Follow this steps and it will work like desired:
1 - Add a reference to System.Configuration
2 - Add New Item > Visual C++ > Utility > Configuration file
3 - Open app.config and add your settings for example:
<configuration>
<appSettings>
<add key="greeting" value="Hallo world!" />
</appSettings>
</configuration>
4 - Copy the app.config to the output folder in the post build event: goto Project Properties > Configuration Properties > Build Events > Post-Build Events > Command Line and add this:
copy app.config "$(TargetPath).config"
5 - Read your settings:
String^ greeting = ConfigurationManager::AppSettings["greeting"];
Console::WriteLine(greeting);
Here's an AppConfigDemo project in C++/CLI.