Thread: Program hangs when encounters switch

Hi folks,

I've come across a peculiar behavior of the program written below:

Code:

#include<stdio.h>
#include<stdlib.h>

void removevowels(char* sen);

int main()
{
	char *sen = "Hello, Good Morning!!";
	printf("String before function call: %s\n", sen);
	removevowels(sen);
	printf("String after function call: %s\n", sen);

	return 0;
}

void removevowels(char* sen)
{
	char *p, *q;
	p = q = sen;
	while(*p != '\0'){
		printf("sen = %x\n", sen);
		printf("p = %x\n", p);
		printf("q = %x\n", q);
		printf("%s\n\n", p);

		switch(*p){
			case 'a': case 'e': case 'i': case 'o': case 'u':
			case 'A': case 'E': case 'I': case 'O': case 'U':
				p++;
				break;

			default:
				*q = *p;
				p++;
				q++;
				break;
		}

	}
	*q = '\0';
}

Upon compiling this program using MinGW (on Win XP), the compilation goes fine without errors but the program hangs when it is run.

The same is not happening if I compile and run using Borland C Compiler (on Win XP).

I added a few printf statements and found that it hangs at the switch statement.

Please share your thoughts on this.

Regards
maverix

If by "hangs" you means "throws a segmentation fault", then yes. (At least that's what I got compiling with MinGW on XP.) sen points to a string literal and cannot be modified. And so when you set q to sen, you can't modify q either, since q now points to a string literal. Declare sen as a char array, then strcpy your string literal in there.

Ah!! yes.
I didn't think on those lines.

I changed the declaration as below

Code:

char sen[] = "Hello, Good Morning!!";

and it ran fine... :-)

Thanks for your inputs...

regards
maverix

Originally Posted by Elysia

Yes, I get a segmentation fault as well, but other than that, I'm not sure what the function is supposed to be doing?

I was just writing a function to remove vowels from a string!!!

However, as I had mentioned earlier, the program in the first post works when compiled with Borland C compiler. Any specific reason for it to work. Was wondering why it (BCC) is letting to change a string literal.

regards
maverix