Thread: why do i get segmentation fault here?and how do i fix it?

  1. #1
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    why do i get segmentation fault here?and how do i fix it?

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <time.h>
    
    
    int printboard( int **board,int N);
        
    int main()
    {
        int i,j;
        int N=5;
      
        
        int board[N][N];
      
        
        for(i=0;i<N;i++){
            for(j=0;j<N;j++){
                board[i][j]=1;
            }
        }
        
            
        printboard( board,N);   
        return 0;
    }
    
    
    
    
    int printboard( int **board,int N){
        int i,j;
        for(i=0;i<N;i++){
            for(j=0;j<N;j++){
                printf("%d",board[i][j]);
            }
        }
    }
    Attached Images Attached Images why do i get segmentation fault here?and how do i fix it?-jpg 

  2. #2
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    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <time.h>
     
    #define SIZE 5
     
    void printboard(int board[][SIZE]);
     
    int main() {
        int board[SIZE][SIZE];
     
        for (int i = 0; i < SIZE; i++)
            for (int j = 0; j < SIZE; j++)
                board[i][j] = 1;
     
        printboard(board);
     
        return 0;
    }
     
    void printboard(int board[][SIZE]) {
        for (int i = 0; i < SIZE; i++) {
            for (int j = 0; j < SIZE; j++)
                printf("%2d ", board[i][j]);
            putchar('\n');
        }
    }
    If you want the truth to stand clear before you, never be for or against. - Sent-ts'an

  3. #3
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    thing is i need to get the size from the console with argv.i just simplified the problem so you can send me an easy fix

  4. #4
    C++ Witch laserlight's Avatar
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    The issue you have is that when an array is passed as an argument, it is converted to a pointer to its first element. This means that an array of arrays is converted to a pointer to an array, not a pointer to a pointer. This is why john.c's example retains the SIZE in the parameter.

    Note that your array of arrays is actually a variable length array, whereas you probably want a fixed size array as shown by john.c.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  5. #5
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    If you really want to use a variable-size array, then maybe something like this.
    I also randomized the values.
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <time.h>
     
    void printboard(int Size, int board[][Size]) {
        for (int i = 0; i < Size; i++) {
            for (int j = 0; j < Size; j++)
                printf("%2d ", board[i][j]);
            putchar('\n');
        }
    }
     
    int main(int argc, char **argv) {
        int Size = 5;
     
        if (argc > 2) {
            fprintf(stderr, "Usage: board [SIZE]\n");
            return EXIT_FAILURE;
        } 
     
        if (argc == 2) Size = atoi(argv[1]);
     
        if (Size <= 0) {
            fprintf(stderr, "The size must be > 0\n");
            return EXIT_FAILURE;
        }
     
        int board[Size][Size];
       
        for (int i = 0; i < Size; i++)
            for (int j = 0; j < Size; j++)
                board[i][j] = rand() % 2;
         
        printboard(Size, board);
     
        return 0;
    }
    Last edited by john.c; 01-28-2020 at 03:12 PM.
    If you want the truth to stand clear before you, never be for or against. - Sent-ts'an

  6. #6
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    Quote Originally Posted by laserlight View Post
    Note that your array of arrays is actually a variable length array, whereas you probably want a fixed size array as shown by john.c.
    Interesting. I didn't know this!
    I prefer to deal with multidimensional arrays as an argument through a single pointer:
    Code:
    void f(int size, int *ptr)
    {
      int i, j, *p;
      for ( i = 0; i < size; i++ )
        for ( j = 0; j < size; j++ )
        {
          p = ptr + size * j + i; // p points to "ptr[i][j]".
          ...
        }
    }

  7. #7
    and the hat of int overfl Salem's Avatar
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    > why do i get segmentation fault here?and how do i fix it?
    You read the error message and fix the code, before trying to run it.

    That warning that was printed in your screen shot wasn't a slap on the wrist, it was a gun at your head.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

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