CODEWITHSUNDEEP
c++
SpiderLinked
SpiderLinked

Reputation: 373

Search for string index in array C++

I tried to find the index of an element in an array....i managed to make it work with ints using the following function:

int *getIndexOfInt(int *arr, int size, int check) {
  int *result;
  int *k;
  int count = 0;
  for (int i = 0; i <= size - 1; i++) {
    if (arr[i] == check) {
      k[count] = i;
      count++;
    }

  }
  if (count > 0) {
    *result = *k;
    return result;
  } else
    cout << "Not Found";
}

However when i tried this for strings it just gave me errors (program exited with status 11) or infinite loops:

int *getIndexOfString(string *arr, int size, string check) {
    int *result;
    int *k;
    int count = 0;
    for (int i = 0; i <= size - 1; i++) {

         if (arr[i] == check) {

            k[count] = i;
            count++;
          }

    }

    if (count > 0) {

        *result = *k;
        return result;
  } 
   else cout << "Not Found";
}

Can you please tell me why and maybe help me fix the errors?

EDIT: The result variable is the array which is then used in the main function,it contains the indexes where the string was found in the given array. The k variable is just an array in which values are stored before being added into the result. The arr is the given string array the size is the givven size and the check is the string which the code will search for.

Upvotes: 0

Views: 14427

Answers (4)

Escualo
Escualo

Reputation: 42082

Others have suggested it, and here I place it for reference.

You can use the Standard Library. In particular the algorithm std::find:

#include<vector>
#include<string>
#include<iostream>
#include<algorithm>

int main() {
  std::vector<std::string> words = {"one", "two", "three", "four", "five"};
  size_t index = std::distance(words.begin(),
                               std::find(words.begin(), words.end(), "three"));
  std::cout<<"Index: "<<index<<std::endl;
}

compiled as (GCC 4.8.1 OS X 10.7.4):

g++ indices-in-array.cpp -std=c++11

output:

Index: 2

Upvotes: 2

code_fodder
code_fodder

Reputation: 16341

Edited for vector use:

std::vector<int> getIndexOfString(string *arr, int size, string check)
{
  std::vector<int> iVect;
  for (int i = 0; i <= size - 1; i++)
  {
    if (arr[i] == check)
    {
      iVect.push_back (i);
      cout << "Found at " << i << endl;
    }
  }

  if (iVect.empty)
     cout << "not found" << endl;

  return iVect;
}

Your function has too many un-initialized pointers. Are you really wanting to return an index or a pointer? You are also missing the return value for the failed case.

Upvotes: 0

tzima
tzima

Reputation: 1295

First of all, you are accessing to uninitialized memory. The weird thing is, that your first code works. However, it's probably compiler-specific (these things happens in C++ a lot).

Local variables are usually allocated on stack and C++ doesn't guarantee you any default value. Therefore, one possible explanation is that there was (on the same memory address, where your pointer is saved) another, valid, pointer. Now, when you created this local variable, it just got this "old" address and so it's accessing to some previously allocated memory. Just don't care about it at the moment and even if it works, believe us - you shouldn't rely on this. :-)

Another problem is with that returned value. How you'd use that, when you don't know size of that array? You should return something like std::vector<>, some structure or something like that. Not just pointer to an array of unknown length!

Result: Your code is way too complicated than it could be. See better solution:

#include <iostream>
#include <string>
#include <vector>

std::vector<int> getIndexes(std::vector<std::string> &input, std::string searched) {
    std::vector<int> result;

    for (int i = 0; i < input.size(); i++) {
        if (input[i] == searched) {
            result.push_back(i);
        }
    }

    return result;
}

int main(int argc, char *argv[]) {
    std::vector<std::string> greetings;
    greetings.push_back("hello");
    greetings.push_back("hi");
    greetings.push_back("bye");
    greetings.push_back("hi");
    greetings.push_back("hello");
    greetings.push_back("bye");

    std::vector<int> indexes = getIndexes(greetings, "hi");

    for (int i = 0; i < indexes.size(); i++) {
        std::cout << indexes[i] << std::endl;
    }

    return 0;
}

Upvotes: 4

mattnewport
mattnewport

Reputation: 14057

Your main problem is that you're not initializing your result pointer to a valid array. Really though you should return a vector of indices rather than a pointer, this way the caller knows the size and doesn't have to manage the memory manually. Something like this:

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <iterator>

using namespace std;

vector<int> getIndicesOfString(const vector<string>& in, const string& check) {
    vector<int> ret;
    for (auto it = cbegin(in); it != cend(in); ++it) {
        if (*it == check) ret.push_back(distance(cbegin(in), it));
    }
    return ret;
}

int main() {
    auto v = vector<string>{"red", "orange", "yellow", "green", "blue", "indigo", "violet", "red"};
    auto indices = getIndicesOfString(v, "red");
    copy(cbegin(indices), cend(indices), ostream_iterator<int>(cout, ", "));
}

Upvotes: 1

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