CppSharp/Manual.md

Clang/.NET code generation tool User's Manual

1. Introduction ===============

What does it do?

This tool allows you to generate .NET bindings that wrap C/C++ code allowing interoperability with managed languages. This can be useful if you have an existing native codebase and want to add scripting support, or want to consume an existing native library in your managed code.

Why reinvent the wheel?

There are not many automated binding tools around, the only real alternative is SWIG. So how is it different from SWIG?

• No need to generate a C layer to interop with C++.
• Based on an actual C++ parser (Clang) so very accurate.
• Understands C++ at the ABI (application binary interface) level
• Easily extensible semantics via user passes
• Strongly-typed customization APIs
• Can be used as a library

2. Supported C/C++ language features ====================================

In this section we will go through how the generator deals with each C / C++ feature.

C/C++ Types

Fundamental types

These are mapped to .NET types as follows:

1. Integral types

char -> System::Byte bool -> System::Boolean short -> System::Int16 int, long -> System::Int32 long long -> System::Int64

Signedness is also preserved in the conversions.

2. Floating-point types

float -> System::Single double -> System::Double

3. Other types

wchar_t -> System::Char void -> System::Void

Derived types

1. Arrays

These are mapped to .NET CLR arrays.

2. Function Pointers / Pointers to Members

These are mapped to .NET CLR delegates.

3. Pointers

These are mapped to .NET CLR references unless:

void* -> System::IntPtr const char* -> System::String

4. References

References are mapped to .NET CLR references just like pointers.

Typedefs

We do not preserve type definitions since .NET and its main language C# do not have the concept of type aliases like C/C++. There is an exception in the case of a typedef'd function (pointer) declaration. In this case generate a .NET delegate with the name of the typedef.

Enums

C/C++ enums are translated automatically to .NET enumerations.

Special cases to be aware of:

1. Anonymous enums

C and C++ enums (this does not apply to the new C++11 strongly typed enums) do not introduce their own scope. This means the enumerated values will leak into an outer context, like a class or a namespace. When this is detected, the generator tries to map to an outer enclosing context and generate a new name.

2. Flags / Bitfields

Some enumerations represent bitfield patterns. The generator tries to check for this with some heuristics. If there are enough values in the enum to make a good guess, we apply the [Flags] .NET attribute to the wrapper enum.

Functions

Since global scope functions are not supported in C# (though they are available in the CLR) they are mapped as a static function in a class, to be consumable by any CLS-compliant language.

By default all globals functions of a translation unit are mapped to a static class with the name of of the unit prefixed by the namespace.

Special cases to be aware of:

1. Variadic arguments (TODO)

C/C++ variadic arguments need careful handling because they are not contrained to be of the same type.

.NET provides two types of variadic arguments support:

• C# params-style

This is the preferred and idiomatic method but can only be used when we know the variadic arguments will all be of the same type. Since we have no way to derive this fact from the information in C/C++ function signatures, you will need set this explicitly.

• Argslist

This is a lesser known method for variadic arguments in .NET and was added by Microsoft for better C++ compatibility in the runtime. As you can guess, this does support different types per variable argument but is more verbose and less idiomatic to use. By default we use this to wrap variadic functions.

2. Default arguments

We do not try to wrap arguments default values yet. This is desired but needs more research since potentially all C++ constant expressions can be used as default arguments, though it would be pretty simple to add this for the common case of null constants.

Classes / Structs

Unlike .NET, in which there is an explicit differentiation of the allocation semantics of the type in the form of classes (reference types) and structs (value types), in C++ both classes and structs are identical and can be used in both heap (malloc/new) and automatic (stack) allocations.

By default, classes and structs are wrapped as .NET reference types. If your type is supposed to be a value type, then you can instruct the generator to issue a .NET value type. You should use value types if the types are cheap to construct and/or if you creating a lot of instances.

POD (Plain Old Data)

TODO: If the native type is a POD type, that means we can safely convert it to a value type. This would make the generator do the right thing by default and is pretty easy to implement.

