_CP_substr is equivalent to the result = string[beg.pos.expression, len.expression] BASIC statement.
int _CP_substr(CPSTR** result, CPSTR* string, int beg.pos.expression, int len.expression)
This function returns -1 if an error occurs. The error code is contained in _CP_errno.
/* Prints "h". */ CPSTR * s = _CP_mkstr("hi"); _CP_substr(&s,s,1,1); _CP_print(s);