Get length of a prefix substring
#include <string.h> size_t strspn(const char *s, const char *accept); size_t strcspn(const char *s, const char *reject);
The strspn() function calculates the length (in bytes) of the initial segment of s which consists entirely of bytes in accept.
The strcspn() function calculates the length of the initial segment of s which consists entirely of bytes not in reject.
The strspn() function returns the number of bytes in the initial segment of s which consist only of bytes from accept.
The strcspn() function returns the number of bytes in the initial segment of s which are not in the string reject.
The strspn() and strcspn() functions are thread-safe.
SVr4, 4.3BSD, C89, C99.
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