Crashing C Program

Question

I am trying to write an algorithm that searches a document for a particular chunk. If the chunk is found, a 1 will be returned, if not, a 0. Basically if the chunk is "abcd" and a particular length is 2, the chunk would be split into "ab" and "cd." Then search the document to see if either "ab" or "cd" is there. I think my algorithm is pretty much fine, but the program keeps crashing. I think it has to do with the strncmp, but I can't figure out how to fix it.

Here's my code:

int main( )
{
         char s1[] = "abcdef";
         char s3[] = "cd";
         size_t s1Size = strlen(s1);
         int k = 2;

         if(simple_substr_match(s3,k,s1,s1Size))
            printf("Match Found\n");
         else
            printf("No Match Found\n");
         return 0;  
}

int simple_substr_match(const unsigned char *ps, int k, const unsigned char *ts, int n)
{
        int isMatch; 
        int i;
        int j; 

        for(i=0;i<n;i++)
        {
           if(strncmp(ts[i], ps, k))
           {
              isMatch = 1; 
           }
        }

        return isMatch; 

}

Please include the exact details of the crash. Which line of code, the message, if you've used gdb to try to debug it, etc. — Matt Ball, Sep 18 '13 at 22:00
I get a warning on line 69(the strncmp line) saying "passing argument 1 of'strncmp' makes pointer from integer without a cast." — JaxJags, Sep 18 '13 at 22:06
You probably want `ts + i` and `ps + j` instead of `ts[i]` and `ps[j]`, since you want a pointer that's offset into the string and not the value of the character found there. — Dmitri, Sep 18 '13 at 22:16
The warning is being generated because you are de-referencing the character by using []. `strncmp()` expects pointers to chars rather than char values directly. Try substituting `ts[i]` for `ts + i` and `ps[j]` for `ps + j`. I have not analyzed your logic, but at least this will probably remove the warning and avoid the crash. — , Sep 18 '13 at 22:17
Fixed! Thanks guys. Just started C, so still learning about everything. — JaxJags, Sep 18 '13 at 22:20

score 0 · Answer 1 · edited Sep 19 '13 at 20:17

0

strcmp will comapre the strings

use strstr(buffer, s1) != null

http://en.cppreference.com/w/c/string/byte/strstr

edited Sep 19 '13 at 20:17

answered Sep 18 '13 at 22:01

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score 0 · Answer 2 · answered Sep 19 '13 at 01:03

0

use : if(strncmp(&ts[i], ps, k)) or if(strncmp(ts+i, ps, k))

pay attention to warnings. By using ts[i] you are derefing and comparing with value which is a char. strncmp needs an address [ with proper memory ofcourse ]

answered Sep 19 '13 at 01:03

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Crashing C Program

2 Answers2