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This article will demonstrate various ways of initializing a character array in C language.

{}Initializing a character array in C using curly brace list notation

Character arrays are mostly declared as a fixed-size structure and are often initialized immediately. The brace list notation is one of the available ways to initialize a character array with a constant value. You can specify only some of the elements enclosed in the braces because the rest of the character array is implicitly initialized with a null byte value. This is useful if you need to print a character array as a string. Since there is guaranteed to be a null byte character at the end of the valid characters, you can effectively use printfthe functions and %sformat string specifiers to output the contents of the array.

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

void printCharArray(char *arr, size_t len)
{
    printf("arr: ");
    for (int i = 0; i < len; ++i) {
        printf("%c, ", arr[i]);
    }
    printf("\n");
}

enum {LENGTH = 21, HEIGHT = 5};

int main(){
    char c_arr[LENGTH] = {'a', 'b', 'c', 'd', 'e', 'f', 'g'};
    printCharArray(c_arr, LENGTH);

    exit(EXIT_SUCCESS);
}

Output:

arr: a, b, c, d, e, f, g, , , , , , , , , , , , , , ,

Using string assignment to initialize character array in C

Another useful way to initialize a character array is to specify a string value in the declaration statement. The number of characters in the string should be less than the length of the array; otherwise, only part of the string will be stored and there will be no terminating null character at the end of the buffer. Therefore, if the user tries %sto print the contents of the array with the specifier, it may access the memory area after the last character and may throw a fault.

Note c_arrthat is 21 characters long and is initialized to a 20 charlong string. Therefore, the 21st character in the array is guaranteed to be \0a byte, making the contents a valid string.

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

void printCharArray(char *arr, size_t len)
{
    printf("arr: ");
    for (size_t i = 0; i < len; ++i) {
        printf("%c, ", arr[i]);
    }
    printf("\n");
}

enum {LENGTH = 21, HEIGHT = 5};

int main(){
    char c_arr[LENGTH] = "array initialization";
    char c_arr2[LENGTH] = "array initialization.f";
    printCharArray(c_arr, LENGTH);
    printCharArray(c_arr2, LENGTH);
    printf("%s\n", c_arr);
    printf("%s\n", c_arr2);

    exit(EXIT_SUCCESS);
}

Output:

arr: a, r, r, a, y,  , i, n, i, t, i, a, l, i, z, a, t, i, o, n,  ,
arr: a, r, r, a, y,  , i, n, i, t, i, a, l, i, z, a, t, i, o, n, .,
array initialization
array initialization.//garbage values//

{{ }}Initializing 2D character array in C using double curly braces

Brace lists can also be used to initialize two-dimensional character arrays. In this example, we declare a 5x5 character array and enclose five braces in outer braces. Note that each string literal in this example initializes five rows of the matrix. The contents of this two-dimensional array cannot %sbe printed with the specifier because the length of each row matches the length of the string literal; therefore, no terminating null byte is implicitly stored during initialization. Normally, the compiler issues a warning if the length of the string is greater than the number of rows in the array.

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

enum {LENGTH = 5, HEIGHT = 5};

int main(){
    char c_arr[HEIGHT][HEIGHT] = { {"hello"}, {"there"}, {"multi"}, {"dimen"}, {"sion."} };

    for (size_t i = 0; i < HEIGHT; ++i) {
        for (size_t j = 0; j < HEIGHT; ++j) {
            printf("%c, ", c_arr[i][j]);
        }
        printf("\n");
    }
    printf("\n");

    exit(EXIT_SUCCESS);
}

Output:

h, e, l, l, o,
t, h, e, r, e,
m, u, l, t, i,
d, i, m, e, n,
s, i, o, n, .,