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Like printf(), scanf() expects its first argument to be a format string, but unlike printf(), the remaining arguments are addresses of the variables in which to put the data that is read. The prototype for scanf(), also in stdio.h, is:
int scanf(char *, ...);As we've said, the returned value is the number of items read, or EOF. The format string controls the input order, conversion of the input data to the specified type, and format specification. Each conversion specification appearing in the format string is applied, in turn, to the next input data item in the input stream. After the specified conversion, the item is placed where the next succeeding argument points; so each of the arguments must be an address.
Besides the conversion specifications that start with %, the format string may also include regular characters. Regular white space characters in the format string are ignored. Any regular non-white space characters must be matched exactly in the input stream. For example:
scanf("x= %d", &x);
The input stream must include
the characters x=, which are matched by the corresponding character in
the format string, before an integer value is
read. A valid sample input for this format string is:
As before,
a conversion specification starts with a %
and ends with one of the conversion
characters given in Table 8.2.
Between % and the conversion character,
there can be an
optional assignment suppression character, *,
followed by an optional number
indicating the maximum field width. The maximum field width specifies
that no more than that number of characters in the input stream may be used for
the next data item. The converted result is stored where the corresponding
argument points unless the assignment suppression character is used. If the
suppression character is used, the result is discarded.
The conversion characters with their meanings are given
in Table 8.2.
All of these except c and s may be preceded by the length modifier, l (ell), where, in the case of integral type data, the corresponding argument should be long and in the case of floating point data, the argument should be double. For example, with the following declarations:
int i, k;
char c;
float f1;
double d1;
char s[80];
long x;
Consider the following statements with the input as shown below each statement.
scanf("Integer: %4d %f", &i, &f1);
Input is:
scanf("%4s %*c %c", s, &c);
scanf("%s %*s %d", s, &i);