在find_if中使用谓词

问题描述

我有一个这样的结构。

I have a struct like this.

struct MaxWinPerElementInfo
{
   std::string paytableName;
   std::string elementName;
   long long  elementCredits;
   bool        multiplierRequired;
};

我想找到与 paytableName 。为此，我计划将 std :: find_if 与谓词函数一起使用。

I want to find the element that matches the paytableName. For that I planned to use std::find_if with a predicate function.

我在 struct MaxWinPerElementInfo as，

bool operator() ( const MaxWinPerElementInfo &elementInfo ) const
{
    return paytableName == elementInfo.paytableName;
}

现在我尝试通过调用来搜索元素，

Now I tried searching for the element by calling,

std :: find_if（elementInfo.begin（），elementInfo.end（），MaxWinPerElementInfo（paytable））;

其中
elementInfo 是 std :: vector< struct MaxWinPerElementInfo> 和 paytable 是 std :: string 。

为此，我遇到了错误，参数1的未知转换从'std :: string {aka std :: basic_string< char>}'到'const MaxWinPerElementInfo&'

For this I am getting the error, no known conversion for argument 1 from ‘std::string {aka std::basic_string<char>}’ to ‘const MaxWinPerElementInfo&’

我不能使用c ++ 11，因为这是一个遗留代码。

I cannot use c++11 since this is a legacy code.

我在这里缺少什么？任何建议都将真正有用。

What I am missing here? Any suggestions would be really helpful.

推荐答案

std::find_if( elementInfo.begin(), elementInfo.end(),
    MaxWinPerElementInfo( paytable));

您正在尝试通过以下方式构造 MaxWinPerElementInfo 传递一个字符串。您是否有接受字符串的构造函数？我想不是，编译器会尝试调用采用const MaxWinPerElementInfo 引用的副本构造函数。如果没有定义使用单个参数的构造函数，则编译器将还原为它知道的唯一一个：复制构造函数。

You are trying to construct a MaxWinPerElementInfo by passing it a string. Do you have a constructor taking a string? I guess not so the compiler tries to call copy constructor which takes a const MaxWinPerElementInfo reference. If no constructor taking a single argument is defined, compiler will revert to the only one it knows: Copy contructor.

由于您有一个结构且成员是公共的，所以我会

Since you have a struct and members are public, I would suggest implementing this outside of the class with a functor object.

struct MaxWinPerElementInfoPayTablePredicate
{
    MaxWinPerElementInfoPayTablePredicate(const std::string& _paytableName) :
        paytableName(_paytableName) {}

    bool operator() ( const MaxWinPerElementInfo &elementInfo ) const
    {
        return paytableName == elementInfo.paytableName;
    }

    std::string paytableName;
}

然后这样称呼它：

std::find_if( elementInfo.begin(), elementInfo.end(),
    MaxWinPerElementInfoPayTablePredicate(paytable) );

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