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Iterating Over STL Collection By Using for each

The for each keyword can be used to iterate over a Standard C++ Library (STL) collection.

Remarks

An STL collection is also known as a container. For more information, see STL Containers.

Example

The following code example uses for each to iterate over a <map>.

// for_each_stl.cpp
// compile with: /EHsc
#include <map>
#include <iostream>
#include <string>
using namespace std;

int main() {
   int retval  = 0;
   map<string, int> months;

   months["january"] = 31;
   months["february"] = 28;
   months["march"] = 31;
   months["april"] = 30;
   months["may"] = 31;
   months["june"] = 30;
   months["july"] = 31;
   months["august"] = 31;
   months["september"] = 30;
   months["october"] = 31;
   months["november"] = 30;
   months["december"] = 31;

   map<string, int> months_30;

   for each( pair<string, int> c in months )
      if ( c.second == 30 )
         months_30[c.first] = c.second;

   for each( pair<string, int> c in months_30 )
      retval++;

   cout << "Months with 30 days = " << retval << endl;
}

Output

Months with 30 days = 4

Example

The following code example uses a const reference (const&) for an iteration variable with STL containers. You can use a reference (&) as an iteration variable on any collection of a type that can be declared as a T&.

// for_each_stl_2.cpp
// compile with: /EHsc
#include <vector>
#include <iostream>
using namespace std;

int main() {
   int retval = 0;
      
   vector<int> col(3);
   col[0] = 10;
   col[1] = 20;
   col[2] = 30;
   
   for each( const int& c in col )
      retval += c;

   cout << "retval: " << retval << endl;
}

Output

retval: 60

Remarks

There are no platform-specific remarks about this feature.

Compiler option: /ZW

Remarks

There are no platform-specific remarks about this feature.

Compiler option: /clr

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