Why do two strings, when compared with the equals == operator, not match up even if the output is the same?

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How to compare strings in an “if” statement?

I'm using C. My two strings, when compared with the equals == operator, are not matching up, even if the std output looks the same.

Consider one of the arrays started as an array of integers, which I converted to characters by adding a '0' to each integer and loading into another char * array.

So now both arrays are character arrays with characters and the same std output, but my "if" selection structure is not working to match them. I am using the char * name to reference each array.

I could post this entire code if necessary. Here is a loop with the comparison:

i=0;
pipx = (char*)malloc(sizeof(char));
sec = (char*)malloc(sizeof(char));

//for (b = 0; b < lengthx; b++){
    //reallocate a second array
    pipx = (char*)realloc(sec, ((i+1)*sizeof(char)) );
    sec = pipx;
    //add bitstr[b] to second array
    sec[i] = (char)bitstr[b] + '0';
    i++;

    for (m = 0; m < k; m++){
        printf("codex[m].bitx:%s", codex[m].bitx);
        printf("sec:%s|\n", sec);
        printf("seclen: %i", (int)strlen(sec));
        printf("codex[m].bitxlen: %i\n", (int)strlen(codex[m].bitx));
        if ((char*)sec == (char*)codex[m].bitx){
            printf("This should output: %s", sec);
            printf("Here ---------------------- Here");
            //allocate the second array to zero
            i=0;
            sec = (char*)malloc(0);
        }
    }
}

This question has been asked many times before. You might find an explanation in [this one](http://stackoverflow.com/questions/12593115/c-string-comparison-equates-to-true), asked an hour ago with a little bit of depth beyond just this. — chris, Sep 26 '12 at 01:47
@WiSaGaN No, the OP is turning bits -- 0 or 1 -- into characters. Adding '\0' would be a no-op. — Jim Balter, Sep 26 '12 at 05:59

score 4 · Answer 1 · answered Sep 26 '12 at 01:47

4

in order to compare strings, you need to use strcmp instead of ==

== verifies they point to the same address, while strcmp will compare the two char* and return true if every character matches until it hits \0

answered Sep 26 '12 at 01:47

Majid Laissi

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Yes this works, c is new to me, very helpful! – Netmaxweb Sep 26 '12 at 03:31

score 1 · Answer 2 · answered Sep 26 '12 at 01:48

1

That's because you are comparing to see if the two variables point to the same memory address, not if the information at the two memory addresses is the same. always use strcmp

answered Sep 26 '12 at 01:48

Ionut Hulub

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score 0 · Answer 3 · answered Sep 26 '12 at 01:49

0

You are comparing literal pointer values rather than the strings those pointers point to.

As others have said, lookup strcmp() and friends.

answered Sep 26 '12 at 01:49

John3136

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Why do two strings, when compared with the equals == operator, not match up even if the output is the same?

3 Answers3