int sscanf(const char *s,
           const char *format,

sscanf reads input from the string s under control of the string pointed to by format that specifies the admissible input sequences and how they are to be converted for assignment, using subsequent arguments as pointers to the objects to receive the converted input.

If there are insufficient arguments for the format, the behavior is undefined. If the format is exhausted while arguments remain, the excess arguments are evaluated but are otherwise ignored.

sscanf returns the value of the macro EOF if an input failure occurs before any conversion. Otherwise, sscanf returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure.