C / C++ / MFC

const int uc='a'-'A';
bool bMatch=c==d || c+uc==d && c>='A' && c<='Z' || c==d+uc && d>='A' && d<='Z';

//case insensitive search functions...
#ifdef UNICODE
#define _tcsustr wcsustr
#else
#define _tcsustr strustr
#endif
char* strustr(char *source, char *s);
wchar_t* wcsustr(wchar_t *source, wchar_t *s);

char* strustr(char *source, char *s)
{
	//make an uppercase copy af source and s
	char *csource = strdup(source);
	char *cs = strdup(s);
	strupr(csource);
	strupr(cs);
	//find cs in csource...
	char *result = strstr(csource, cs);
	if (result != NULL)
	{
		//cs is somewhere in csource
		int pos = result - csource;
		result = source;
		result += pos;
	}
	//clean up
	free(csource);
	free(cs);
	return result;
}

wchar_t* wcsustr(wchar_t *source, wchar_t *s)
{
	//make an uppercase copy af source and s
	wchar_t *csource = wcsdup(source);
	wchar_t *cs = wcsdup(s);
	wcsupr(csource);
	wcsupr(cs);
	//find cs in csource...
	wchar_t *result = wcsstr(csource, cs);
	if (result != NULL)
	{
		//cs is somewhere in csource
		int pos = result - csource;
		result = source;
		result += pos;
	}
	//clean up
	free(csource);
	free(cs);
	return result;
}

char * stristr (const char * string , const char * strCharSet )
{
    char *pstart = (char *) string ;
    char *s1, *s2;      
    
    if ( !*strCharSet  )
        return((char *)string );
    
    while (*pstart)
    {
        s1 = pstart;
        s2 = (char *) strCharSet ;
        
        char c1, c2;
        
        while ( *s1 && *s2  )
        {
            c1 = *s1;
            c2 = *s2;
            
            if( __isascii(c1)  && isupper(c1) )
                c1 = islower(c1);
            
            if( __isascii(c2)  && isupper(c2) )
                c2 = islower(c2);
            
            if(c1 - c2)
                break;
            
            s1++;
            s2++;                       
            
        }
        
        
        if (!*s2)
            return(pstart);
        
        pstart++;
    }
    
    return(NULL);
}