{"id":1609,"date":"2018-11-12T08:38:59","date_gmt":"2018-11-12T13:38:59","guid":{"rendered":"http:\/\/codinggorilla.domemtech.com\/?p=1609"},"modified":"2018-11-26T13:09:11","modified_gmt":"2018-11-26T18:09:11","slug":"re-inventing-the-p-invoke-generator","status":"publish","type":"post","link":"http:\/\/165.227.223.229\/index.php\/2018\/11\/12\/re-inventing-the-p-invoke-generator\/","title":{"rendered":"Re-inventing the p\/invoke generator"},"content":{"rendered":"

If you’ve been programming in C# for a while, at some point you found yourself needing to call C libraries. It isn’t often, but when you have to do it, it’s like pulling teeth. One option is to set up a C++\/CLI interface; the other is a p\/invoke interface to a DLL containing the C code. It’s relatively easy to set up a p\/invoke interface<\/a> in your C# code for the C code, which you export with a DLL–if you only need to call a few C functions. But, if the API is large, you stare at the code for a while,\u00c2\u00a0deciding whether it is really worth writing out all the declarations you need to make the\u00c2\u00a0calls. Many people throw caution to the wind, write packages for large, popular C APIs so you don’t have to, which you can find on the Nuget website. One example is ManagedCuda<\/a>, an API for CUDA programming from C#. Unfortunately, people get tired of trying to keep these packages up to date, and so these packages become obsolete. Another approach is through automatic means, whereby a tool reads the C++ headers (or DLL) and output the decls you call. A p\/invoke generator<\/a>\u00c2\u00a0reads C header files and outputs C# code with the p\/invoke declarations that you can include in your code. These tools sometimes work, but often they don’t.<\/p>\n

This blog entry is a “heads up” note about my thoughts for a new type of p\/invoke generator.<\/p>\n

Existing p\/invoke generators<\/h2>\n

SWIG<\/a> is one of several p\/invoke generators. It reads C header files\u00c2\u00a0and generates code that you can add to your program. To use SWIG, you need to specify what functions to\u00c2\u00a0generate, and how to map data types between C# and C. Unfortunately,\u00c2\u00a0it doesn’t help much if the API you are trying to call changes often, forcing you to re-learn how to use SWIG’s\u00c2\u00a0byzantine\u00c2\u00a0rules. Alternatives to SWIG are CppSharp<\/a> and ClangSharp<\/a>. These tools use Clang<\/a> and hardcode AST visitor code<\/a> to output finely tuned C# code. But, they aren’t extensible, and they also often get confused whether a function parameter is “in” or “out” or “ref”. Some of these tools are no longer available, adding to the “fun”.<\/p>\n

SWIG<\/h4>\n