How to add chars to 2D array?

Question

My code:

FILE * file;

file = fopen("c://catalog//file.txt", "r");
int m,n; //size of 2d array (m x n)
fscanf(file, "%d", &m);
fscanf(file, "%d", &n);
fclose(file);

printf("Size: %d x %d\n", m, n);

// create 2d array 
char **TAB2 = new char*[m];
for (int i = 0; i < m; i++)
    char *TAB2 = new char[n];

// display 2d array 
for (int i = 0; i < m; i++){
    for (int j = 0; j < n; j++)
    {
        printf("%c ", &TAB2[i][j]);
    }
    printf("\n");
}

How fill this array with chars or string? for example text = "someting", and for array 3x5 will be:

S o m e t
h i n g ?
? ? ? ? ?

I tried: TAB2[0][0] = 's'; *&TAB2[0][0] = 's'; for one char, and this does'nt work...

Probably I badly use pointers(?). Anyone help me?

The part inside your for loop used to allocate memory for each row of character is already wrong. Should be something like TAB2[i] = new char[n]; or advance the pointer *TAB2 every time you allocate a new char array — neiht, Jan 09 '15 at 13:56
The printing stuff is also wrong. You are passing an address to printf instead of a character. (i.e. remove the &) — Diego, Jan 09 '15 at 14:13

score 2 · Accepted Answer · edited May 23 '17 at 12:05

2

The dynamic allocation array is wrong.

char **TAB2 = new char*[m];
for (int i = 0; i < m; ++i)
    TAB2[i] = new char[n];

Check this link for help.

You could try this:

#include<iostream>
using namespace std;

int main() {

  const int m = 3, n = 5;
  char **TAB2 = new char*[m];
  for (int i = 0; i < m; ++i)
      TAB2[i] = new char[n];

  char c;
  for (int i = 0; i < m; ++i) {
    for (int j = 0; j < n; ++j) {
      std::cin >> c;
      TAB2[i][j] = c;
    }
  }

  for (int i = 0; i < m; ++i) {
    for (int j = 0; j < n; ++j) {
      std::cout << TAB2[i][j];
    }
    std::cout << "\n";
  }

  // NEVER FORGET TO FREE YOUR DYNAMIC MEMORY
  for(int i = 0; i < m; ++i)
    delete [] TAB2[i];
  delete [] TAB2;

  return 0;
}

Output:

jorje
georg
klouv
jorje
georg
klouv

Important links:

edited May 23 '17 at 12:05

Community

1
1

answered Jan 09 '15 at 13:53

gsamaras

71,951
46
188
305

http://stackoverflow.com/questions/936687/how-do-i-declare-a-2d-array-in-c-using-new/936702#936702 or http://stackoverflow.com/questions/4810664/how-do-i-use-arrays-in-c – sehe Jan 09 '15 at 14:15
Oh here is my pic in the first link @sehe! haha. By the way, good links, I am editing. – gsamaras Jan 09 '15 at 14:26
You are welcome @adfgvx. Make sure you take a look at the links in my question! – gsamaras Jan 09 '15 at 14:28
@G.Samaras fix the first delete :-) – Diego Jan 09 '15 at 14:28
A bug @Diego? Tell me more please. – gsamaras Jan 09 '15 at 14:30
I think it should use the `delete[]` operator as the memory was allocated with `new[]`. – Diego Jan 09 '15 at 14:32
Yeah! Nice catch @Diego. Damn you are good! I am gonna upvote an answer of yours for this. http://stackoverflow.com/questions/983244/is-this-deallocation-correct – gsamaras Jan 09 '15 at 14:35

score 2 · Answer 2 · answered Jan 09 '15 at 13:55

2

The allocation of the array seems incorrect; it should be as follows.

char **TAB2 = new char*[m];
for (int i = 0; i < m; i++)
    TAB2[i] = new char[n];

answered Jan 09 '15 at 13:55

Codor

17,447
9
29
56

How to add chars to 2D array?

2 Answers2