在C ++中将默认值参数放在可变长度函数中的哪里? [英] where to place default value parameter in variable-length function in c++?
问题描述
在可变长度参数函数中,"..."必须放在最后.并且启用默认值的参数也必须是最后一个.
in variable-length parameters function, the '...' must be place last. And default value enabled parameters must be last, too.
那么,在同一个函数中同时需要两者吗?
so, how about both needed in the same one function?
现在我有一个日志实用程序:MyPrint(int32_t logLevel,const char * format,...),用于根据'logLevel'打印日志.
Now I have a log utility: void MyPrint(int32_t logLevel, const char *format, ...), which used to print log according to 'logLevel'.
但是,有时我希望它可以用作:MyPrint("Log test number%d",number),不需要'logLevel'.
However, sometimes I hope it can be used as: MyPrint("Log test number%d", number), without 'logLevel' needed.
问题:默认参数和可变参数函数没有帮助.
推荐答案
在您的特定情况下,您可能只想制作两个版本的MyPrint,例如:
In your specific case you might just want make two versions of MyPrint, like:
MyPrint(const char *format, ...)
{
_logLevel = 1;
// stuff
}
MyPrint(int32_t logLevel, const char *format, ...)
{
_logLevel = logLevel;
//stuff
}
另一方面,命名参数成语确实可以提供替代解决方案:
On the other hand the Named Parameter Idiom would indeed provide an alternative solution:
class Abc
{
public:
MyPrint(const char *format, ...)
{
_logLevel = 1;
// stuff
}
Abc &setLogLevel(int32_t logLevel)
{
_logLevel = logLevel;
}
// stuff
};
因此您可以像这样调用MyPrint():
So you could call MyPrint() like this:
MyPrint("blah,blah", 123);
或这样:
MyPrint("blah,blah", 123).setLogLevel(5);
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