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Initialization of variables sized arrays in C

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