Global variables

A variable is global if it is exported from a module. This usually refers to variables declared in a var section

• prior any other nested block in a program, or
• in the interface part of a unit.

Global variables can be accessed from all other modules that import the exporting modules. Note, however, that a program can not be imported.

program globalVariableDemo(input, output, stdErr);
var
    x: integer;

procedure doMagic;
begin
    // here, x is global to doMagic
end;

procedure foo;
var
    // shadow the global x
    x: integer;
begin
    // here, x is local,
    // as the top-scope x can not be accessed
end;

// MAIN //
begin
    // here, x is local
end.

remarks

If speed matters, global variables are/were used for frequently invoked routines, since allocating local variables on the stack takes time. This, however, is considered bad style. Nest your variables as deep as possible, but as high as necessary.

A resourceString variable is always global.

The FPC supports thread variables, too. They are sort of half-way between global and local variables. A threadVar variable is local to a thread.

see also

• Tutorial: Scope
• singleton pattern
• Article “Global variable” on the English Wikipedia

From the Free Pascal wiki, page "Global variables", as it stood on 2024-02-21 after a change by Elender, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's Licensing page. If you have concerns about this material, message the admin.