Combining Strings - Segmentation Fault - High Level Programming

Octal · #1 02-10-2007

I am writing a function to combine strings, but when I execute I get a segmentation fault, which doesn't make sence. Segmentation fault is when you try to acess a point of memory that doesn't exist, like trying to acess array[10] when you declared array[7].

Here is the source code:

Code:

#include <stdio.h>
/* #include <string.h> == cheating! */

#define MAXINPUT 1000

char combine(char string1[MAXINPUT], char string2[MAXINPUT]) {
	int count1, count2 = 0;

	while (string1[count1] != '\0')
		++count1;

	while (string2[count2] != '\0')
		string1[count1++] = string2[count2++];
	string1[count1] = '\0';
}
main() {
	char string1[MAXINPUT];
	char string2[MAXINPUT];
	int i = 0;
	
	printf("Enter two strings each under 1000 characters:\n");
	while(i = 0) {
		printf("1: ");
		scanf("%s", string1);
		if ((sizeof string1) > MAXINPUT) {
			i = 0;
			printf("I said under 1000 characters, please enter it again:\n");
		}
		else
			i = 1;
	}
	i = 0;
	while(i = 0) {
		printf("\n2: ");
		scanf("%s", string2);
		if ((sizeof string2) > MAXINPUT) {
			i = 0;
			printf("I said under 1000 characters, please enter it again:\n");
		}
		else
			i = 1;
	}
	printf("%s and %s combined is %s", string1, string2, combine(string1, string2));
	return 0;
}

I know there are functions in the string.h header, but as you can see, I wanted to do it without them, thus calling those functions "cheating".

Thanks for reading.

Perderabo · #2 02-10-2007

(sizeof string1) is a constant and will not vary depending on the contents of string1. And what if 1200 characters were entered? Where do you think the extra 200 will be? You seem to be intentionally blowing arrays.

But your problem is the combine routine. It returns a character, not a string. Or it would had you returned *anything*. Then you use this character as a pointer to character. It looks like you might mean for combine to return a pointer to character. If so, define it that way and put in a return statement.

Octal · #3 02-10-2007

Quote:

Originally Posted by Perderabo

But your problem is the combine routine. It returns a character, not a string. Or it would had you returned *anything*. Then you use this character as a pointer to character. It looks like you might mean for combine to return a pointer to character. If so, define it that way and put in a return statement.

I'm sorry, but what does that have to do with the segmentation fault?

milhan · #4 02-10-2007

1.st problem:

Quote:

Originally Posted by Octal

Here is the source code:

Code:

char combine(char string1[MAXINPUT], char string2[MAXINPUT]) {
	int count1, count2 = 0;

	while (string1[count1] != '\0')
		++count1;

	while (string2[count2] != '\0')
		string1[count1++] = string2[count2++];
	string1[count1] = '\0';
}

the function is declared as returning char; however there is no return statement that actually returns a char. In this case the function will return a "garbage" value even if the syntax is not necessarily incorrect!

2.nd problem:

Code:

..
	
	printf("Enter two strings each under 1000 characters:\n");
	while(i = 0) {   // should be while (i == 0)
		printf("1: ");
		scanf("%s", string1);
		if ((sizeof string1) > MAXINPUT) {
			i = 0;
			printf("I said under 1000 characters, please enter it again:\n");
		}
		else
			i = 1;
	}
	i = 0;
	while(i = 0) {   // should be while (i == 0)
		printf("\n2: ");
		scanf("%s", string2);
		if ((sizeof string2) > MAXINPUT) {
			i = 0;
			printf("I said under 1000 characters, please enter it again:\n");
		}
		else
...

Perderabo · #5 02-10-2007

Quote:

Originally Posted by Octal

I'm sorry, but what does that have to do with the segmentation fault?

Umm, it's the cause.

Octal · #6 02-10-2007

Thanks milhan, you explained it better. I still get a segmentation fault that I don't understand, the current source (almost same as before) :

Code:

#include <stdio.h>
/* #include <string.h> == cheating! */

#define MAXINPUT 1000

char combine(char string1[MAXINPUT], char string2[MAXINPUT]) {
	int count1, count2 = 0;

	while (string1[count1] != '\0')
		++count1;

	while (string2[count2] != '\0')
		string1[count1++] = string2[count2++];
	string1[count1] = '\0';
	return string1;
}
main() {
	char string1[MAXINPUT];
	char string2[MAXINPUT];
	int i = 0;
	
	printf("Enter two strings each under 1000 characters:\n");
	while(i == 0) {
		printf("1: ");
		scanf("%s", string1);
		if ((sizeof string1) > MAXINPUT) {
			i = 0;
			printf("I said under 1000 characters, please enter it again:\n");
		}
		else
			i = 1;
	}
	i = 0;
	while(i == 0) {
		printf("2: ");
		scanf("%s", string2);
		if ((sizeof string2) > MAXINPUT) {
			i = 0;
			printf("I said under 1000 characters, please enter it again:\n");
		}
		else
			i = 1;
	}
	printf("%s and %s combined is %s", string1, string2, combine(string1, string2));
	return 0;
}

I get an erorr related to

Code:

return string1;

Which is exactly as put:

Code:

combine-strings.c:15: warning: return makes integer from pointer without a cast

so, I assume that I could redeclare string1 as an int, to make the program compile, even though it wouldn't run correctly, because int is numbers(it can be ascii, but that adds up fast), and char is text. So I declare string1 like:

Code:

return (int) string1;

and I get a segmentaton fault after I enter the two strings. I assume that the int was the problem, so I try a few other examples:

Code:

return string1[0];

Which produces segmentation erorr when executed.

Code:

return string1[MAXLINE];

Also produces segmentation erorr when executed.

The odd part is I don't seem to be asking for a part of memory that doesn't exist.

milhan · #7 02-11-2007

octal look at your combine(char [], char[]) function again. I didn't see it at my previous post either.

Code:

char combine(char string1[MAXINPUT], char string2[MAXINPUT]) {
	int count1, count2 = 0;   // you didn't initialize count1, so=> int count1 = 0, count2 = 0;
                         
	while (string1[count1] != '\0')
		++count1;

	while (string2[count2] != '\0')
		string1[count1++] = string2[count2++];
	string1[count1] = '\0';
	return string1;
}

Quote:

Code:

return string1[0];

Which produces segmentation erorr when executed.

return string1[0] is correct. The segmentation fault can't come from here. Try running again with the correction in the combine func. and return string1[0]..

More UNIX and Linux Forum Topics You Might Find Helpful
Thread	Thread Starter	Forum	Replies	Last Post
Why not a segmentation fault??	lagigliaivan	High Level Programming	22	05-21-2008 08:07 AM
Segmentation fault	big123456	Linux	0	07-20-2007 02:01 AM
Segmentation Fault	compbug	UNIX for Dummies Questions & Answers	3	04-21-2006 07:43 AM
Segmentation fault	jshaulis	AIX	1	06-01-2004 01:16 PM
segmentation fault	omran	High Level Programming	2	08-01-2003 05:19 AM

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode