Accessing an array referenced by a pointer in C

Question

I am new to programming in C and am trying to write a simple function that will compare strings. I am coming from java so I apologize if I'm making mistakes that seem simple. I have the following code:

/* check if a query string ps (of length k) appears 
     in ts (of length n) as a substring 
     If so, return 1. Else return 0
     */
int
simple_substr_match(const unsigned char *ps,    /* the query string */
                         int k,                     /* the length of the query string */
                         const unsigned char *ts,   /* the document string (Y) */ 
                         int n                      /* the length of the document Y */)
{
    int i;
    for(i = 0;i < n;i+k){
        char comp;
        comp = ts->substring(i,k);
        if (strncmp(comp, ps, k)) {
        return 1;
        }
    }
    return 0;
}

When trying to compile i get the error: request for member 'substring' in something not a structure or union.

The idea of the code is describe in the code comment but just to elaborate I am looking to see if ps occurs as a substring of ts in increments of k(length of ps).

What am I doing wrong and how can I fix it? Is there a better way of doing what I am trying to do?

No need to downvote imo. Yes, the code is wrong, and finding the bugs isn't rocket science, but he said he's new, he tried, provided a code example, and posted the error message. That's way more than many do. — Guntram Blohm
– Guntram Blohm, Commented Feb 16, 2014 at 21:48
Im coming from java so I apologize if Im making mistakes that may seem simple. I am trying to transition from java to c. — Lesha
– Lesha, Commented Feb 16, 2014 at 23:03

Avt · Accepted Answer · 2014-02-16 21:44:52Z

2

Change

for(i = 0;i < n;i+k){
    char comp;
    comp = ts->substring(i,k);
    if (strncmp(comp, ps, k)) {
    return 1;
    }
}

to

for(i = 0;i < n-k;i++){
if (!strncmp(ts+i, ps, k)) {
        return 1;
    }
}

answered Feb 16, 2014 at 21:44

Avt

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1 Comment

Lesha Over a year ago

Thank you for the help this eliminated the error I was getting but the code does not same to be accomplishing what I want. I am trying to look for ps as a substring of ts in k increments of ts. How can I modify this code to get that result?

pscs · Accepted Answer · 2014-02-16 21:49:42Z

2

ts is a char* not a class (and you're writing in C, not C++)

How about using the standard 'strstr' C function?

if (strstr(ts, ps) != NULL) {
  return 1;
} else {
  return 0;
}

answered Feb 16, 2014 at 21:49

pscs

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Comments

KooKoo · Accepted Answer · 2014-02-16 21:48:36Z

0

C doesn't have member functions. and in c++ char doesn't have a member function substring. you should use ts as an character array.

answered Feb 16, 2014 at 21:48

KooKoo

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Comments

Sturla Molden · Accepted Answer · 2014-02-16 21:54:15Z

0

Something like this?

#define simple_substr_match(ps,ts) (strstr(ts,ps) != NULL)

answered Feb 16, 2014 at 21:54

Sturla Molden

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