>>680
ISO/IEC 9899:1999
　if it has pointer type, it is initialized to null pointer;
　if it has arithmetic type, it is initialized to
　　(positive or unsigned) zero;
　if it is an aggregate, every member is initialized
　　(recursively) according to these rules;
　if it is a union, the first named member is initialized
　　(recursively) according to these rules.