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How to: Expose an STL/CLR Container from an Assembly

STL/CLR containers such as list and map are implemented as template ref classes. Because C++ templates are instantiated at compile time, two template classes that have exactly the same signature but are in different assemblies are actually different types. This means that template classes cannot be used across assembly boundaries.

To make cross-assembly sharing possible, STL/CLR containers implement the generic interface ICollection<T>. By using this generic interface, all languages that support generics, including C++, C#, and Visual Basic, can access STL/CLR containers.

This topic shows you how to display the elements of several STL/CLR containers written in a C++ assembly named StlClrClassLibrary. We show two assemblies to access StlClrClassLibrary. The first assembly is written in C++, and the second in C#.

If both assemblies are written in C++, you can access the generic interface of a container by using its generic_container typedef. For example, if you have a container of type cliext::vector<int>, then its generic interface is: cliext::vector<int>::generic_container. Similarly, you can get an iterator over the generic interface by using the generic_iterator typedef, as in: cliext::vector<int>::generic_iterator.

Since these typedefs are declared in C++ header files, assemblies written in other languages cannot use them. Therefore, to access the generic interface for cliext::vector<int> in C# or any other .NET language, use System.Collections.Generic.ICollection<int>. To iterate over this collection, use a foreach loop.

The following table lists the generic interface that each STL/CLR container implements:

STL/CLR container

Generic interface

deque<T>

ICollection<T>

hash_map<K, V>

IDictionary<K, V>

hash_multimap<K, V>

IDictionary<K, V>

hash_multiset<T>

ICollection<T>

hash_set<T>

ICollection<T>

list<T>

ICollection<T>

map<K, V>

IDictionary<K, V>

multimap<K, V>

IDictionary<K, V>

multiset<T>

ICollection<T>

set<T>

ICollection<T>

vector<T>

ICollection<T>

NoteNote

Because the queue, priority_queue, and stack containers do not support iterators, they do not implement generic interfaces and cannot be accessed cross-assembly.

Description

In this example, we declare a C++ class that contains private STL/CLR member data. We then declare public methods to grant access to the private collections of the class. We do it in two different ways, one for C++ clients and one for other .NET clients.

Code

// StlClrClassLibrary.h
#pragma once

#include <cliext/deque>
#include <cliext/list>
#include <cliext/map>
#include <cliext/set>
#include <cliext/stack>
#include <cliext/vector>

using namespace System;
using namespace System::Collections::Generic;
using namespace cliext;

namespace StlClrClassLibrary {

    public ref class StlClrClass
    {
    public:
        StlClrClass();

        // These methods can be called by a C++ class
        // in another assembly to get access to the
        // private STL/CLR types defined below.
        deque<wchar_t>::generic_container ^GetDequeCpp();
        list<float>::generic_container ^GetListCpp();
        map<int, String ^>::generic_container ^GetMapCpp();
        set<double>::generic_container ^GetSetCpp();
        vector<int>::generic_container ^GetVectorCpp();

        // These methods can be called by a non-C++ class
        // in another assembly to get access to the
        // private STL/CLR types defined below.
        ICollection<wchar_t> ^GetDequeCs();
        ICollection<float> ^GetListCs();
        IDictionary<int, String ^> ^GetMapCs();
        ICollection<double> ^GetSetCs();
        ICollection<int> ^GetVectorCs();

    private:
        deque<wchar_t> ^aDeque;
        list<float> ^aList;
        map<int, String ^> ^aMap;
        set<double> ^aSet;
        vector<int> ^aVector;
    };
}

Description

In this example, we implement the class declared in Example 1. In order for clients to use this class library, we use the manifest tool mt.exe to embed the manifest file into the DLL. For details, see the code comments.

For more information on the manifest tool and side-by-side assemblies, see Building C/C++ Isolated Applications and Side-by-side Assemblies.

Code

// StlClrClassLibrary.cpp
// compile with: /clr /LD /link /manifest
// post-build command: (attrib -r StlClrClassLibrary.dll & mt /manifest StlClrClassLibrary.dll.manifest /outputresource:StlClrClassLibrary.dll;#2 & attrib +r StlClrClassLibrary.dll)

#include "StlClrClassLibrary.h"

namespace StlClrClassLibrary
{
    StlClrClass::StlClrClass()
    {
        aDeque = gcnew deque<wchar_t>();
        aDeque->push_back(L'a');
        aDeque->push_back(L'b');

        aList = gcnew list<float>();
        aList->push_back(3.14159f);
        aList->push_back(2.71828f);

        aMap = gcnew map<int, String ^>();
        aMap[0] = "Hello";
        aMap[1] = "World";

        aSet = gcnew set<double>();
        aSet->insert(3.14159);
        aSet->insert(2.71828);

        aVector = gcnew vector<int>();
        aVector->push_back(10);
        aVector->push_back(20);
    }

    deque<wchar_t>::generic_container ^StlClrClass::GetDequeCpp()
    {
        return aDeque;
    }

    list<float>::generic_container ^StlClrClass::GetListCpp()
    {
        return aList;
    }

    map<int, String ^>::generic_container ^StlClrClass::GetMapCpp()
    {
        return aMap;
    }

    set<double>::generic_container ^StlClrClass::GetSetCpp()
    {
        return aSet;
    }

    vector<int>::generic_container ^StlClrClass::GetVectorCpp()
    {
        return aVector;
    }

