delphi 的结构体对齐关键字

最新推荐文章于 2023-11-22 21:26:18 发布

weixin_30436891

最新推荐文章于 2023-11-22 21:26:18 发布

阅读量174

点赞数

CC 4.0 BY-SA版权

原文链接：http://www.cnblogs.com/h2zZhou/p/6774624.html

本文详细介绍了Delphi编译器中$A指令的使用方法及其对记录类型字段对齐的影响。该指令控制编译器为对齐字段而引入填充的最大对齐方式。文章还解释了不同状态（如{$A1}

Align fields (Delphi)

Go Up to Delphi Compiler Directives (List) Index

Type	Switch
Syntax	{$A+}, {$A-}, {$A1}, {$A2}, {$A4}, {$A8} or {$A16} {$ALIGN ON}, {$ALIGN OFF}, {$ALIGN 1}, {$ALIGN 2}, {$ALIGN 4}, {$ALIGN 8} or {$ALIGN 16}
Default	{$A8} {$ALIGN 8}
Scope	Local

Remarks

The $A directive controls the maximum alignment used by the compiler when introducing padding to align a field.

In the {$A1} or {$A-} state, fields are never aligned. All record and class structures are packed.

In the {$A2} state, fields in record types that are declared without the packed modifier and fields in class structures are aligned on word boundaries.

In the {$A4} state, fields in record types that are declared without the packed modifier and fields in class structures are aligned on doubleword boundaries.

In the {$A8} or {$A+} state, fields in record types that are declared without the packed modifier and fields in class structures are aligned on quadword boundaries.

In the {$A16} state, fields in record types that are declared without the packed modifier and fields in class structures are aligned on double quadword boundaries.

Record type field alignment is described in the Delphi Language Guide at Internal Data Formats (Delphi)#Record_Types.

Regardless of the state of the $A directive, variables and typed constants are always aligned for optimal access. In the {$A8} state, execution will be faster.

For OS X applications, stack alignment must be on 16-byte boundaries. For details, see Eli Boling's blog at http://blogs.embarcadero.com/eboling/2009/05/20/5607.

转载于:https://www.cnblogs.com/h2zZhou/p/6774624.html