Comparing strings without regard to case

I couldn't find a C++/STL built-in comparison function for strings without regard to case. I really thought there would be one, but apparently not.

So here's one for example.

// Compare two strings without regard to alphabetic case 
int stricmp(const char *a, const char *b) { 

 static const int offset = 'a' - 'A';
 for (; *a && *b; a++,b++) { 
  if (*a != *b) { 
   char la = 'A' <= *a && *a <= 'Z' ? *a+offset : *a;   
   char lb = 'A' <= *b && *b <= 'Z' ? *b+offset : *b;   
   int diff = la - lb;
   if (diff) { return diff; }
  }
 }

 return *a ? 1 : *b ? -1 : 0; 

}

// Compare two pointers-to-strings without regard to alphabetic case 
int sorting_stricmp( const void *a, const void *b ) { 
 const char **s1 = (const char **)a;
 const char **s2 = (const char **)b;
 return stricmp(*s1,*s2);
}

// Compare two C++ strings without regard to alphabetic case
int string_icmp(const string &s1, const string &s2) { 
 return stricmp(s1.c_str(), s2.c_str());
}