JClutch JClutch - 17 days ago 5
C Question

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

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".

Answer

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
}
Comments