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c++stringuwpwindows-runtimecode-reuse

UWP - Suggested way for reusing string parsing functions across WinRT modules

I have a number of C++ projects in my solution that were written by other teams before I started working on my UWP app, and all of these projects use std::strings. So, to ease the communication between the other projects and my WinRT modules, I wrote some string conversion functions to go from std::strings to Platform::Strings and vice versa.

I'm in the process of converting my UWP codebase into WinRT modules and I'm coming across a recurring problem: because WinRT modules don't allow you to have classes or functions with public native types, I am unable to have my string functions publicly accessible. A private, protected, or internal declaration is fine for passing around native types, just not public.

Many of my modules need to communicate down into the native C++ code and I don't want to have to redefine my string functions again and again for each individual file that needs a std::string.

Is there anything I can do so I can reuse my string functions across WinRT modules? Has anyone else had a similar problem? Any suggestions are greatly appreciated! Thank you

Solution

  • You have two options.

    1. Make those functions inline, and define all of them in a header file. Then, include the header file everywhere you want to consume them. This is a more straightforward solution without requiring you to mess with your build system.

    2. You can compile those functions into one of your DLLs, and import them to other ones. Let's call the DLL where you put your functions in "StringModule.dll". You'll need to put those functions in a .cpp/.h header file pair, then compile that .cpp file into StringModule.dll. Then, annotate your functions with a define that evaluates to __declspec(dllexport) when building StringModule.dll, and __declspec(dllimport) when building all the other DLLs. For instance:

      #ifndef BUILDING_STRING_CONVERSIONS_DLL // This should be defined to 1 when building StringModule.dll
#define BUILDING_STRING_CONVERSIONS_DLL 0
#endif

#if BUILDING_STRING_CONVERSIONS_DLL
#define MY_STRING_API __declspec(dllexport)
#else
#define MY_STRING_API __declspec(dllimport)
#endif

namespace MyStringFunctions
{
    MY_STRING_API Platform::String^ ConvertStdStringToPlatformString(const std::string& str);
    MY_STRING_API std::string ConvertPlatformStringToStdString(Platform::String^ str);
}

    When you build StringModule.dll, there will be StringModule.lib file created next to it. You'll have to pass its path to the linker as an argument when building all the DLLs that consume your string functions. In all the places where you want to use your DLL, just include that header file and use them as usual.