Thread: Bus Error Appending Char to String (char array)

Hello,
I am trying to append a space ' ', onto the end of a char array.
In my main function I must pass a string to another function.
eg) passingFunction("sentence...");
Appending a space must not be done in the main function.
However I am encountering a bus error problem.

Here is code that generates the error:

Code:

#include <stdio.h>
#include <string.h>


void printString(char *);
void passingFunction(char *);


int main()
{
	passingFunction("I hate wonder bread.");
}


void passingFunction(char line[])
{
	int length = strlen(line);
	line[length] = ' ';
	line[length+1] = '\0';
	printString(line);
}


void printString(char line[])
{
	int counter = 0;
	char ch = line[counter];
	while (ch != '\0')
	{
		printf("%c|", ch);
		counter++;
		ch = line[counter];
	}
	printf("\n");
}

I noticed that I do not encounter this problem if I did this:

Code:

#include <stdio.h>
#include <string.h>


void printString(char *);
void passingFunction(char *);


int main()
{
        char line[] = "I hate wonder brea.");
	passingFunction(line);
        printString(line)
}


void passingFunction(char line[])
{
	int length = strlen(line);
	line[length] = ' ';
	line[length+1] = '\0';
	printString(line);
}


void printString(char line[])
{
	int counter = 0;
	char ch = line[counter];
	while (ch != '\0')
	{
		printf("%c|", ch);
		counter++;
		ch = line[counter];
	}
	printf("\n");
}

What is causing this bus error and what would be a possible solution without declaring the array like I did in the second method I have?

The first program passes a string literal to your function, and then tries to modify it, which is a no-no.

The second program succeeds since you're passing a (modifiable) array.

... what would be a possible solution without declaring the array like I did in the second method I have?

The array is actually the best possible choice in this case.

You could allocate memory to a pointer instead, but you'd still be declaring a variable.
You could copy the string to an allocated pointer within the function, and return the pointer, but then you'd have to free that pointer afterwards.

Why do you want to avoid declaring an array?

That's odd, I ran it and it worked.
Is the worry that this is dangerous or not the proper way?

Thx for the explanation.
What I did was this:
char line[1000];
strcpy(line, "I hate wonder bread.");

Is this ok, or am I still trying to access outside the arrays bounds?

Originally Posted by laserlight

In practice, string literals are not necessarily stored in a place in memory such that they can be modified. Hence, the C standard states that attempting to modify a string literal results in undefined behaviour. This means that it could appear to work, or it might result in something strange, or in an error such as the one that you observed.


Accessing an array out of bounds, e.g., by writing beyond its bounds, also results in undefined behaviour. You can sometimes get away with writing just a little beyond the end of an array because the allocation of memory may have alignment requirements, or you might be overwriting memory for a variable that you do not access afterwards and hence it looks like nothing went wrong.

Understood.
Honestly my problem is bigger than the question asked. I just quickly made a simplified program to show the problem I was having so I didn't pay much attention to names etc.
However I didn't know I could use names in prototypes, thanks.