如何最好地将 VARIANT_BOOL 转换为 C++ bool？
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How to best convert VARIANT_BOOL to C++ bool?
提问by sharptooth
When using COM boolean values are to be passed as VARIANT_BOOL which is declared in wtypes.h as short. There are also predefined values for trueand false:
使用 COM 时，布尔值将作为 VARIANT_BOOL 传递，在 wtypes.h 中声明为short。true和false也有预定义的值：
#define VARIANT_TRUE ((VARIANT_BOOL)-1)
#define VARIANT_FALSE ((VARIANT_BOOL)0)
Which is the best way to convert from VARIANT_BOOL to C++ booltype? Obvious variants are:
从 VARIANT_BOOL 转换为 C++bool类型的最佳方法是什么？明显的变体是：
compare with VARIANT_FALSE
simply cast to bool
与 VARIANT_FALSE 比较
简单地强制转换为 bool
Other ways can be easily invented.
可以很容易地发明其他方法。
Which is the best way to do this - most readable, most standart-compliant, least prone to accidential bugs planting and least prone to issues with porting to 64-bit platforms?
哪个是最好的方法 - 最易读、最符合标准、最不容易出现意外的错误种植以及最不容易出现移植到 64 位平台的问题？
回答by 1800 INFORMATION
Compare to VARIANT_FALSE. There is a lot of buggy code out there that mistakenly passes in the C++ bool truevalue (cast to the integer value 1) to a function expecting VARIANT_BOOL. If you compare to VARIANT_FALSE, you will still get the correct expected value.
比较VARIANT_FALSE。有很多错误代码错误地将 C++ booltrue值（转换为整数值 1）传递给期望VARIANT_BOOL. 如果与 进行比较VARIANT_FALSE，您仍然会得到正确的预期值。
回答by Euro Micelli
I don't like to have to worry about compatibility between different boolean values, so I will normally write:
我不喜欢担心不同布尔值之间的兼容性，所以我通常会写：
VARIANT_BOOL vb_bool = VARIANT_FALSE;
// ... vb_bool set to something by some other code
bool myBool = (vb_bool == VARIANT_TRUE);
Are there tinier (as in "will compile to simpler x86 code"), valid ways to do it? Of course. Not worth it. This is guaranteed to work, so I can worry about my business logic.
是否有更小的（如“将编译为更简单的 x86 代码”），有效的方法？当然。不值得。这保证有效，所以我可以担心我的业务逻辑。
回答by Matthew Flaschen
Casting to bool is obviously wrong. Some people say (e.g. comments at BOOL vs. VARIANT_BOOL vs. BOOLEAN vs. bool) to compare to VARIANT_FALSE, but I would compare to both. That way you catch invalid values (anything but VARIANT_FALSE or VARIANT_TRUE) early.
转换为 bool 显然是错误的。有人说（例如BOOL vs. VARIANT_BOOL vs. BOOLEAN vs. bool 的评论）与 VARIANT_FALSE进行比较，但我会比较两者。这样您就可以尽早捕获无效值（除了 VARIANT_FALSE 或 VARIANT_TRUE 之外的任何值）。
e.g.
例如
bool VariantBoolToBool(VARIANT_BOOL varFlag)
{
bool boolFlag;
switch( varFlag )
{
case VARIANT_TRUE:
boolFlag = true;
break;
case VARIANT_FALSE:
boolFlag = false;
break;
default:
throw Exception("Not a valid value");
}
return boolFlag;
}
回答by Jesus Fernandez
Declare this macro in one of your global headers.
在您的全局标头之一中声明此宏。
#define b(X) ((X)!=VARIANT_FALSE)
EDIT: Much safer version:
编辑：更安全的版本：
inline bool b(VARIANT_BOOL v){return v!=VARIANT_FALSE;}
回答by Pod
Why have an explicit cast?
为什么要有明确的演员表？
if (my_bool)
{
blargh();
}
else
{
blarglerr();
}
This way, true is true and false is false, as per the C standard. If you need to SET a C++ style boolthen do something like:
这样，按照 C 标准，真为真，假为假。如果您需要设置 C++ 样式，bool请执行以下操作：
VARIANT_BOOL vb_bool = VARIANT_FALSE
bool cpp_bool = !!vb_bool
回答by Ruben Bartelink
Standard C++ conversion rules rely on zero meaning false [and as 1800 INFORMATION points out, the TRUE variant is where the most confusion happens] and nothing more. Hence a static_cast would be best.
标准 C++ 转换规则依赖于 0 表示 false [并且正如 1800 INFORMATION 指出的那样，TRUE 变体是最容易混淆的地方]，仅此而已。因此 static_cast 将是最好的。
But in many cases, the code would be more readable as a comparison. In that case, VARIANT_BOOL is the thing to compare with.
但在许多情况下，作为比较，代码会更具可读性。在这种情况下， VARIANT_BOOL 是要比较的东西。
