specified with the dash character (-). By specifying the
beginning character, a dash, and an ending character a
range of characters can be included in the scanset. A
null character is appended to the end of the array. |
c |
Type character array. Inputs the number of
characters specified in the width field. If no width
field is specified, then 1 is assumed. No null character
is appended to the array. |
p |
Pointer to a pointer. Inputs a memory address in the
same fashion of the %p type produced
by the printf function. |
n |
The argument must be a pointer to an int.
Stores the number of characters read thus far in the
int. No characters are read from the
input stream. |
% |
Requires a matching % sign from
the input. |
Reading an input field (designated with a conversion
specifier) ends when an incompatible character is met, or the
width field is satisfied.
On success the number of input fields converted and stored
are returned. If an input failure occurred, then EOF is
returned. |
