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Initialization of variables sized arrays in C

  • Difficulty Level : Easy
  • Last Updated : 28 Sep, 2018

The C99 standard allows variable sized arrays (see this). But, unlike the normal arrays, variable sized arrays cannot be initialized.

For example, the following program compiles and runs fine on a C99 compatible compiler.




#include<stdio.h>
  
int main()
{
  int M = 2;
  int arr[M][M];
  int i, j;
  for (i = 0; i < M; i++)
  {
    for (j = 0; j < M; j++)
    {
       arr[i][j] = 0;
       printf ("%d ", arr[i][j]);
    }
    printf("\n");
  }
  return 0;
}

Output:

0 0
0 0

But the following fails with compilation error.




#include<stdio.h>
  
int main()
{
  int M = 2;
  int arr[M][M] = {0}; // Trying to initialize all values as 0
  int i, j;
  for (i = 0; i < M; i++)
  {
    for (j = 0; j < M; j++)
       printf ("%d ", arr[i][j]);
    printf("\n");
  }
  return 0;
}

Output:

Compiler Error: variable-sized object may not be initialized

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

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