Thread: segmentation violation??

Hi, I'm on excersise 5-6 in The C Programming Language book and while making the itoa function program encountered a seg fault...

Code:

/* itoa.c */
/* second version of itoa
* this time using pointers
* instead of array indexing
*/

/* includes */
#include <stdlib.h>
#include <stdio.h>
#include <windows.h>

/* function prototypes */
int batoi(char *s);
char *bitoa(int n);
void reverse(char *s);
int bstrlen(char *s);

int main(int argc, char **argv)
{
	if (argc != 2) {         /* print usage and exit */
		fprintf(stderr, "Usage: %s <num>\n", argv[0]);
		return EXIT_FAILURE;
	}
	char *string = argv[1];
	printf("\n\nConverting string to integer...\n\n");
	sleep(5);
	int integer = batoi(string);
	printf("Just to clarify here is the number (+1 to prove its a number): %d\n", integer + 1);
	sleep(5);
	printf("\n\nConverting back to string format...\n\n");
	sleep(5);
	string = bitoa(integer);
	printf("And here's the resulting string: %s\n", string);
	return EXIT_SUCCESS;
}

int batoi(char *s)
{	
	int num, sign;
	sign = (*s == '-') ? -1 : 1;
	for (num = 0; *s != '\0'; s++)            /* get number */
		num = 10 * num + (*s - '0');
	return num * sign;
}

char *bitoa(int n)
{
	int sign = n;
	char *buffer, *ptr;          /* used for the resulting string */
	ptr = buffer;
	if (n < 0)
		n = -n;                  /* make positive for manipulation */
	do {
		*buffer = n % 10 + '0';                  /* get digit */
		++buffer;
	} while (n /= 10);
	if (sign < 0) {             /* if original number was negative then add the '-' symbol to the string */
		*buffer = '-';
		++buffer;
	}
	*buffer = '\0';
	reverse(buffer);
	return ptr;
}

void reverse(char *s)
{
	int temp;
	int count_s, count_t;
	char *t = s;
	for (*t += bstrlen(s), count_s = 0, count_t = bstrlen(s); count_s < count_t; ++s, ++count_s, --t, --count_t) {          /* reverse the string, swapping each char on opposite sides until s and t meet halfway */
		temp = *s;
		*s = *t;
		*t = temp;
	}
}

int bstrlen(char *s)
{
	int num = 0;
	while (*s) {      /* count chars */
		++num;
		++s;
	}
	return num;
}

I'm sure its the bitoa function and I've tried allsorts to solve the problem.
I got rid of the seg fault by just returning a pointer to a normal string like this...

Code:

char *bitoa(int n)
{
	char buffer[] = "hello world";
	char *ptr = buffer;
	return ptr;
}

but that results in printing random binary chars, I don't know what else to try??

Most compilers will give you an error message that conatains a line number in your source code...
Post your errors and, if possible, mark the line that's giving you the error...

In bitoa() you are not allocating memory for your string. A pointer is not a string.

For your smaller code segment, you need to know that C cannot return an array or a pointer to the array. The char array you created in your function is destroyed as the function exits. If you want to return a pointer to a string you need to use malloc() to allocate space for it and then you will need to free() that memory when you are done with it.

In the following snippet:

Code:

char *bitoa(int n)
{
	char buffer[] = "hello world";
	char *ptr = buffer;
	return ptr;
}

You are trying to return an address to a local variable. When the function returns to the calling function this local variable is no longer valid.

Jim

ok, thanks i will try malloc() and free()

Instead of returning a pointer I have just added a string as an extra parameter to the bitoa() function.
Thanks for the help.