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12.14.7 Other Input Conversions

This section describes the miscellaneous input conversions.

The `%p' conversion is used to read a pointer value. It recognizes the same syntax 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.