C#•17mo ago

❔ DllImport From C Library

I have compiled a C library to a DLL and am trying to use some of the functions from this library in a C# project. C#:

        const string nativeLibName = "FontCache";

        [DllImport(nativeLibName, EntryPoint = "FC_CreateFont", CallingConvention = CallingConvention.Cdecl)]
        static extern unsafe IntPtr INTERNAL_FC_CreateFont();

        [DllImport(nativeLibName, EntryPoint = "FC_LoadFont")]
        static extern unsafe int INTERNAL_FC_LoadFont(
            IntPtr font, 
            IntPtr renderer,
            byte* filename_ttf,
            int pointSize,
            SDL_Color color,
            int style
        );

        const string nativeLibName = "FontCache";

        [DllImport(nativeLibName, EntryPoint = "FC_CreateFont", CallingConvention = CallingConvention.Cdecl)]
        static extern unsafe IntPtr INTERNAL_FC_CreateFont();

        [DllImport(nativeLibName, EntryPoint = "FC_LoadFont")]
        static extern unsafe int INTERNAL_FC_LoadFont(
            IntPtr font, 
            IntPtr renderer,
            byte* filename_ttf,
            int pointSize,
            SDL_Color color,
            int style
        );

FC_Font* FC_CreateFont(void);

Uint8 FC_LoadFont(FC_Font* font, SDL_Renderer* renderer, const char* filename_ttf, Uint32 pointSize, SDL_Color color, int style);

FC_Font* FC_CreateFont(void);

Uint8 FC_LoadFont(FC_Font* font, SDL_Renderer* renderer, const char* filename_ttf, Uint32 pointSize, SDL_Color color, int style);

This exception occurs when either of the above functions are called:

An unhandled exception of type 'System.EntryPointNotFoundException' occurred in Xylem-Media.dll: 'Unable to find an entry point named 'FC_CreateFont' in DLL 'FontCache'.'

An unhandled exception of type 'System.EntryPointNotFoundException' occurred in Xylem-Media.dll: 'Unable to find an entry point named 'FC_CreateFont' in DLL 'FontCache'.'

I don't know if my DllImport signatures are correct, or if there is a problem with the way I have compiled the C library - I have tried using dumpbin and various DLL explorer tools to see which symbols are available but nothing ever appears under the module I am targeting.

9 Replies

Anchy•17mo ago

https://learn.microsoft.com/en-us/cpp/build/exporting-from-a-dll-using-declspec-dllexport?view=msvc-170

Exporting from a DLL Using __declspec(dllexport)

Learn more about: Exporting from a DLL Using __declspec(dllexport)

exokemOP•17mo ago

the library is pure C I have a wrapper for SDL that works the same way without needing this syntax and adding in the __declspec(dllexport) syntax causes the project not to build

Jester•17mo ago

extern "C"
{
__declspec(dllexport) int __stdcall Example();
}

extern "C"
{
__declspec(dllexport) int __stdcall Example();
}

exokemOP•17mo ago

that syntax is cpp the library is a single C .h file

Jester•17mo ago

<:PES_SadShrug:646092743378206760> thats what i do

exokemOP•17mo ago

it works in C headers? I just don't understand why anything is needed if it is just a C library I thought the point of headers was to expose functions

Jester•17mo ago

i dont know much about it myself but i just know how to write a simple c/c++ dll for my c#

exokemOP•17mo ago

you are definitely right, after some more reading it looks like the __declspec is required because I am not just compiling c, I am compiling c to a DLL and windows always needs extra steps the only point of confusion for me now is why I get a ton of unresolved reference external symbol errors as soon as I mark any symbols to be exported I have determined that this error was because I didn't add the export flag to all symbols

Accord•17mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ DllImport From C Library