What does strcmp() exactly return in C?

Question

I wrote this code in C:

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

int main()
{
    char string1[20];
    char string2[20];
    strcpy(string1, "Heloooo");
    strcpy(string2, "Helloo");
    printf("%d", strcmp(string1, string2));
    return(0);
}

Should console print value 1 or difference between ASCII values of o and \0 character i.e. 111? On this website, it is written that this should give out put 111, but when I run it on my laptop, it shows 1. Why?

Answer 1

From the cppreference.com documentation

int strcmp( const char *lhs, const char *rhs );

Return value

• Negative value if lhs appears before rhs in lexicographical order.

• Zero if lhs and rhs compare equal.

• Positive value if lhs appears after rhs in lexicographical order.

As you can see it just says negative, zero or positive. You can't count on anything else.

The site you linked isn't incorrect. It tells you that the return value is < 0, == 0 or > 0 and it gives an example and shows it's output. It doesn't tell the output should be 111.

Answer 2

To quote the man page:

The strcmp() and strncmp() functions return an integer less than, equal to, or greater than zero if s1 (or the first n bytes thereof) is found, respectively, to be less than, to match, or be greater than s2.

In other words, you should never rely on the exact return value of strcmp (other than 0, of course). The only guarantee is that the return value will be negative if the first string is "smaller", positive if the first string is "bigger" or 0 if they are equal. The same inputs may generate different results on different platforms with different implementations of strcmp.

Answer 3

strcmp returns 'a value lesser than 0' if the string1 is alphabetically lesser than string2; zero, if they are equal; and a 'value greater than 0' if string 1 is alphabetically greater than string 2.

Answer 4

The output depends on the implementation. A decent implementation of the strcmp function would be:

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;
}

The above implementation returns -1 if s1 < s2, 1 if s1 > s2 and 0 if s1 = s2.
But usually, there is a faster version which is implemented for actual use:

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

Note that this is faster because it skips the branching which was being done previously. Therefore, we usually have the convention that a negative return value means that s1 is lexicographically smaller than s2, and a positive value means vice-versa.

Answer 5

int strcmp(const char *str1, const char *str2)

will return a value less, equal or greater than 0. If it returns 0 it means that the two strings are equal, if it returns a value minor than 0 it indicates that str1 is less than str2. If it returns a value > 0 it means that str2 is less than str1.

Your return value is 1 because "Heloooo" is one character more then "Helloo". In fact the word Helloo has 6 characters and Heloooo has 7 characters. Exactly one more char.

Answer 6

Basically, strcmp() can return the following:

• > 0 if the 2nd string is lesser than the first 1st string.

  char s1, s2;
  strcpy (s1, "helloworld");
  strcpy (s2, "world");
  int check = strcmp (s1, s2);
  

• 0 if the strings passed are same.

  char s1, s2;
  strcpy (s1, "hello");
  strcpy (s2, "hello");
  int check = strcmp (s1, s2);
  

  In this case, as strings are equal, check will have 0.

• < 0 if the first string is smaller than the second string.

  char s1, s2;
  strcpy (s1, "hello");
  strcpy (s2, "worldhello");
  int check = strcmp (s1, s2);
  

So in your case, strcmp () will return 1 as the strings are not equal.

Check out this and this tutorials about strcmp ().