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7.1.2 Declaring external variables

Some libaries or code blocks have variables which they export. You can access these variables much in the same way as external functions. To access an external variable, you declare it as follows:

Var  
  MyVar : MyType; external name 'varname';

The eect of this declaration is twofold:

  1. No space is allocated for this variable.
  2. The name of the variable used in the assembler code is varname. This is a case sensitive name, so you must be careful.

The variable will be accessible with it's declared name, i.e. MyVar in this case.

A second possibility is the declaration:

Var  
  varname : MyType; cvar; external;

The eect of this declaration is twofold as in the previous case:

  1. The external modier ensures that no space is allocated for this variable.
  2. The cvar modier tells the compiler that the name of the variable used in the assembler code is exactly as specied in the declaration. This is a case sensitive name, so you must be careful.

The rst possibility allows you to change the name of the external variable for internal use.

As an example, let's look at the following C le (in extvar.c):

/*  
Declare a variable, allocate storage  
*/  
int extvar = 12;

And the following program (in extdemo.pp):

Program ExtDemo;  
 
{$L extvar.o}  
 
Var { Case sensitive declaration !! }  
    extvar : longint; cvar;external;  
    I : longint; external name 'extvar';  
begin  
  { Extvar can be used case insensitive !! }  
  Writeln ('Variable ''extvar'' has value: ',ExtVar);  
  Writeln ('Variable ''I''      has value: ',i);  
end.

Compiling the C le, and the pascal program:

gcc -c -o extvar.o extvar.c  
ppc386 -Sv extdemo

Will produce a program extdemo which will print

Variable 'extvar' has value: 12  
Variable 'I'      has value: 12

on your screen.

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