Absolute/fr: what changed
Revision 0 to 1. Removed lines have a minus sign; added lines have a plus sign.
Title: Absolute/fr
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| 1 | + | Ce [[modifier/fr|modificateur]] de déclaration indique la [[Variable/fr|variable]] déclarée est à la même adresse que la variable qui suit *absolute*. Toutefois, aucune cohérence entre les valeurs des deux variables n'est assurée. | |
| 2 | + | ||
| 3 | + | ``` pascal | |
| 4 | + | Var | |
| 5 | + | sintI: ShortInt; | |
| 6 | + | lintI: LongInt absolute sintI; | |
| 7 | + | ||
| 8 | + | begin | |
| 9 | + | // Affichage correct | |
| 10 | + | lintI := 20; | |
| 11 | + | ShowMessage(inttostr(lintI) + ' ' + inttostr(sintI)); // Anzeige: 20 20 | |
| 12 | + | ||
| 13 | + | // Affichage absurde | |
| 14 | + | lintI := 2000; | |
| 15 | + | ShowMessage(inttostr(lintI) + ' ' + inttostr(sintI)); // Anzeige: 2000 -45 | |
| 16 | + | end; | |
| 17 | + | ``` | |
| 18 | + | ||
| 19 | + | ``` pascal | |
| 20 | + | // Example on little endian x64 processor | |
| 21 | + | Uses SysUtils; | |
| 22 | + | ||
| 23 | + | Var | |
| 24 | + | anInt : Integer; | |
| 25 | + | anotherInt : Integer absolute anInt; | |
| 26 | + | firstByte : Byte absolute anInt; | |
| 27 | + | ||
| 28 | + | begin | |
| 29 | + | // with both Integer variables at the same memory location, a change to one is reflected | |
| 30 | + | // in the other | |
| 31 | + | anInt := 20; | |
| 32 | + | ||
| 33 | + | WriteLn(IntToStr(anInt) + ' ' + IntToStr(anotherInt)); // Outputs: 20 20 | |
| 34 | + | ||
| 35 | + | // a value of 20 fits in the first byte: | |
| 36 | + | ||
| 37 | + | WriteLn('firstByte: ' + IntToStr(firstByte)); // Outputs: firstByte: 20 | |
| 38 | + | ||
| 39 | + | anotherInt := 333; | |
| 40 | + | ||
| 41 | + | WriteLn(IntToStr(anInt) + ' ' + IntToStr(anotherInt)); // Outputs: 333 333 | |
| 42 | + | ||
| 43 | + | // 333 is too large a value to fit in one byte | |
| 44 | + | // little-endian x64 - least significant byte is first in memory: | |
| 45 | + | // 333 = 101001101 = 01001101 00000001 in memory = 0x4D 0x01 = decimal: 77 1 | |
| 46 | + | ||
| 47 | + | WriteLn('firstByte: ' + IntToStr(firstByte)); // Outputs: firstByte: 77 | |
| 48 | + | end. | |
| 49 | + | ``` | |
| 50 | + | ||
| 51 | + | --- | |
| 52 | + | *From the Free Pascal wiki, page "Absolute/fr", as it stood on 2020-12-19 after a change by E-ric, 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).* |