2.2.34 size_t strspn
size_t strspn(const char *__s, const char *__accept) __ATTR_PURE__
The strspn() function calculates the length of the initial segment of s
which consists entirely of characters in accept
.
Remember:
The strspn() function returns the number of characters in the initial segment of s
which consist only of characters from accept
. The terminating zero is not considered as a part of string.