Accessing 2D array values using a pointer

Question

I need to take a 2d array (Grid) from stdin, do some manupulation to the chars and print a new grid with the changes.

My strategy was to make a Struc with a Grid grid[LINES][COLUMNS] then use getChar() to push each char into grid using a pointer. It work great when I print within the function but I can't acces the values from outside. I am only getting weird characters that probably represent memory adress or something.

Here is a simplified code block of the program.

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

struct Grid{                          
    char box[20][40]; 
};


int main(int argc, char *argv[]) {
    struct Grid grid;

    readInitGrid(&grid);
    displayGrid(&grid);

}

void readInitGrid(struct Grid *grid) {
  char c;
  for (unsigned int i = 0; i < 20; i++) {
    for (unsigned int j = 0; j < 40 + 1; j++) { //+1 is for the /n at the end of each line
      while ((c = getchar()) != EOF) {
        grid->box[i][j] = c;
        printf("%c", grid->box[i][j]);     //Will print correcly
      }
    }
  }
}

void displayGrid(const struct Grid *grid) {
  for (unsigned int i = 0; i < 20; ++i) {
      for (unsigned int j = 0; j < 40; ++j) {
          printf("%c", grid.box[i][j]);       //This do not work
      }
  }
  printf("\n");
}

Result - See both print block bellow First block show perfectly but second is messed-up

I am passing other things to this struct in the real program and I dont have any issu to acces the infomration for int and char. THe only one I am having issue with is 2d array. An other thing, I can't use maloc for this.

Fixed Thank you @xing

CareFace
– CareFace

2017-10-14 23:13:35 +00:00
Commented Oct 14, 2017 at 23:13 — CareFace
– CareFace, Commented Oct 14, 2017 at 23:13
Ok did it. Sorry it is my first time using stackoverflow.

CareFace
– CareFace

2017-10-15 19:13:50 +00:00
Commented Oct 15, 2017 at 19:13 — CareFace
– CareFace, Commented Oct 15, 2017 at 19:13

CareFace · Accepted Answer · 2017-10-15 19:13:13Z

1

Changed the while to an if so that my for loop affect the grid->box[i][j] = c;

void readInitGrid(struct Grid *grid) {
  char c;
  for (unsigned int i = 0; i < 20; i++) {
    for (unsigned int j = 0; j < 40 + 1; j++) { 
      if ((c = getchar()) != EOF) {
        grid->box[i][j] = c;
        printf("%c", grid->box[i][j]);    
      }
    }
  }
}

answered Oct 15, 2017 at 19:13

CareFace

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