char (*pfnStringSearch)(const char *, const char *);
    ...
    pfnStringSearch = ((iCaseSensitive)?strcasestr:strstr);

produces

    warning: assignment from incompatible pointer type
    error: invalid type argument of ‘unary *’

The two subroutines are defined as

    char *strstr(const char *haystack, const char *needle);
    char *strcasestr(const char *haystack, const char *needle);