CODEWITHSUNDEEP
cstringstrlen
Michael Stevens
Michael Stevens

Reputation: 222

cannot get the length of a string through strlen in other function?

I am making a function in C which removes any duplicates form a string.
If I run this code and provide the index in main() function it works.

char *clean(char *list, int index) {
    int val = 0;
    char temp_list[index];
    for (int i = 0; i < index; i++) {
        if (list[i] != list[i + 1]) {
            temp_list[val] = list[i];
            val += 1;
        }
    }
    for (int y = 0; y < val; y++) {
        list[y] = temp_list[y];
    }
    return list;
}

But if I run this code it doesn't seem to work.

char *clean(char *list) {
    int index = strlen(list);
    int val = 0;
    char temp_list[index];
    for (int i = 0; i < index; i++) {
        if (list[i] != list[i + 1]) {
            temp_list[val] = list[i];
            val += 1;
        }
    }
    for (int y = 0; y < val; y++) {
        list[y] = temp_list[y];
    }
    return list;
}

In the second code the index is always zero.
Can anyone explain me why is strlen() function not working.

Upvotes: 0

Views: 67

Answers (1)

chqrlie
chqrlie

Reputation: 144685

The problem is not where you think: you do not set the null terminator when reducing the length of the string, so the modified list still has the trailing bytes in place and reachable.

Here is a modified version without a temporary array:

#include <stddef.h>

char *clean(char *s) {
    size_t i, j;
    for (i = j = 0; s[i] != '\0'; i++) {
        if (s[i] != s[i + 1]) {
            s[j++] = s[i];
        }
    }
    s[j] = '\0';
    return s;
}

Upvotes: 1

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