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; } } } } }

Because closestEnemy is now a pointer to a pointer, when assigning a value to it in the lookAround function you need to dereference it first..(*clostestEnemy) = whateverValue..

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; } } } } }

closestEnemy should not be ** in main(). Here's an example of how this works:

Code:

#include <stdio.h> void testfunc (int **ptp, int ray[3]) { *ptp = &ray[1]; } int main() { int ray[3] = { 1, 2, 3 }, *ptr; testfunc(&ptr, ray); printf("%d\n",*ptr); return 0; }

You are submitting the address of the ptr (&), which is the same thing as a "pointer to a pointer". When that is dereferenced (*) in testfunc to yield a value, that value is the address pointed to by ptr -- which you can reassign that (eg, to the address of ray[1]).

Thanx it works

that example helped me a lot.