CODEWITHSUNDEEP
c++pointersmultidimensional-array
Tyler Hughes
Tyler Hughes

Reputation: 23

Initializing a 2D Array within a function, calling by pointer. Getting Segmentation Fault

The objective of this program is of right now to set each array variable of the 2D array,

char mass_data_shift[9][9]; equal to 'T' . Which should equal 100 Ts overall.

This is done by calling a void function with this 2D array address as an argument. Calling it by a pointer to then be initialized in a loop.

Inside the loop is were the 2D array should be set to T.

*mass_data[mass_data_counter][mass_data_counter_two] = 'T';

However..... the program results in:

Meaning the program, somewhere, is writing out of bounds. Any help would be appreciated in both making the program run without a segmentation fault and/or fixing other mistakes. 

#include <stdlib.h>
#include <stdio.h>
#include <iostream>

void mass_data_define(char (*mass_data)[9][9]){

  int mass_data_counter;
  int mass_data_counter_two = 0;

  for (mass_data_counter=0;mass_data_counter<9;mass_data_counter++){
    do {    
      std::cout << "|Array #1   " << mass_data_counter
                << "   :::   |Array #2    " << mass_data_counter_two 
                << std::endl;

      *mass_data[mass_data_counter][mass_data_counter_two] = 'T';

      std::cout << *mass_data[mass_data_counter][mass_data_counter_two];

      mass_data_counter_two++;
      std::cout << "---------End of Counter 2 Init Code----------" << std::endl;
    } while (mass_data_counter_two < 9);

    mass_data_counter_two = 0;
  }
}

int main()
{
    char mass_data_shift[9][9];

    mass_data_define(&mass_data_shift);

    std::cout << "-END-" << std::endl;

    return 0;
}

Final Edit: The main cause was solved by szym below. Sorry about the whitespaces and missing iostream , was a formatting issue when I made the post. Also changed the loop to fit the array length as suggested below.

Upvotes: 2

Views: 108

Answers (2)

lifebalance
lifebalance

Reputation: 1927

Short Answer: Here's a one-line fix to your code so may continue to use a pointer and still not get a segmentation fault: 

        (*mass_data)[mass_data_counter][mass_data_counter_two] = 'T';

Long Answer: Read Create a pointer to two-dimensional array.

For an in-depth understanding of how to pointers to access multi-dimensional arrays, read this.

Upvotes: 0

szym
szym

Reputation: 5846

*mass_data[mass_data_counter][mass_data_counter_two] = 'T';

Should be

(*mass_data)[mass_data_counter][mass_data_counter_two] = 'T';

Naturally, same goes for the line: 

std::cout << *mass_data[mass_data_counter][mass_data_counter_two]

But really this pointer type is not necessary to pass array by reference in C/C++.

You should instead declare:

void mass_data_define(char mass_data[9][9]) {
    // To read:
    char z = mass_data[3][6];
    // To write:
    mass_data[2][1] = 'C';
}

// elsewhere
char my_mass_data[9][9];
mass_data_define(my_mass_data);

Upvotes: 1

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