?

delphi枚舉類型長度默認為2個字節(單字)，而在C中枚舉為4個字節(雙字)，如果需要跨這兩個平臺編程，傳輸結構時會由于數據長度不一造成災難。

經過查找資料，原來delphi可以通過{$Z+} {$Z-} {$Z1} {$Z4} 等宏設置枚舉類型的長度，小至1個字節，大至4個字節。

官方說明如下：

http://docs.embarcadero.com/products/rad_studio/delphiAndcpp2009/HelpUpdate2/EN/html/devcommon/compdirsminimumenumerationsize_xml.html

The $Z directive controls the minimum storage size of Delphi enumerated types.?

An enumerated type is stored as an unsigned byte if the enumeration has no more than 256 values, and if the type was declared in the {$Z1} state (the default). If an enumerated type has more than 256 values, or if the type was declared in the {$Z2} state, it is stored as an unsigned word. Finally, if an enumerated type is declared in the {$Z4} state, it is stored as an unsigned double word.?

The {$Z2} and {$Z4} states are useful for interfacing with C and C++ libraries, which usually represent enumerated types as words or double words.

Note: Note: For backwards compatibility with early versions of Delphi and CodeGear Pascal, the directives {$Z-} and {$Z+} are also supported. They correspond to {$Z1} and {$Z4}, respectively.

例子如下：

http://www.delphibasics.co.uk/RTL.asp?Name=$Z

Example code : Various enum type sizes

type
? {$Z1}
? TCars1? = (Rover, Jaguar, Honda);??? // Will fit into 1 byte
? TFruit1 = (Banana=255, Apple, Pear); // Will exceed one byte
? {$Z4}
? TCars2? = (Ford, Nissan, Vauxhall);? // Now uses 4 bytes
? TFruit2 = (Orange=255, Plum, Grape); // Now uses 4 bytes
begin
? ShowMessage('TCars1? size = '+IntToStr(SizeOf(TCars1)));
? ShowMessage('TFruit1 size = '+IntToStr(SizeOf(TFruit1)));
? ShowMessage('TCars2? size = '+IntToStr(SizeOf(TCars2)));
? ShowMessage('TFruit2 size = '+IntToStr(SizeOf(TFruit2)));
end;

?? TCars1? size = 1
?? TFruit1 size = 2
?? TCars2? size = 4
?? TFruit2 size = 4

轉載于:https://www.cnblogs.com/h2zZhou/p/5000153.html

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