scanf template string is a string that contains ordinary
multibyte characters interspersed with conversion specifications that
start with ‘%’.
Any whitespace character (as defined by the
see Classification of Characters) in the template causes any number
of whitespace characters in the input stream to be read and discarded.
The whitespace characters that are matched need not be exactly the same
whitespace characters that appear in the template string. For example,
write ‘ , ’ in the template to recognize a comma with optional
whitespace before and after.
Other characters in the template string that are not part of conversion specifications must match characters in the input stream exactly; if this is not the case, a matching failure occurs.
The conversion specifications in a
scanf template string
have the general form:
% flags width type conversion
In more detail, an input conversion specification consists of an initial ‘%’ character followed in sequence by:
scanf finds a conversion
specification that uses this flag, it reads input as directed by the
rest of the conversion specification, but it discards this input, does
not use a pointer argument, and does not increment the count of
rather than a pointer to an
The exact options that are permitted and how they are interpreted vary between the different conversion specifiers. See the descriptions of the individual conversions for information about the particular options that they allow.
With the ‘-Wformat’ option, the GNU C compiler checks calls to
scanf and related functions. It examines the format string and
verifies that the correct number and types of arguments are supplied.
There is also a GNU C syntax to tell the compiler that a function you
write uses a
scanf-style format string.
See Declaring Attributes of Functions in Using GNU CC, for more information.