How do I compare two string in C?

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Hi, I want to compare two string and find out how much this two strings are similar.
strcmp is not a good idea I think.
for example we have 3 strings. I need to find out similarity of string 1 and 2 is higher or similarity of string 1 and 3. Any Idea?

I want this for comparing two packet's payload.

thanks

Do we have such compare function in c?

What I have tried:

string str1 = "I am string number one"
string str2 = "I am string number two"
string str3 = "this is string number 3"
int similarity12,similarity13;
similarity12 = compare(str1,str2);
similarity13 = compare(str1,str3);

Posted 22-Apr-17 2:21am

Member 11112168

Updated 22-Apr-17 3:04am

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PIEBALDconsult · Answer 1 · 2017-04-22T03:04:00

Solution 1

It sounds like you might want Levenshtein distance - Wikipedia[^]

Posted 22-Apr-17 3:04am

PIEBALDconsult

Comments

Member 11112168 22-Apr-17 9:25am

Can we use levenshtein for assessing packet payload similarity?

PIEBALDconsult 22-Apr-17 10:28am

It's just bytes. :)
Try it and see.

Member 11112168 23-Apr-17 1:32am

In the code when I want to print the result I get "illegal write, out of bounds error"

#define MIN3(a, b, c) ((a) < (b) ? ((a) < (c) ? (a) : (c)) : ((b) < (c) ? (b) : (c)))
static void levenshtein(char *s1, char *s2) {
      int x, y, s1len, s2len,similarity;
    s1len = strlen(s1);
    s2len = strlen(s2);
	printf("string1= %s \nstring2= %s \n",s1,s2);
      int matrix[s2len+1][s1len+1];
    matrix[0][0] = 0;

    for (x = 1; x <= s2len; x++)
        matrix[x][0] = matrix[x-1][0] + 1;
  for (y = 1; y <= s1len; y++)
        matrix[0][y] = matrix[0][y-1] + 1;
      for (x = 1; x <= s2len; x++)
        for (y = 1; y <= s1len; y++)
            matrix[x][y] = MIN3(matrix[x-1][y] + 1, matrix[x][y-1] + 1, matrix[x-1][y-1] + (s1[y-1] == s2[x-1] ? 0 : 1));
        similarity = matrix[s2len][s1len];
       printf("payload similarity= %d \n", similarity) ;  
}

PIEBALDconsult 23-Apr-17 13:44pm

Seems to work for me.
Did you use a debugger to step through the code to be sure you know where the problem (if any) is?
And which compiler are you using?

Member 11112168 25-Apr-17 3:05am

I use this code in Contiki Cooja. I used another algorithm for Levenstien.thanks