CODEWITHSUNDEEP
carrayscompareintc99
user1083734
user1083734

Reputation: 5195

Best way to compare two int arrays of the same length?

what is the best way to compare int arrays b and c with a:

int a[] = {0,1,0,0,1};
int b[] = {0,1,0,0,1};
int c[] = {1,1,0,0,1};

b and c are just examples, assume they can be any combination of 0s and 1s.

I am trying to detect arrays identical to a. I have googled this for a while and have not found a satisfactory answer.

This is a beginners question I realise, thank you for your patience.

Upvotes: 14

Views: 43529

Answers (5)

pennyloafers
pennyloafers

Reputation: 70

For performance reasons memcmp() will compare byte for byte while int arrays are in 4 byte chunks. This will most likely be pretty slow if the array is large or you have to compare many arrays.

The simplest way is to run a for loop that exits as soon as you find a difference.

bool is_array_equal(const int * a, const int * b, length){
    for (int i = 0; i < length; ++i){
        if(a[i] != b[i]){ return false; }
    }
    return true;
}

Upvotes: 0

Lax
Lax

Reputation: 41

More information is needed on the question. I can divide your question in two ways as below,

  1. Compare array contents considering order?? Ex:char a[]={a, b, c}, b[]={a, c, b} here since you are considering the order, the contents are not same so a!=b
  1. compare array contents irrespective of order? Ex:char a[]={a, b, c}, b[]={a, c, b} here if you are not considering the order, the contents are same so a==b

Solution for Question no 1: One can use memcmp for this problem. Because memcmp will compare lexicographical and return 0 or 1 or -1 as below

 #include<stdio.h>
    #include<string.h>
    int main()
    {

        char a[]={'a','b','c'};
        char b[]={'a','b','c'};
        int x=memcmp(a,b,sizeof(a));
        printf("%d\n",x);

    return 0;
    }
***output:0***

    #include<stdio.h>
    #include<string.h>
    int main()
    {

        char a[]={'a','c','b'};
        char b[]={'a','b','c'};
        int x=memcmp(a,b,sizeof(a));
        printf("%d\n",x);

    return 0;
    }
***output:1***

    #include<stdio.h>
    #include<string.h>
    int main()
    {

        char a[]={'a','b','c'};
        char b[]={'b','a','c'};
        int x=memcmp(a,b,sizeof(a));
        printf("%d\n",x);

    return 0;
    }
***output:-1***

Solution for Question no 2: One can use memcmp for this problem, the best solution for this problem is as below

Here, I answered for the above problem https://stackoverflow.com/a/36130812/5206646

Upvotes: 1

Useless
Useless

Reputation: 67822

If you mean

int a[] = {0,1,0,0,1};
int b[] = {0,1,0,0,1};
int c[] = {1,1,0,0,1};

then

memcmp(a, b, sizeof(a)); /* returns zero for a match */
memcmp(a, c, sizeof(a)); /* returns nonzero for no match */

Upvotes: 6

sth
sth

Reputation: 229894

Use a loop and compare the individual elements one after another.

Upvotes: 5

Fred Foo
Fred Foo

Reputation: 363817

Use the standard memcmp function from <string.h>.

memcmp(a, b, sizeof(a)) == 0

whenever a and b are equal.

Upvotes: 33

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