Global variables: what changed
Revision 0 to 1. Removed lines have a minus sign; added lines have a plus sign.
Title: Global variables
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| 1 | + | A [[Variable|variable]] is global if it is exported from a module. This usually refers to variables declared in a [[Var|var section]] | |
| 2 | + | ||
| 3 | + | - prior any other nested [[Block|block]] in a [[Program|program]], or | |
| 4 | + | - in the `interface` part of a [[Unit|unit]]. | |
| 5 | + | ||
| 6 | + | Global variables can be accessed from all other modules that import the exporting modules. Note, however, that a `program` can not be imported. | |
| 7 | + | ||
| 8 | + | ``` pascal | |
| 9 | + | program globalVariableDemo(input, output, stdErr); | |
| 10 | + | var | |
| 11 | + | x: integer; | |
| 12 | + | ||
| 13 | + | procedure doMagic; | |
| 14 | + | begin | |
| 15 | + | // here, x is global to doMagic | |
| 16 | + | end; | |
| 17 | + | ||
| 18 | + | procedure foo; | |
| 19 | + | var | |
| 20 | + | // shadow the global x | |
| 21 | + | x: integer; | |
| 22 | + | begin | |
| 23 | + | // here, x is local, | |
| 24 | + | // as the top-scope x can not be accessed | |
| 25 | + | end; | |
| 26 | + | ||
| 27 | + | // MAIN // | |
| 28 | + | begin | |
| 29 | + | // here, x is local | |
| 30 | + | end. | |
| 31 | + | ``` | |
| 32 | + | ||
| 33 | + | ## remarks | |
| 34 | + | ||
| 35 | + | If speed matters, global variables are/were used for frequently invoked routines, since allocating [[Local variables|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. | |
| 36 | + | ||
| 37 | + | A [[Resourcestring|resourceString variable]] is always global. | |
| 38 | + | ||
| 39 | + | The [[FPC]] supports thread variables, too. They are sort of half-way between global and local variables. A [[ThreadVar|threadVar variable]] is local to a thread. | |
| 40 | + | ||
| 41 | + | ## see also | |
| 42 | + | ||
| 43 | + | - [[Scope|Tutorial: Scope]] | |
| 44 | + | - [[Singleton Pattern|singleton pattern]] | |
| 45 | + | - [Article “Global variable” on the English Wikipedia](https://en.wikipedia.org/wiki/Global_variable) | |
| 46 | + | ||
| 47 | + | --- | |
| 48 | + | *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](/wiki-contact).* | |
| 49 | + | Category: Code |