错误的功能被选中 [英] wrong function being picked

问题描述

我试图清除一些使用 char * 和 std :: string 的代码，

I was trying to clean up some code that uses char* with std::string and ran into a problem that is illustrated by the following code.

void Foo( int xIn , const std::string & fooIn )
{
    std::cout << "string argument version called \n";
}

void Foo( int xIn ,  bool flagIn = true )
{
    std::cout << "bool argument version called \n";
}

int main()
{
    int x = 1;
    Foo( x , "testing" );
    return 0;
}

当我运行程序时，我获得 bool参数版本<强>。是 char * 到 bool 转换优先于 char * 到 const std :: string& 或者是Visual Studio 2008在我身上玩耍？

When I run the program I get bool argument version called. Is a char* to bool conversion preferred over char* to const std::string& or is Visual Studio 2008 playing tricks on me ?

推荐答案

令人惊讶的是，这种行为是，编译器兼容： char * 到 bool 转换为 std :: string 。

阅读更多这里。

在C ++标准中。它们非常复杂，但以下段落至关重要：

The exact rules are spelled out in the C++ standard. They're surprisingly complicated, but the following paragraph is crucial here:

C ++ 11 13.3.3.2排序隐式转换序列[over.ics.rank]

2
当比较隐式转换序列的基本形式（如13.3中定义的
） 3.1） - 标准转换序列（13.3.3.1.1）是
a比用户定义的转换序列更好的转换序列
或省略号转换序列

2 When comparing the basic forms of implicit conversion sequences (as defined in 13.3.3.1) — a standard conversion sequence (13.3.3.1.1) is a better conversion sequence than a user-defined conversion sequence or an ellipsis conversion sequence

char * -to - bool 需要标准转换序列 char * -to - string 需要用户定义的转换序列。因此，前者是首选。

char*-to-bool requires a "standard conversion sequence" whereas char*-to-string requires a "user-defined conversion sequence". Therefore, the former is preferred.

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