Thread: Pointers problem

I have a simple question. Let's say I want to change all the spaces in a given string with a '+' character. I have to do this with pointers.

Code:

 void change(char *ps){
         while((*ps++)!='\0'){
                       if(*ps==' '){
                                  *ps='+';  // this seems to be wrong ...But how do I change the 
                                                 //value that the pointer is pointing to??
                        }
                   }
   }

Yes, you did it right. You dereference what it points to and change it. However, you skip the first character checking for a space. Maybe a do-while loop for kicks. Also, just for fun, '\0' is the same as 0, so you don't need to explicitely check for it. Re-arranged, it might look like:

Code:

	do {
		if(*ps == ' ')
			*ps = '+';
	} while(*ps++);

I still get the segmentation fault

String literals are not necessarily modifiable Ch-ch-ch-check it: http://www.eskimo.com/~scs/C-faq/q6.2.html

Aaaaaaaaaa...thanks man! I was using a char *str instead of char str[]....

Why can't you use char* str instead of char str[] here? As long as you made sure the string was null terminated, there shouldn't be a problem - should there?

If you declare char *str = "foo"; you can't then modify it with str[0]. This is because attempting to modify a string literal yields undefined behaviour. In modern operating systems, a string literal will often be stored in read-only memory, causing a violation when your program attempts to change it. See the FAQ posted above.

Originally Posted by Korg

Why can't you use char* str instead of char str[] here? As long as you made sure the string was null terminated, there shouldn't be a problem - should there?

The char *str is null terminated too, but...see cwr's post above.

Thanks guys for clearing that to me!