Initialize multidimensional arrays in C

This post will discuss how to initialize multidimensional arrays in the C programming language.

A multidimensional array is an array with more than one dimension. The simplest multidimensional array is the 2D array or two-dimensional array. It is basically an array of arrays, which is also commonly known as a matrix. The general array initialization syntax applies to multidimensional arrays as well.

1. Using Static Storage

All objects in C with static storage duration are set to 0, which were not explicitly initialized by the programmer. The following code initializes the first cell of a 6 × 8 matrix to 0, and the rest of the elements as if they had static storage duration, i.e., initialized with zero.

#include <stdio.h>

int main(void)

{

int mat[6][8] = { 0 }; // or, use {{ 0 }}

int r = sizeof(mat)/sizeof(mat[0]);

int c = sizeof(mat[0])/sizeof(mat[0][0]);

// print the matrix

for (int i = 0; i < r; i++)

{

for (int j = 0; j < c; j++) {

printf("%d ", mat[i][j]);

}

printf("\n");

}

return 0;

}

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2. Using `memset()` function

We can also use the memset() function to initialize a multidimensional array with 0 or -1. The memset() function overwrites the allocated memory of the array with 0’s or 1’s. This works with both fixed-length and variable-length multidimensional arrays.

#include <stdio.h>

#include <string.h>

int main(void)

{

const size_t R = 6;

const size_t C = 8;

int mat[R][C];

memset(mat, 0, sizeof(mat[0][0]) * R * C);

// print the matrix

return 0;

}

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3. Using standard for-loop

Finally, we can initialize a multidimensional array with any value using nested for-loops.

#include <stdio.h>

int main(void)

{

const size_t R = 6;

const size_t C = 8;

int mat[R][C];

int value = 1;

for (int i = 0; i < R; i++)

{

for (int j = 0; j < C; j++) {

mat[i][j] = value;

}

// print the matrix

return 0;

}

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C also allows multidimensional arrays to be iterated through by a base-element pointer. So, we can do something like:

for (int i = 0; i < R*C; i++) {

*((int*)mat + i) = 0;

}

Note that the global and static arrays are initialized with their default values when no initializer is specified. For instance, a global integer array will be zero-initialized by default.

That’s all about initializing multidimensional arrays in C.

Also See:

Initialize a matrix in C++

Initialize multidimensional arrays in C

1. Using Static Storage

2. Using memset() function

3. Using standard for-loop

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2. Using `memset()` function