Constructors

Constructors are mapped to .NET class constructors.

Note: An extra constructor is generated that takes a native pointer to the class. This allows construction of managed instances from native instances.

Destructors

TODO: Destructors need to be mapped to the Dispose() pattern of .NET.

Overloaded Operators

Most of the regular C++ operators can be mapped to .NET operator overloads.

TODO: In case we get unsupported C++ operators then we should emit a warning, and introduce a new automatically named method to represent the operator. The user should then explicitly give a name to the operator to get rid of the warning.

Conversion Operators

TODO: Convert C++ conversion operators to .NET conversion operators.

Inheritance

C++ supports different types of implementation inheritance:

1. Single inheritance

This is the simplest case

2. Multiple inheritance

3. Virtual inheritance

This is not supported for now.

Bitfields

This feature is not supported yet.

Unions

This feature is not supported yet.

Templates

Template types are supported at the moment

At the moment, template specializations are not exported yet.

Preprocessor defines

Since C preprocessor definitions can be used for very different purposes, we can only do so much when converting them to managed code.

1. Numeric defines

These can be translated to proper .NET enumerations.

2. String defines

These can be translated to .NET static constant definitions.

3. Generalized expressions

This case is not supported and probably never will.

4. Function-like macros

This case is not supported and probably never will.

Comments

Doxygen-style C++ comments are translated to .NET XML-style comments. This feature is experimental and limited to what Doxygen directives the upstream Clang parser supports.

3. Customization ================

The generator provides various ways to customize the generation process.

Type Maps

If all you need to do is customize what gets generated for a type, then you can use the type maps feature. This lets you hook into the process for a specific type pattern.

Standard library support

The generator provides type maps for the most common C/C++ standard library types:

• String

• Containers

1. Vector

2. Map

3. Set

Passes

If you need more control then you can write your own pass. Passes have full access to the parsed AST (Abstract Syntax Tree) so you can modify the entire structure and declaration data of the source code. This is very powerful and should allow you to pretty much do anything you want.

The generator already provides many ready-to-use passes that can transform the wrapped code to be more idiomatic:

Renaming passes

Use these to rename your declarations automatically so they follow .NET conventions. When setting up renaming passes, you can declare what kind of declarations they apply to. There are two different kinds of rename passes:

1. Case renaming pass

This is a very simple to use pass that changes the case of the name of the declarations it matches.

2. Regex renaming pass

This pass allows you to do powerful regex-based pattern matching renaming of declaration names.

Function to instance method

This pass introduces instance methods that call a C/C++ global function. This can be useful to map "object-oriented" design in C to .NET classes. If your function takes an instance to a class type as the first argument, then you can use this pass.

Function to static method pass

This pass introduces static methods that call a C/C++ global function. This can be useful to gather related global functions inside the object it belongs to semantically.

Getter/setter to property pass

This pass introduces a property that calls the native C/C++ getter and setter function. This can make the API much more idiomatic and easier to use under .NET languages.

Internal passes

Some internal functionalities are also implemented as passes like checking for invalid declaration names or resolving incomplete declarations. Please check the developer manual for more information about these.

4. Targets ==========

The backend of the generator is abstracted and it can target different .NET binding technologies:

1. C++/CLI

2. C# (P/Invoke)

3. Command Line Reference =========================

When you launch the executable with no options, you are presented with the following options:

Usage: Generator.exe [options]+ headers
Generates .NET bindings from C/C++ header files.

Options:
  -D, --defines=VALUE
  -I, --include=VALUE
      --ns, --namespace=VALUE

  -o, --outdir=VALUE
      --debug
      --lib, --library=VALUE
  -t, --template=VALUE
  -a, --assembly=VALUE
  -v, --verbose
  -h, -?, --help

• -D: Defines preprocessor macros (equivalent to #define).

• -I: Specifies additional include directories.

• -o: Specifies the base output directory for generated files.

• -a: Specifies the .NET assembly that should be used as a driver.