Convert ASCII string (char[]) to BYTE array in C

C | Convert ASCII string to BYTE array: Here, we are going to learn how to convert a given string (that contains ascii characters) to its equivalent BYTE array in C? By IncludeHelp Last updated : April 20, 2023

Given an ASCII string (char[]) and we have to convert it into BYTE array (BYTE[]) in C.

Logic to convert an ASCII string to BYTE array

To convert an ASCII string to BYTE array, follow below-mentioned steps:

Extract characters from the input string and get the character's value in integer/number format using %d format specifier, %d gives integer (number) i.e. BYTE value of any character.
Add these bytes (number) which is an integer value of an ASCII character to the output array.
After each iteration increase the input string's loop counter (loop) by 1 and output array's loop counter (i) by 1.

Example

Input: "Hello world!"
Output:
72
101
108
108
111
32 
119
111
114
108
100
33

C program to convert ASCII char[] to BYTE array

In this example, ascii_str is an input string that contains "Hello world!", we are converting it to a BYTE array. Here, we created a function void string2ByteArray(char* input, BYTE* output), to convert ASCII string to BYTE array, the final output (array of integers) is storing in arr variable, which is passed as a reference in the function.

Note: Here, we created a typedef BYTE for unsigned char data type and as we know an unsigned char can store value from 0 to 255.

Read more: typedef in C, unsigned char in C

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

typedef unsigned char BYTE;

//function to convert string to byte array
void string2ByteArray(char* input, BYTE* output)
{
    int loop;
    int i;

    loop = 0;
    i = 0;

    while (input[loop] != '\0') {
        output[i++] = input[loop++];
    }
}

int main()
{
    char ascii_str[] = "Hello world!";
    int len = strlen(ascii_str);
    BYTE arr[len];
    int i;

    //converting string to BYTE[]
    string2ByteArray(ascii_str, arr);

    //printing
    printf("ascii_str: %s\n", ascii_str);
    printf("byte array is...\n");
    for (i = 0; i < len; i++) {
        printf("%c - %d\n", ascii_str[i], arr[i]);
    }
    printf("\n");

    return 0;
}

Output

ascii_str: Hello world!
byte array is...
H - 72
e - 101
l - 108
l - 108
o - 111
  - 32 
w - 119
o - 111
r - 114
l - 108
d - 100
! - 33