CODEWITHSUNDEEP
carrayshexbit-shift
Eric Horng
Eric Horng

Reputation: 57

Converting an int to uint8_t array HEX value

I'd like to take an int, and convert it into uint8_t array of hex numbers? The int is at maximum 8 bytes long in HEX after conversion. I was able to use a method that converts an int (19604) into a uint8_t array like this:

00-00-00-00-00-00-00-00-04-0C-09-04

But I need it to look like this:

00-00-00-00-00-00-00-00-00-00-4C-94

The algorithm I used was this:

void convert_file_size_to_hex(long int size)
{
    size_t wr_len = 12;
    long int decimalNumber, quotient;
    int i=wr_len, temp;

    decimalNumber = size;
    quotient = decimalNumber;
    uint8_t hexNum[wr_len];
    memset(hexNum, 0, sizeof(hexNum));

    while(quotient != 0) {
        temp = quotient % 16;
        hexNum[--i] = temp;
        quotient /= 16;
}

How can I go about doing this? Should I use a different algorithm or should I try to bit shift the result? I'm kinda new to bit shifting in C so some help would be great. Thank you!

Upvotes: 2

Views: 5925

Answers (3)

Ray Hamel
Ray Hamel

Reputation: 1309

Use a union for this

union int_to_bytes {
        int i;
        uint8_t b[sizeof(int)];
};

union int_to_bytes test = { .i = 19604 };

int i = sizeof(test.b); // Little-Endian
while (i--)
        printf("%hhx ", test.b[i]); // 0 0 4c 94

putchar('\n');

Upvotes: 0

Mike
Mike

Reputation: 167

Consider the following code:

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

int main()
{
    unsigned char hexBuffer[100]={0};
    int n=19604;
    int i;

    memcpy((char*)hexBuffer,(char*)&n,sizeof(int));

    for(i=0;i<4;i++)
        printf("%02X ",hexBuffer[i]);

    printf("\n");

    return 0;
}

Use just a simple statement to convert int to byte buffer 

memcpy((char*)hexBuffer,(char*)&n,sizeof(int));

You can use 8 instead of 4 while print the loop

Upvotes: 1

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726559

Since n % 16 has a range of 0..15, inclusive, you are making an array of single hex digits from your number. If you would like to make an array of bytes, use 256 instead:

while(quotient != 0) {
    temp = quotient % 256;
    hexNum[--i] = temp;
    quotient /= 256;
}

You can rewrite the same with bit shifts and bit masking:

while(quotient != 0) {
    temp = quotient & 0xFF;
    hexNum[--i] = temp;
    quotient >>= 8;
}

To know how many bytes you need regardless of the system, use sizeof(int):

size_t wr_len = sizeof(int);

Upvotes: 1

Related Questions