C++ Cookbook

6.3. Copying a vector

Problem

You need to copy the contents of one vector into another.

Solution

There are a couple of ways to do this. You can use a copy constructor when you create a vector, or you can use the assign member function. Example 6-3 shows how to do both.

Example 6-3. Copying vector contents

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

using namespace std;

// Util function for printing vector contents
template<typename T>
void vecPrint (const vector<T>& vec) {
   cout << "{";
   for (typename vector<T>::const_iterator p = vec.begin();
       p != vec.end(); ++p) {
      cout << "{" << *p << "} ";
   }
   cout << "}" << endl;
}

int main() {

   vector<string> vec(5);
   string foo[] = {"My", "way", "or", "the", "highway"};

   vec[0] = "Today";
   vec[1] = "is";
   vec[2] = "a";
   vec[3] = "new";
   vec[4] = "day";

   vector<string> vec2(vec);
   vecPrint(vec2);

   vec.at(0) = "Tomorrow";

   vec2.assign(vec.begin(), vec.end()); // Copy each element over
   vecPrint(vec2);                      // with assign
   
   vec2.assign(&foo[0], &foo[5]); // Assign works for anything that
   vecPrint(vec2);                // behaves like an iterator

   vector<string>::iterator p;

   p = find(vec.begin(), vec.end(), "new");

   vec2.assign(vec.begin(), p); // Copy a subset of the full range
   vecPrint(vec2);              // of vec
}

Discussion

Copying a vector is easy; there are two ways to do it. You can copy construct one vector from another, just like any other object, or you can use the assign member function. There is little to say about the copy constructor; just pass in the ...