Thiscall

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__Thiscall

Specifies the Thiscall calling convention in a procedure declaration

Syntax

declare Sub name __Thiscall [Overload] [Alias "alias"] ( parameters )
declare Function name __Thiscall [Overload] [Alias "alias"] ( parameters ) [ ByRef ] As return_type
Sub name [__Thiscall] [Overload] [Alias "alias"] ( parameters )
Function name [__Thiscall] [Overload] [Alias "alias"] ( parameters ) [ ByRef ] As return_type

Description

Thiscall is a calling convention for x86 targets where the first integral argument is passed in the ECX register instead of on the stack. All other arguments are passed right to left and callee cleans up the stack (like Stdcall).

On win32 x86, mingw+gcc will use Thiscall as the default calling convention for non-static member procedures in classes passing the hidden This parameter by ECX register instead of pushing to the stack.

Default calling convention on win32 x86 inside an extern "c++" block for non-static member procedures is Thiscall.

Thiscall can be explicitly specified for normal procedures and static member procedures to override the default calling convention.
Other calling conventions (Cdecl/Stdcall/etc) can be explicitly specified to override the default Thiscall calling convention on non-static member procedures.

Thiscall can be specified at both the declaration and the definition.
If a procedure definition has a declaration (with calling convention explicit or by default) and the definition does not explicitly specify a calling convention, then the calling convention is implied by the declaration.

Remarks

Differences from QB

• New to FreeBASIC

See also

• cdecl, stdcall, Fastcall
• Declare
• Sub, Function

Examples

- If inside extern "c++" and also on win32 / x86, and it's a non-static member procedure, and no other calling convention is given, the default is __thiscall:

Extern "c++"

    Type T Extends Object

        Declare Constructor() '' __thiscall is default

    End Type

    Constructor T()  '' __thiscall is default

    End Constructor

End Extern

- If definition is outside the extern "c++" block, then __thiscall is optional on the definition (if the default for the non-static member procedure was __thiscall):

Extern "c++"

    Type T Extends Object

        Declare Constructor() '' __thiscall is default

    End Type

End Extern

Constructor T() '' __thiscall is implied by declaration

End Constructor

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Category: Procedures
Kind: function

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