'System' : a namespace with this name does not exist

Question

I had a C++ project which was running perfectly. Now I copied the project to another folder and added the project to a WPF application solution.

Now the C++ project is giving me lot of build errors. One of them is "System' : a namespace with this name does not exist".

Below are the lines which creates this error.

#include "stdafx.h"

using namespace System;
using namespace System::Reflection;
using namespace System::Runtime::CompilerServices;
using namespace System::Runtime::InteropServices;
using namespace System::Security::Permissions;

The above lines are in AssemblyInfo.cpp file. I don't have any experience of C++, so finding it difficult to remove the errors. Any help is appreciated. Below is another error which might be helpful for you to resolve the issue.

managed targeted code requires a '/clr' option

Thanks in advance.

Do you intend to write in C++ for .NET or natively? Existence of System::* shows clearly, that its a C++/CLI project (not C++/Win32). — Spook
Actually C++ is has some native code and wrapper and WPF does the UI. I know it is C++/CLI project. But why is it giving errors when added to another solution as this does not depend upon any other project. — Narendra
Check in project's preferences, whether the compiler knows, that it's a C++/CLI project, because it seems, that it doesn't :) — Spook
Project properties | Configuration properties | General | Common Language Runtime Support. If the project is a C++/CLI one, there should be Common Language Runtime Support (/clr). — Spook

Mif Mif · Accepted Answer · 2013-12-15T14:44:15

Set Common Language RunTime Support to be "Common Language RunTime Support (/clr)" in 2 places in your project properties :

For Visual Studio before 2019:

Configuration Properties -> General
Configuration Properties -> C/C++ -> General

For Visual Studio 2019:

Configuration Properties -> Advanced -> C++/CLI Properties
Configuration Properties -> C/C++ -> General

'System' : a namespace with this name does not exist

3 Answers