compare two arrays of different types

Question

I want to compare to array. My problem is, that the first array is an array with this structure: 00d5ff4l (a mac-address without colon). The second array is from a buffer. His structure is 00 d5 ff 41 (Hex)

My current code looks like this

char mac[] = "00d5ff4l";
for (int i = 0; i < sizeof(mac); i++) {
    if (mac[i] != other_array[i]) {
        return 0;
    }
    else
        return 1;
}

Now is the problem the following: Index 1 of mac is '0', but for other_array it's '00'. So it will never match in this way. Do i have to cast one of them? If yes, how?

Related: https://stackoverflow.com/questions/3408706/hexadecimal-string-to-byte-array-in-c — Caramiriel, Jun 21 '17 at 19:12
Not cast but convert to a comparable format. C won't do it automatically for you. — Eugene Sh., Jun 21 '17 at 19:13
If this doesn't work, then you will have to write your own function. If "00" goes down to 0, then "01:00:00" will go down to "100", and you'll have to distinguish it from "01:00" manually. — Alex, Jun 21 '17 at 19:18
Read [ask] and provide a [mcve]. Don't write a novel to explain your code (or what you think your code does). — too honest for this site, Jun 21 '17 at 19:22
Should the compare "00d5ff4l" match "00 D5 FF 41"? (case consideration) — chux - Reinstate Monica, Jun 21 '17 at 21:23

score 1 · Accepted Answer · answered Jun 21 '17 at 20:11

Here's a little working utility function for you using strncmp

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

int compare_mac() {
    char mac[] = "00d5ff4l";    
    char other_array[] = "00:d5:ff:4l"; //Will work for "00 d5 ff 4l" as well
    int i = 0;
    int j = 0;

    //Bail out early for invalid inputs
    if(strlen(other_array) - strlen(mac) !=3){
        printf("Not Equal");
        return -1;        
    }

    while(i < strlen(mac)){
        if(strncmp(mac+i, other_array+j,2 ) !=0){
            printf("Not Equal");
            return -1;
        }
        i=i+2;
        j=j+3;
    }
    printf("Equal MAC IDs");

    return 0;
}

Discalaimer:- strncmp requires 2 non null pointers. The behavior is undefined when access occurs past the end of either array. The behavior is undefined when either param is a null pointer. So do adequate safety measures if you are taking the char arrays as in params to the function

score 0 · Answer 2 · answered Jun 22 '17 at 05:01

0

I propose to use if statement only, because mac adress will not changed for several years)) Just create if() conditional for all 8 elements in array. It will be fastest solution without any conversion or loops.

answered Jun 22 '17 at 05:01

OVelychko

49
3

compare two arrays of different types

2 Answers2