Case Sensitivity... matching words in a string.

Hi there,

I am writing a simple scanner for school to better understand compilers. I can't seem to figure out why in the following code the token ElSe still matches when I compare it character by character to capital letters (ELSE). So in the scanner ElSe would be a variable not a keyword as it is not all in caps.

Code:

int iskeyword(char * kw_lexeme){
/*	NOT A KEYWORD = -1 */
/*	"ELSE" = 0 */
/*  "IF"   = 1 */
/*  "INPUT" = 2 */
/*  "OUTPUT" = 3 */
/* "PLATYPUS" = 4 */
/* "REPEAT" = 5 */
/* "THEN" = 6 */
/* "USING" = 7 */

	switch(kw_lexeme[0]){
   	case 'E':
      	if(kw_lexeme[1]=='L' && kw_lexeme[2]=='S' && kw_lexeme[3]=='E'){
            return 0;
         	break;
         }
   	case 'I':
      	if(kw_lexeme[1]=='F')
         	return 1;
         else if(kw_lexeme[1]=='N' && kw_lexeme[2]=='P' && kw_lexeme[3]=='U' && kw_lexeme[4]=='T')
         	return 2;
         break;
   	case 'O':
      	if(kw_lexeme[1]=='U' && kw_lexeme[2]=='T' && kw_lexeme[3]=='P' && kw_lexeme[4]=='U' && kw_lexeme[5]=='T')
         	return 3;
         break;
   	case 'P':
      	if(kw_lexeme[1]=='L' && kw_lexeme[2]=='A' && kw_lexeme[3]=='T' && kw_lexeme[4]=='Y' && kw_lexeme[5]=='P' && kw_lexeme[6]=='U' && kw_lexeme[7]=='S')
         	return 4;
         break;
   	case 'R':
      	if(kw_lexeme[1]=='E' && kw_lexeme[2]=='P' && kw_lexeme[3]=='E' && kw_lexeme[4]=='A' && kw_lexeme[5]=='T')
         	return 5;
         break;
   	case 'T':
      	if(kw_lexeme[1]=='H' && kw_lexeme[2]=='E' && kw_lexeme[3]=='N')
         	return 6;
         break;
   	case 'U':
      	if(kw_lexeme[1]=='S' && kw_lexeme[2]=='I' && kw_lexeme[3]=='N' && kw_lexeme[4]=='G')
         	return 7;
         break;
      default:
      		return -1;
   }


}

So basically why is ElSe returning a 0 when it should be the default -1?

Thanks

kw_lexeme[1]=='L' and not 'l'

Originally Posted by themsaman

kw_lexeme[1]=='L' and not 'l'

Yes I have it as 'L' now because I only want capitals to match.

ELSE\0 as argument should return 0
ElSe\0 SHOULD return -1 but is returning 0.

Uhhh... beats me to be honest. Did you check what is happening with a debugger? Is it going through that branch

ElSe should return lkasjhltiuq3gto4997aguwhfl, and not -1, since no return statement is encountered in the program flow for that input. The exact value of lkasjhltiuq3gto4997aguwhfl is going to vary from machine to machine, of course.

*Note: The bit about lkasjhltiuq3gto4997aguwhfl is not true. But the "no return statement" part is true, meaning the return value could be (and will be) any number at all -- this is why your compiler is telling you "not all control paths return a value" or similar (unless you turned off warnings, which you generally shouldn't do). The default case will not get hit if you go into a specific case and then use break. (Also, you may notice an interesting result if you use "EF" as input as well....)

Originally Posted by braden87

ELSE\0 as argument should return 0
ElSe\0 SHOULD return -1 but is returning 0.

According to your code "ElSe" should return an undefined value, which in this case happens to be 0.
The default case in a switch case only gets executed if no other case match, or if the case before it doesn't have a break statement.
The "not all code paths return a value" warning you should be getting from the compiler is not something that should be ignored

Edit:
Looks like tabstop beat me to it..