strcmp() return values in C

Question

I am learning about strcmp() in C. I understand that when two strings are equal, strcmp returns 0.

However, when the man pages state that strcmp returns less than 0 when the first string is less than the second string, is it referring to length, ASCII values, or something else?

score 27 · Accepted Answer · answered Oct 05 '11 at 03:48

27

In this sense, "less than" for strings means lexicographic (alphabetical) order.

So cat is less than dog because cat is alphabetically before dog.

Lexicographic order is, in some sense, an extension of alphabetical order to all ASCII (and UNICODE) characters.

answered Oct 05 '11 at 03:48

Mysticial

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From this answer someone could be led to believe that strcmp() knows about unicode. That is not the case. – Prof. Falken Oct 05 '11 at 07:37
1

@Amigable Clark Kant: For unicode, I was implicitly referring to the wide character version of `strcmp()`. But yes, I get your point. – Mysticial Oct 05 '11 at 07:39

score 8 · Answer 2 · answered Oct 05 '11 at 03:45

8

A value greater than zero indicates that the first character that does not match has a greater value in the first string than in the second, and a value less than zero indicates the opposite.

answered Oct 05 '11 at 03:45

JRL

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score 6 · Answer 3 · answered Oct 05 '11 at 03:58

C99 7.21.4:

The sign of a nonzero value returned by the comparison functions memcmp, strcmp, and strncmp is determined by the sign of the difference between the values of the ﬁrst pair of characters (both interpreted as unsigned char) that differ in the objects being compared.

Note in particular that the result doesn't depend on the current locale; LC_COLLATE (see C99 7.11) affects strcoll() and strxfrm(), but not strcmp().

score 2 · Answer 4 · answered Nov 22 '12 at 11:56

2

    int strcmp (const char * s1, const char * s2)
    {
        for(; *s1 == *s2; ++s1, ++s2)
           if(*s1 == 0)
               return 0;
        return *(unsigned char *)s1 < *(unsigned char *)s2 ? -1 : 1;
    }

answered Nov 22 '12 at 11:56

Rani

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Your answer would be considerably better if you could explain _why_ this answers the question. – Ben Nov 22 '12 at 12:15
it's also wrong answer, 1/-1 doesn't conform to C standard. And you don't check before dereferencing. – Tomas Pruzina Oct 08 '14 at 09:38
On Ubuntu 14.04 gcc is not returning -1 or 1. It returns (*s1 - *s2) – Scooter Mar 27 '17 at 06:53

score -2 · Answer 5 · edited Sep 21 '13 at 10:10

-2

Look out the following program, here I am returning the value depending upon the string you have typed. The function strcmp retrun value according to ASCII value of whole string considered totally.

For eg. str1 = "aab" and str2 = "aaa" will return 1 as aab > aaa.

int main()
{
    char str1[15], str2[15];
    int n;
    printf("Enter the str1 string: ");

    gets(str1);
    printf("Enter the str2 string : ");
    gets(str2);
    n = strcmp(str1, str2);
    printf("Value returned = %d\n", n);
    return 0;
}

edited Sep 21 '13 at 10:10

pinckerman

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answered Sep 21 '13 at 09:43

Dalbir Singh

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Welcome to stackoverflow and thank you for your answer. Please notice that this question was answered over two years ago and has a decent accepted answer. Also, your answer doesn't really answer the original question. – Itay Sep 21 '13 at 10:03

strcmp() return values in C

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