This section describes the miscellaneous input conversions.
The `%p' conversion is used to read a pointer value. It recognizes the same syntax as is used by the `%p' output conversion for printf (see Other Output Conversions); that is, a hexadecimal number just as the `%x' conversion accepts. The corresponding argument should be of type void ** ; that is, the address of a place to store a pointer.
The resulting pointer value is not guaranteed to be valid if it was not originally written during the same program execution that reads it in.
The `%n' conversion produces the number of characters read so far by this call. The corresponding argument should be of type int * . This conversion works in the same way as the `%n' conversion for printf ; see Other Output Conversions, for an example.
The `%n' conversion is the only mechanism for determining the success of literal matches or conversions with suppressed assignments. If the `%n' follows the locus of a matching failure, then no value is stored for it since scanf returns before processing the `%n'. If you store -1 in that argument slot before calling scanf , the presence of -1 after scanf indicates an error occurred before the `%n' was reached.
Finally, the `%%' conversion matches a literal `%' character in the input stream, without using an argument. This conversion does not permit any flags, field width, or type modifier to be specified.