Member Avatar for blerina12

Hi guys. I was wondering if you could help me with this problem. I am trying to pass a dynamic array to a function for finding the length

int length(char ** t, int i) { int count = -1; do count++; while (t[i][count] != '\0'); return count; }

The function always returns a zero value.
As a result the following code for copying the values of arrays doesnt work either

class KMP : public StM { public: KMP(); KMP(char **, char *, int index, int sz); // ~KMP(); virtual int operator ++(); char ** pattern; int * prefix; int index; }; KMP::KMP(char ** p, char * t, int i, int size) { text = t; pattern = new char*[size]; pattern = p; ( pattern[i] = new char[length(p, i)] )= p[i]; index = i; patlen = length(p, i); prefix = new int[patlen]; prefix[0] = 0; for(int i=1; i < patlen; i++) { int k = prefix[i-1]; while ((pattern[i] != pattern[k]) && (k != 0)) {k = prefix[k-1]; /*count++;*/} if(pattern[i] == pattern[k]) prefix[i] = k+1; else prefix[i] = 0; //count++; } } int KMP::operator ++() { int mp = length(text); int cp = pos + 1; int pp = 0; for(; cp < mp; cp++) { while( (pp>0) && (pattern[index][pp] != text[cp]) ) {pp = prefix[pp-1]; count++;} if(pattern[index][pp] == text[cp]) { pp++; if(pp == patlen){position(1+cp-patlen); cout << pos << "\t"; } } count++; } position(-1); return 0; }

If there is antything wrong with the code please point it out, or maybe if you know about a function that copies values from a dynamic array to a static one please let me know. thanks

  • 2 Contributors
  • 2 Replies
  • 325 Views
  • 20 Hours Discussion Span
  • Latest Post Latest Post by blerina12
Member Avatar for ArkM

Please, explain these evidently wrong statements:

pattern = new char*[size]; pattern = p; ( pattern[i] = new char[length(p, i)] )= p[i];

See what happens:
- You create uninitialized array of pointers to char.
- The next statement overwrite a pointer to this array (memory leak) by the parameter p value.
- The 3rd statement is the most interesting because it do the same destructive performance in all-in-one manner: it allocates a memory chunk of undefined size (no check for length(...) <= 0) then save an obtained pointer value to pattern[i] element then (immediately) overwrite this value by p[i] . Thank God, the effect of "only even number of errors gets correct result" principle works: pattern and p pointers points to the same memory (see statements above ;)...

Member Avatar for blerina12

Please, explain these evidently wrong statements:

pattern = new char*[size]; pattern = p; ( pattern[i] = new char[length(p, i)] )= p[i];

See what happens:
- You create uninitialized array of pointers to char.
- The next statement overwrite a pointer to this array (memory leak) by the parameter p value.
- The 3rd statement is the most interesting because it do the same destructive performance in all-in-one manner: it allocates a memory chunk of undefined size (no check for length(...) <= 0) then save an obtained pointer value to pattern[i] element then (immediately) overwrite this value by p[i] . Thank God, the effect of "only even number of errors gets correct result" principle works: pattern and p pointers points to the same memory (see statements above ;)...

Thanks a lot. That solved the problem. :)

Be a part of the DaniWeb community

We're a friendly, industry-focused community of developers, IT pros, digital marketers, and technology enthusiasts meeting, networking, learning, and sharing knowledge.