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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 -----
#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'.
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