/sys$common/syshlp/helplib.hlb CC, Run-time functions, strspn  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Searches a string for the occurrence of a character that is not in
  a specified set of characters.

  Syntax:

       #include <string.h>

       size_t strspn(const char *str, const char *charset);