Bug#1059873: 12.14.5 String Input Conversions: The meaning of ‘%[\0a]’ conversion is unclear

[Krzysztof Żelechowski]

It is not clear whether the format string "%[\0a]" matches the input 
string "a" or not.  I interpret the documentation as saying that once 
the selector "%[ " has been opened, the format interpreter must find a 
matching "]", therefore it must not interpret the embedded "\0" as the 
end of the format string. However, trying to use such a format string 
causes the compiler to report the warning "format contains NUL", which 
suggests that using such a format string involves undefined behaviour.