CODEWITHSUNDEEP
cstrcmpstring.h
user3540997
user3540997

Reputation: 59

I do not understand strcmp results

this is my implementation of strcmp ,

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

   int ft_strcmp(const char *s1, const char *s2)
   {
       while (*s1 == *s2)
       {
           if (*s1 == '\0')
              return (0);
          s1++;
          s2++;
      }
      return (*s1 - *s2);
  }

  int main()
  {
      char    s1[100] = "bon";
      char    s2[100] = "BONN";
      char    str1[100] = "bon";
      char    str2[100] = "n";
      printf("%d\n", ft_strcmp(s1, s2));
      printf("%d\n", ft_strcmp(str1, str2));
      return (0);
  }

from the book kernighan and Ritchie but i use a while loop, instead of the for, i ve tested it many times and my strcmp geaves the same results as the original strcmp, but i do not understand the results , i rode the man: "The strcmp() and strncmp() functions lexicographically compare the null-terminated strings s1 and s2." what does lexicography means ? "return an integer greater than, equal to, or less than 0, according as the string s1 is greater than, equal to, or less than the string s2." i understand this part but my questions are how can it come up with such results:

32
-12

s1 looks < s2 for me so how and why do i get 32 and how the calcul is made ? str1 looks > str2 for me, how and why do i get -12 and how the calcul is made. I ve compile it with the real STRCMP and i get the Same results..

last question why do i need to compare *s1 to '\0' won't it work fine without ?

thank you for your answers i m confused..

Upvotes: 3

Views: 2156

Answers (4)

alfred mokgohloa
alfred mokgohloa

Reputation: 1

int ft_strcmp(char *s1,char *s2)
{
    int x;

    x = 0;
    while(s1[x] != '\0' && s2[x] != '\0' && s1[x] == s2[x])
        i++;
    return (s1[x] - s2[x]);
}

by mokgohloa ally

Upvotes: 0

user3540997
user3540997

Reputation: 59

SO we compare *s1 to '\0' to see when does the string ends, and the results are made using the decimal value of the first characteres of each string.

Upvotes: 0

VHarisop
VHarisop

Reputation: 2826

Capital letters in terms of ASCII codes actually precede lowercase letters, as you can see here.

So in terms of lexicographic ordering, s1 is treated as being bigger than s2, because the ascii value of the first letter that differs is the larger one.

Upvotes: 1

uraimo
uraimo

Reputation: 19821

1) K&R are comparing the ascii values of those chars, that's why you get 32 and -12, check out an ascii table and you'll understand.

2)If you don't check for \0 , how can you know when the string end? That's the c strings terminator.

Upvotes: 3

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