Remove substring of string

Question

So i was doing some coding exercice on Talentbuddy (for those who know), and i cant get why i cant finish this one. The exercice is removing a substring from a string, given as input the string, the position P where beginning to remove characters and N the number of characters needed to be remove.

Here is what i've done :

#include <stdio.h>
#include <unistd.h>

void remove_substring(char *s, int p, int n) 
{
    int idx;

    idx = -1;
    while (s[++idx] != '\0')
       write(1, &s[idx == p - 1 ? idx + n : idx], 1);
}

When the input is "abcdefghi", P = 9 and N = 1, the result given is "abcdefgh" exactly the same as the one i get with my function. But TalentBuddy keep saying me that my output is wrong and i dont thing he (talentbuddy) is wrong. Maybe there is a blank space or something between the "h" and the '\0'. But i cant figure it cause when i add another write(1, "END", 3) at the end it appears like "abcdefghEND".

Use a debugger to step through your code. The importance of being able to debug effectively cannot be overstated. — dandan78
– dandan78, Commented Sep 9, 2014 at 15:40
Hey Robin, I'm your boss, and you're fired for playing with Talentbuddy during work hours :) — xlecoustillier
– xlecoustillier, Commented Sep 9, 2014 at 15:45
Why are you using write to output to stdout? Why not just use printf or puts? And it's unclear what you're saying your problem is. — lurker
– lurker, Commented Sep 9, 2014 at 15:46
What is your question? If you get the required result then what's the problem? — interjay
– interjay, Commented Sep 9, 2014 at 15:46

asio_guy · Accepted Answer · 2016-10-12 03:29:29Z

1

If the question is exclusively for strings( NULL Terminated ) Why can't this be as simple as this, unless it is a homework.

void removesubstr( const char *string, const char *substring )
{
        char *p = strstr(string, substring);
        if(p)
        {
                strcpy(p,p+strlen(substring));
        }
}

answered Oct 12, 2016 at 3:29

asio_guy

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Comments

M Oehm · Accepted Answer · 2014-09-09 16:19:27Z

Your problem is that you write something for every original index, even if it should be suppressed. What you write looks like abcdefgh, but it is abcdefgh<nul>, where the terminal doesn't render the <nul>.

You are mixing two methods here. Either filter out the removed substring:

void remove_substring(char *s, int p, int n) 
{
    int i = 0;

    p--;        /* convert to C-style index */

    while (s[i] != '\0') {
       if (i < p || i >= p + n) putchar(s[i]);
       i++;
    }
}

or skip the substring by jumping over it:

void remove_substring(char *s, int p, int n) 
{
    int i = 0;
    int l = strlen(s);

    while (i < l) {
        if (i + 1 == p) {
            i += n;
        } else {
            putchar(s[i++]);
        }
    }
}

You're trying to do a bit of both.

(I've avoided the awkward combination of prefix increment and starting at minus 1. And I've used putchar instead of unistd's write. And the termination by length is so you don't inadvertently jump beyond the terminating <nul>.)

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