Obtain the length of the start portion that includes the specified character string among the strings
size_t __far strspn(const char __near *s1, const char __near *s2);
size_t __far _COM_strspn_ff(const char __far *s1, const char __far *s2);
Returns the length of the portion that has been found.
This function obtains the maximum and first length of the portion consisting of only the characters (except the null character (\0)) in the character string indicated by s2, in the character string indicated by s1.