    ICollection<wchar_t> ^StlClrClass::GetDequeCs()
    {
        return aDeque;
    }

    ICollection<float> ^StlClrClass::GetListCs()
    {
        return aList;
    }

    IDictionary<int, String ^> ^StlClrClass::GetMapCs()
    {
        return aMap;
    }

    ICollection<double> ^StlClrClass::GetSetCs()
    {
        return aSet;
    }

    ICollection<int> ^StlClrClass::GetVectorCs()
    {
        return aVector;
    }
}

Description

In this example, we create a C++ client that uses the class library created in Examples 1 and 2. This client uses the generic_container typedefs of the STL/CLR containers to iterate over the containers and to display their contents.

Code

// CppConsoleApp.cpp
// compile with: /clr /FUStlClrClassLibrary.dll

#include <cliext/deque>
#include <cliext/list>
#include <cliext/map>
#include <cliext/set>
#include <cliext/vector>

using namespace System;
using namespace StlClrClassLibrary;
using namespace cliext;

int main(array<System::String ^> ^args)
{
    StlClrClass theClass;

    Console::WriteLine("cliext::deque contents:");
    deque<wchar_t>::generic_container ^aDeque = theClass.GetDequeCpp();
    for each (wchar_t wc in aDeque)
    {
        Console::WriteLine(wc);
    }
    Console::WriteLine();

    Console::WriteLine("cliext::list contents:");
    list<float>::generic_container ^aList = theClass.GetListCpp();
    for each (float f in aList)
    {
        Console::WriteLine(f);
    }
    Console::WriteLine();

    Console::WriteLine("cliext::map contents:");
    map<int, String ^>::generic_container ^aMap = theClass.GetMapCpp();
    for each (map<int, String ^>::value_type rp in aMap)
    {
        Console::WriteLine("{0} {1}", rp->first, rp->second);
    }
    Console::WriteLine();

    Console::WriteLine("cliext::set contents:");
    set<double>::generic_container ^aSet = theClass.GetSetCpp();
    for each (double d in aSet)
    {
        Console::WriteLine(d);
    }
    Console::WriteLine();

    Console::WriteLine("cliext::vector contents:");
    vector<int>::generic_container ^aVector = theClass.GetVectorCpp();
    for each (int i in aVector)
    {
        Console::WriteLine(i);
    }
    Console::WriteLine();

    return 0;
}

Output

cliext::deque contents:
a
b

cliext::list contents:
3.14159
2.71828

cliext::map contents:
0 Hello
1 World

cliext::set contents:
2.71828
3.14159

cliext::vector contents:
10
20

Description

In this example, we create a C# client that uses the class library created in Examples 1 and 2. This client uses the ICollection<T> methods of the STL/CLR containers to iterate over the containers and to display their contents.

Code

// CsConsoleApp.cs
// compile with: /r:Microsoft.VisualC.STLCLR.dll /r:StlClrClassLibrary.dll /r:System.dll

using System;
using System.Collections.Generic;
using StlClrClassLibrary;
using cliext;

namespace CsConsoleApp
{
    class Program
    {
        static int Main(string[] args)
        {
            StlClrClass theClass = new StlClrClass();

            Console.WriteLine("cliext::deque contents:");
            ICollection<char> iCollChar = theClass.GetDequeCs();
            foreach (char c in iCollChar)
            {
                Console.WriteLine(c);
            }
            Console.WriteLine();

            Console.WriteLine("cliext::list contents:");
            ICollection<float> iCollFloat = theClass.GetListCs();
            foreach (float f in iCollFloat)
            {
                Console.WriteLine(f);
            }
            Console.WriteLine();

            Console.WriteLine("cliext::map contents:");
            IDictionary<int, string> iDict = theClass.GetMapCs();
            foreach (KeyValuePair<int, string> kvp in iDict)
            {
                Console.WriteLine("{0} {1}", kvp.Key, kvp.Value);
            }
            Console.WriteLine();

            Console.WriteLine("cliext::set contents:");
            ICollection<double> iCollDouble = theClass.GetSetCs();
            foreach (double d in iCollDouble)
            {
                Console.WriteLine(d);
            }
            Console.WriteLine();

            Console.WriteLine("cliext::vector contents:");
            ICollection<int> iCollInt = theClass.GetVectorCs();
            foreach (int i in iCollInt)
            {
                Console.WriteLine(i);
            }
            Console.WriteLine();

            return 0;
        }
    }
}

Output

cliext::deque contents:
a
b

cliext::list contents:
3.14159
2.71828

cliext::map contents:
0 Hello
1 World

cliext::set contents:
2.71828
3.14159

cliext::vector contents:
10
20

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