[next] [prev] [prev-tail] [tail] [up]

12.7 The @ operator

The address operator @ returns the address of a variable, procedure or function. It is used as follows:

_________________________________________________________________________________________________________
Address factor

--addressfactor- @ ------variable reference---------------------------- ---procedure identifier---| -qualfuifinecdt mioent ihdoendtifiideerntifier-|
___________________________________________________________________

The @ operator returns a typed pointer if the $T switch is on. If the $T switch is off then the address operator returns an untyped pointer, which is assignment compatible with all pointer types. The type of the pointer is ^T, where T is the type of the variable reference. For example, the following will compile

Program tcast;  
{$T-} { @ returns untyped pointer }  
 
Type art = Array[1..100] of byte;  
Var Buffer : longint;  
    PLargeBuffer : ^art;  
 
begin  
 PLargeBuffer := @Buffer;  
end.

Changing the {$T-} to {$T+} will prevent the compiler from compiling this. It will give a type mismatch error.

By default, the address operator returns an untyped pointer: applying the address operator to a function, method, or procedure identifier will give a pointer to the entry point of that function. The result is an untyped pointer.

This means that the following will work:

Procedure MyProc;  
 
begin  
end;  
 
Var  
  P : PChar;  
 
begin  
  P:=@MyProc;  
end;

By default, the address operator must be used if a value must be assigned to a procedural type variable. This behavior can be avoided by using the -Mtp or -MDelphi switches, which result in a more compatible Delphi or Turbo Pascal syntax.

[next] [prev] [prev-tail] [front] [up]