如何使用_variant_t访问器函数？ [英] How are _variant_t accessor function used?

问题描述

我正在编写一个数据库访问类，最终将返回一个_variant_t作为结果。我需要提取返回的数据。最初我打算将它转换为所需的类型，但是ITS知道它不是必要的所有我应该do是使用访问者。



请问如何使用访问者。

如果我在leasd显示一行，我会很感激代码访问变量并将评估结果分配给变量。



请在此处查看相关问题：



http://www.codeproject.com/Questions/722847/Can-the-void-pointer-returned-by-SafeArrayGetElemeI

I am writing a database access class that will eventually return a _variant_t as result.I need to extract the returned data.Initially I intended to cast it to the desired type but ITS learnt that it insn't neccessary all I ought to do is use the accessor.

Please how does one use an accessor.
Id appreciate it if I am shown at leasd a line of code that accesses a variant and assigninv the outcome of the assessing to a variable.

See associated question here:

http://www.codeproject.com/Questions/722847/Can-the-void-pointer-returned-by-SafeArrayGetElemeI

推荐答案

_variant_t已定义在comutil.h中，任何人都可以看到。



http://msdn.microsoft.com/en-us/library/ew0bcz27.aspx [ ^ ]



您可能需要使用类型转换来获取适当的提取器。

_variant_t is defined in comutil.h for anyone to see.

http://msdn.microsoft.com/en-us/library/ew0bcz27.aspx[^]

You may need to use a typecast to get the appropriate extractor.

_variant_t <中的提取器/ code> class只是重载的运算符，如 short ， long ， float ， double 等最终最终调用 VariantChangeType API。



语法与类型转换相同 -



Extractors in the _variant_t class are nothing but overloaded operators like short, long, float, double etc. that finally end up calling the VariantChangeType API.

The syntax would be the same as a type cast -

_variant_t var(25.4);

short s = (short)var;
long l = (long)var;

OR

short s = short(var);
long l = long(var);

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