The scanf() family of functions shall behave as described in POSIX 1003.1-2008 (ISO/IEC 9945-2009), except as noted below.
%[ conversion specifiers shall accept an
option length modifier
which shall cause a memory buffer to be allocated to hold the string converted.
In such a case, the argument corresponding to the conversion specifier should be
a reference to a pointer value that will receive a pointer to the allocated
buffer. If there is insufficient memory to allocate a buffer, the
function may set
errno to ENOMEM and a
conversion error results.
Note: This directly conflicts with the ISO C (1999) usage of %a as a conversion specifier for hexadecimal float values. While this conversion specifier should be supported, a format specifier such as "%aseconds" will have a different meaning on an LSB conforming system.