Programming in C

Formatted I/O: printf and scanf
355
The final set of output shows the use of the %n format characters. In this case, the
corresponding argument to printf must be of type pointer to int, unless a type modifier
of hh, h, l, ll, j, z, or t is specified. printf actually stores the number of characters it
has written so far into the integer pointed to by this argument. So, the first occurrence
of %n causes printf to store the value 4 inside the integer variable c1 because that’s how
many characters have been written so far by this call.The second occurrence of %n causes
the value 12 to be stored inside c2. This is because 12 characters had been displayed at
that point by printf. Notice that inclusion of the %n inside the format string has no
effect on the actual output produced by printf.
The scanf Function
Like the printf function, many more formatting options can be specified inside the format
string of a scanf call than have been illustrated up to this point. As with printf,
scanf takes optional modifiers between the % and the conversion character.These
optional modifiers are summarized in Table 16.5.The possible conversion characters that
can be specified are summarized in Table 16.6.
When the scanf function searches the input stream for a value to be read, it always
bypasses any leading so-called whitespace characters, where whitespace refers to either a
blank space, horizontal tab ('\t'), vertical tab ('\v'), carriage return ('\r'), newline
('\n'), or form-feed character ('\f').The exceptions are in the case of the %c format
characters—in which case, the next character from the input, no matter what it is, is
read—and in the case of the bracketed character string—in which case, the characters
contained in the brackets (or not contained in the brackets) specify the permissible characters
of the string.
Table 16.5 scanf Conversion Modifiers
Modifier Meaning
* Field is to be skipped and not assigned
size
Maximum size of the input field
hh
Value is to be stored in a signed or unsigned char
h
Value is to be stored in a short int
l
Value is to be stored in a long int, double, or wchar_t
j, z, or t Value is to be stored in a size_t (%j), ptrdiff_t (%z), intmax_t,or
uintmax_t (%t)
ll
Value is to be stored in a long long int
L
Value is to be stored in a long double
type
Conversion character