1.8 Allocating and deallocating C storage

with-stack-structure

Statement macro

Summary

Allocates an object within the scope of the body of the code.

Signature

with-stack-structure (name :: wrapper-type 
                      #key element-count extra-bytes) 
  body 
end [with-stack-structure]

Arguments

name: A Dylan variable name.
wrapper-type: A Dylan name.
element-count: An instance of <integer>.
extra-bytes: An instance of <integer>.

Library

c-ffi

Module

c-ffi

Description

Allocates an object name within the scope of a body. The element-count and extra-bytes options behave as in make. The memory that was allocated is freed after body exits.

This macro gives the object dynamic extent.

? define C-struct <PointStruct>
    slot x-coord :: <C-unsigned-short>;
    slot y-coord :: <C-unsigned-short>;
    pointer-type-name: <PointStruct*>
  end C-struct;

// Defined <PointStruct>, x-coord, x-coord-setter, 
// y-coord, and y-coord-setter.

? define constant <Point> = <PointStruct*>;
// Defined <Point>.

? define C-function PlotPoint
    parameter point :: <Point>;
    c-name: "PlotPoint";
  end C-function;
// Defined PlotPoint.

? define method plot (x, y)
    with-stack-structure (point :: <Point>)
      point.x-coord := 20;
      point.y-coord := 30;
      PlotPoint(point);
    end;
  end;
// Defined plot.

? plot(20, 20);

? plot(50, 50);