BlitzMax/Language/Interfacing with C

You can use the Import command to add certain non-BlitzMax source files to your projects, and the Extern command to make the functions in those files available to BlitzMax applications.

The currently supported non-BlitzMax source file types are: .c (C); .cpp (C++); .cxx (C++); .m (ObjectiveC); and .s (Assembler).

BlitzMax will use the GNU compiler tools to compile C, C++ and ObjectiveC files, and either the 'fasm' assembler for x86 assembly or GNU assembler for PowerPC assembly.

Here is a simple example of importing C source code into your project and accessing a C function:

//- file: c_funcs.c - int Doubler( int x ){ return x+x; }

'- file: app.bmx - Import "c_funcs.c"

Extern Function Doubler( x ) End Extern

Print Doubler(10)

You can also use Import to add a C compiler 'include' directory. To do this, use an import path that ends in "*.h", for example:

Import "include/*.h"

Extern can also be used to work with C++ style objects from within BlitzMax. To do this, simply place a user-defined type declaration within an extern block. For example:

//- file: mytype.cpp -
 * 1) include

class MyType{ public: virtual ~MyType{} virtual void Test{ printf( "Hello World!\n" ); } };

extern "C"{

MyType *CreateMyType{ return new MyType; }

void DestroyMyType( MyType *t ){ delete t; }

'- File: app.bmx - Import "mytype.cpp"

Extern

Type TMyType Method _pad1 'padding for virtual destructors method _pad2 Method Test End Type

Function CreateMyType:TMyType Function DestroyMyType( t:TMyType )

End Extern

Local t:TMyType=CreateMyType t.Test DestroyMyType t

Note that there are several limits on the use of extern types:


 * Methods declared in an extern type must be declared virtual in the C++ class.
 * Objects of extern type cannot be created with New. Instead, such objects must be created by an extern function.
 * Extern types can extend other extern types, but can not extend standard BlitzMax types. Similarly, BlitzMax types can not extend extern types.
 * Objects of extern type cannot be cast to 'Object'.