Delphi function Parameters Pass default parameters (value values), VAR (pass-through), out (output), const (constant) class four

Delphi parameters can be divided into: default parameters (Value), VAR (address), out (output), const (constant) four class

You can compare the knowledge of C + + with analogy learning.

1. The default parameter is the pass value, will not be changed, example

function Myfun (x:integer): Integer;begin    Inc (x);    Result: = X;end;

The 2.var parameter is the address that will be changed, example

function Myfunvar (var x:integer): Integer;begin    Inc (x);    Result: = X;end;

3.out parameters are supported for COM, and the result of Var is the same, generally we do not need

function myfunout (out X:integer): Integer;begin    Inc (x);    Result: = X;end;

4.const parameters are absolutely not assignable, this is the way the compiler optimizes, as much as possible

function Myfunconst (const X:integer): Integer;begin    Inc (x);    This is an error because the parameter with the const prefix is the Result that cannot be modified    : = X;end;

　　

Here are the tests that call these functions

Procedure Tform1.button1click (sender:tobject); var   a:integer;begin    A: = 5;    Myfun (a);    ShowMessage (IntToStr (a));    6        A: = 6;    Myfunvar (a);    ShowMessage (IntToStr (a));    7    A: = 6;    Myfunout (a);    ShowMessage (IntToStr (a));    7    A: = 6;    Myfunconst (a);    ShowMessage (IntToStr (a));    6, because in the myfunconst is not the const parameter can be modified end;

　　

Delphi function Parameters Pass default parameters (value values), VAR (pass-through), out (output), const (constant) class four