Comparing string in C

Question

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

int main()
{
char array1 [50];
char array2 [50];
printf("enter a string:\n");
fgets(array1, 50, stdin);
printf("enter a string2:\n");
fgets(array2, 50, stdin);
if (array1==array2){
    printf("True");
}

}

If I enter the same string twice this code should print true. However it doesn't. How do I fix this?

Arrays are pointer. Your `==` compares the address locations and not the char elements — Micka, Apr 11 '14 at 18:50
@Micka: No, arrays are not pointers. Read section 6 of the [comp.lang.c FAQ](http://www..c-faq.com). You're correct that `array1==array2` does a pointer comparison, but only because the array expressions are *converted* to pointers. — Keith Thompson, Apr 11 '14 at 18:52
use the function [strncmp](http://www.cplusplus.com/reference/cstring/strncmp/). This link is for C++, but works the same in C. — eventHandler, Apr 11 '14 at 18:53
yeah that's better. i was comparing some kind of strings yesterday using strncmp. got confused. [strcmp](http://www.cplusplus.com/reference/cstring/strcmp/) suits better for this. — eventHandler, Apr 11 '14 at 18:56
Shall it be a byte-string, aka no interpretation except for the terminator, or text in some encoding like UTF-8? — Deduplicator, Apr 11 '14 at 19:00

a5hk · Answer 1 · 2014-04-11T18:58:15.657

2

To compare strings you can use strcmp it is defined in string.h

array1 and array2 are pointers to the start of the strings. thus this code array1==array2 compares pointers not the strings.

edited Apr 11 '14 at 18:58

answered Apr 11 '14 at 18:49

a5hk

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score 1 · Answer 2 · edited Jun 20 '20 at 09:12

1

Use strcmp like

 if (!strcmp(array1,array2))
    printf("true\n");

See strcmp(3)

Your comparison array1 == array2 is comparing addresses (so does not work).

edited Jun 20 '20 at 09:12

Community

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answered Apr 11 '14 at 18:51

Basile Starynkevitch

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IMHO `if (strcmp(array, array2) != 0)` is clearer. – Keith Thompson Apr 11 '14 at 18:53

score 1 · Answer 3 · answered Apr 11 '14 at 18:51

You are comparing the two pointers to the memory location of the arrays.

You can use strcmp:

if (strcmp(str1,str2) == 0) {
    printf("they match!");
}

Or in more detail, you need to compare the value of each entry in the arrays:

int i;
int match = 1;
for (i = 0; i < 50; i++) {
    if (array1[i] != array2[i]) {
        match = 0;
        break;
    }
}
if (match == 1) {
    printf("They match");
} else {
    printf("They do not match");
}

score 0 · Answer 4 · answered Apr 11 '14 at 18:50

0

You're comparing two pointers there. You want strncmp(array1, array2, 50) == 0

answered Apr 11 '14 at 18:50

Salgar

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score 0 · Answer 5 · answered Apr 11 '14 at 18:50

You should use strcmp or strncmp.

For example:

int result = strncmp(string1, string2, compareLimit);, where compareLimit is the number of characters to compare to.

The result will inform you on equality 0 or whether string1 is greater than, or less than string2.

Deduplicator · Answer 6 · 2014-04-11T18:59:05.520

0

It depends on what you mean by the same. Do you want the exact same byte sequence, or a locale-dependend comparison?

The first one is handled be strcmp(), the second calls for strcoll(). Both are in <string.h>.

edited Apr 11 '14 at 18:59

answered Apr 11 '14 at 18:51

Deduplicator

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Comparing string in C

6 Answers6