Segmentation Fault (core dumped) when allocating memory for 2D array

Question

I'm trying to read specific chars inside a file redirected from stdin into a 2D array, I'm not sure if I'm allocating the memory for the 2D array properly. The first line inside the file is the dimensions of the matrix I'm trying to copy.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "QueueImplementation.c"

int tester(char *s, int cnt)
{
        int num1, num2;
        if(cnt == 0)
        {
                sscanf(s, "%d %d", &num1, &num2);
                if(num1 < 2 || num1 > 20 || num2 < 2 || num2> 20)
                {
                        printf("Incorrect Matrix Dimensions!");
                        printf("\n");
                }
                return num1;
        }
}

void allocateMem(char ***cell, int n, int m)
{
        *cell=(char**)malloc(n*sizeof(int*));
        for(int i=0;i<n;i++)
                *cell[i]=(char*)malloc(m*sizeof(int));
}
int main(){
        char buffer[200];
        int j,max_row,max_col;
        int count = 0;
        int i = 0;
        while (fgets(buffer, sizeof buffer, stdin))
        {
                if(count == 0)
                        max_col = tester(buffer, count);
        count++;
        }
        max_row = count - 1;
        char** cell;
        allocateMem(&cell, max_row, max_col);
        while (fgets(buffer, sizeof buffer, stdin))
        {
                for(j = 0;j<max_col;j++)
                {
                        if(buffer[j] != '\n' && buffer[j] != ' ' && buffer[j] < '0')
                                cell[i-1][j] = (char) buffer[j];
                }
                i++;
        }
        for (i = 0;i<max_row;i++)
        {
                for (j = 0;j<max_col;j++)
                {
                        printf("%c", cell[i][j]);
                }
        }
}

Test file that I redirect consists of

12 10
oooooooooooo
ooooooooooo.
oooooooo....
se.......ooo
oooooooo....

Mainly consists of "o" and "." except for a single "s" and "e". The 12 and 10 are the dimensions of the matrix that I am trying to copy, so the expected output should be the matrix consisting the o's and .'s along with a single "s" and "e".

`*cell[i]=(char*)malloc(m*sizeof(int));` --> `(*cell)[i]=malloc(m*sizeof(char));`, Also `*cell=(char**)malloc(n*sizeof(int*));` --> `*cell=malloc(n*sizeof(char*));` — BLUEPIXY, Nov 17 '16 at 04:46
`cell[i-1][j] = (char) buffer[j];` --> `cell[i][j] = buffer[j];` — BLUEPIXY, Nov 17 '16 at 04:51
@BLUEPIXY Thank for the changes to the memory allocation, but my 2D array isn't printing out anything. I think it isn't getting the values of buffer. — JClutch, Nov 17 '16 at 05:09
@BLUEPIXY Changed it to < 0, and editted the test content and name, but it still didn't work. — JClutch, Nov 17 '16 at 05:30
Use 10 (`12 10`) instead of counting rows. Because You have read to the end of the file. BTW 10 does not match the actual data row. Why is that? — BLUEPIXY, Nov 17 '16 at 05:38
@BLUEPIXY 12 is the amount of columns and 10 is rows, I haven't actually editted in the whole test file, but there are more rows with o's and dots. I am unsure of what you mean by use 10. — JClutch, Nov 17 '16 at 05:44
If you read all the files to count lines, There is no data to be read. — BLUEPIXY, Nov 17 '16 at 05:45
There are no 2D arrays in your code. Just messy three star programming. Please read [How do I correctly set up, access, and free a multidimensional array in C?](http://stackoverflow.com/questions/12462615/how-do-i-correctly-set-up-access-and-free-a-multidimensional-array-in-c). — Lundin, Nov 17 '16 at 09:09

score 1 · Accepted Answer · answered Nov 17 '16 at 06:06

fix like this:

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

void tester(char *s, int *cols, int *rows){
    int cnt;

    cnt = sscanf(s, "%d %d", cols, rows);
    if(cnt != 2 || *cols < 2 || *cols > 20 || *rows < 2 || *rows > 20){
        printf("Incorrect Matrix Dimensions!\n");
        exit(EXIT_FAILURE);//The program can not be continued.
    }
}

void allocateMem(char ***cell, int n, int m){
    *cell = malloc( n * sizeof(char*));
    for(int i = 0; i < n; i++)
        (*cell)[i] = malloc(m * sizeof(char));
}

int main(void){
    char buffer[200] = "";
    char **cell;
    int max_row, max_col;
    int i, j;

    fgets(buffer, sizeof buffer, stdin);//read first line
    tester(buffer, &max_col, &max_row);//If fgets fails, this also fails

    allocateMem(&cell, max_row, max_col);

    for(i = 0; i < max_row; ++i){
        for(j = 0; j < max_col; j++){
            int ch = fgetc(stdin);
            if(!isspace(ch))
                cell[i][j] = ch;
            else
                --j;//cancel this turn
        }
    }
    for (i = 0; i < max_row; i++){
        for (j = 0; j < max_col; j++){
            printf("%c", cell[i][j]);
        }
        puts("");//put newline
    }
    //deallocate cell
}

Segmentation Fault (core dumped) when allocating memory for 2D array

1 Answers1