Thread: pointer - segmentation fault

Hello

This function lookAround searches for the nearest enemy. When it has found this enemy i want to "return" this enemy with a pointer. When I want to write this enemy in the main I get a segmentation fault.

Does anyone has an idea?

Code:

#include <stdio.h>
#include <stdlib.h>
/*#include "Simulation.h"*/
#include "_fgets.h"

void lookAround(int yCoordinate, int xCoordinate, int height, int width, char array[6][6], int radius, char enemy, char *closestEnemy);
int main (void)
{
/*	printf("You’re a desperate man, Sean. Desperate men don’t come to talk. They come to kill\n");*/
	char array[6][6];
	int i, j;
	char *closestEnemy;
	for (i = 0; i < 6; i++){
		for (j = 0; j < 6; j++)
			array[i][j] = 'b';
	}

	array[2][4] = 'a';

	lookAround(2, 2, 6, 6, array, 2, 'a', closestEnemy);
	

	printf("%i\n", *closestEnemy);
	return 0;
}
	
/* This function looks in the world and returns the closest enemy */
void lookAround(int yCoordinate, int xCoordinate, int height, int width, char array[6][6], int radius, char enemy, char *closestEnemy)
{
	int i, j, k, beginY, beginX, endY, endX;
	boolean isTrue = FALSE;

	for (k = 1; k <= radius; k++)
	{
		
		if ((yCoordinate - k) > 0)
			beginY = yCoordinate - k;
		else
			beginY = 0;

		if ((yCoordinate + k) < height)
			endY = yCoordinate + k + 1;
		else
			endY = height;

		if ((xCoordinate - k) > 0)
			beginX = xCoordinate - k;
		else 
			beginX = 0;

		if ((xCoordinate + k) < width)
			endX = xCoordinate + k + 1;
		else
			endX = width;

		for (i = beginX; i < endX && isTrue == FALSE; i++)
		{
			for (j = beginY; j < endY && isTrue == FALSE; j++)
			{
				if (array[i][j] == enemy )
				{
					printf("%c\n", array[i][j]);
					closestEnemy = &array[i][j];
					isTrue = TRUE;
				}
			}
		}
	}
}

In the function lookAround, closestEnemy is a local variable. If you set it to point to something, the change will only remain as long as you're still within the function. If you actually want to change what it points to, you need to pass it like this:

Code:

char **closestEnemy

thanx for your help
I changed my code :
Now i get an warning : assignment from incompatible pointer type
But I dont understand wy

Code:

#include <stdio.h>
#include <stdlib.h>
/*#include "Simulation.h"*/
#include "_fgets.h"

void lookAround(int yCoordinate, int xCoordinate, int height, int width, char array[6][6], int radius, char enemy, char **closestEnemy);
int main (void)
{
/*	printf("You’re a desperate man, Sean. Desperate men don’t come to talk. They come to kill\n");*/
	char array[6][6];
	int i, j;
	char **closestEnemy;
	for (i = 0; i < 6; i++){
		for (j = 0; j < 6; j++)
			array[i][j] = 'b';
	}

	array[2][4] = 'a';

	lookAround(2, 2, 6, 6, array, 2, 'a', closestEnemy);
	

	printf("%c\n", **closestEnemy);
	return 0;
}

/* This function looks in the world and returns the closest enemy */
void lookAround(int yCoordinate, int xCoordinate, int height, int width, char array[6][6], int radius, char enemy, char **closestEnemy)
{
	int i, j, k, beginY, beginX, endY, endX;
	boolean isTrue = FALSE;

	for (k = 1; k <= radius; k++)
	{
		
		if ((yCoordinate - k) > 0)
			beginY = yCoordinate - k;
		else
			beginY = 0;

		if ((yCoordinate + k) < height)
			endY = yCoordinate + k + 1;
		else
			endY = height;

		if ((xCoordinate - k) > 0)
			beginX = xCoordinate - k;
		else 
			beginX = 0;

		if ((xCoordinate + k) < width)
			endX = xCoordinate + k + 1;
		else
			endX = width;

		for (i = beginX; i < endX && isTrue == FALSE; i++)
		{
			for (j = beginY; j < endY && isTrue == FALSE; j++)
			{
				if (array[i][j] == enemy )
				{
					printf("%c\n", array[i][j]);
					closestEnemy = &array[i][j];
					isTrue = TRUE;
				}
			}
		}
	}
}

Ok i changed my code but I still have a segmentation fault.
Did I interprete your advise wrong? Because I can print the value of the double pointer in the function but when i try to print it in the main I get a segmentation fault

Code:

#include <stdio.h>
#include <stdlib.h>
/*#include "Simulation.h"*/
#include "_fgets.h"

void lookAround(int yCoordinate, int xCoordinate, int height, int width, char array[6][6], int radius, char enemy, char **closestEnemy);
int main (void)
{
/*	printf("You’re a desperate man, Sean. Desperate men don’t come to talk. They come to kill\n");*/
	char array[6][6];
	int i, j;
	char **closestEnemy;
	for (i = 0; i < 6; i++){
		for (j = 0; j < 6; j++)
			array[i][j] = 'b';
	}

	array[2][4] = 'a';

	lookAround(2, 2, 6, 6, array, 2, 'a', closestEnemy);
	

	printf("%c\n", **closestEnemy);
	return 0;
}
	
/* This function looks in the world and returns the closest enemy */
void lookAround(int yCoordinate, int xCoordinate, int height, int width, char array[6][6], int radius, char enemy, char **closestEnemy)
{
	int i, j, k, beginY, beginX, endY, endX;
	boolean isTrue = FALSE;
	char *pclosestEnemy;
	for (k = 1; k <= radius; k++)
	{
		
		if ((yCoordinate - k) > 0)
			beginY = yCoordinate - k;
		else
			beginY = 0;

		if ((yCoordinate + k) < height)
			endY = yCoordinate + k + 1;
		else
			endY = height;

		if ((xCoordinate - k) > 0)
			beginX = xCoordinate - k;
		else 
			beginX = 0;

		if ((xCoordinate + k) < width)
			endX = xCoordinate + k + 1;
		else
			endX = width;

		for (i = beginX; i < endX && isTrue == FALSE; i++)
		{
			for (j = beginY; j < endY && isTrue == FALSE; j++)
			{
				if (array[i][j] == enemy )
				{
					pclosestEnemy = &array[i][j];
					closestEnemy = &pclosestEnemy;
					printf("%c\n", **closestEnemy);

					isTrue = TRUE;
				}
			}
		}
	}
}

Thanx it works

that example helped me a lot.