如何将Lambda用于std :: find_if [英] How to use lambda for std::find_if

问题描述

我正在尝试使用std :: find_if查找符合某些条件的对象.请考虑以下内容:

I am trying to use std::find_if to find an object that matches some criteria. Consider the following:

struct MyStruct         
{
    MyStruct(const int & id) : m_id(id) {}                      
    int m_id;
};
...         
std::vector<MyStruct> myVector; //... assume it contains things

MyStruct toFind(1);
std::vector<MyStruct>::iterator i = std::find_if(myVector.begin(), myVector.end(), ???);

我不确定要在???

我看到的所有示例都有一个lambda，该lambda使用硬编码的值来检查ID.我想要的是仅在toFind的ID与向量中一项之一的ID匹配时才返回迭代器/成功.

All the examples I have seen have a lambda that uses a hard-coded value to check for the ID. What I want is to return the iterator/success only if the id of toFind matches the id of one of the items in the vector.

我看到的所有示例都没有向我展示如何传递两个参数

All the examples I have see don't show me how to pass the two parameters

编辑

其他信息 我必须使用两种不同的方案 其中有一个==运算符的结构 另一个结构中没有运算符==，并且我无法创建一个，因为针对这种情况查找匹配项的标准不像对等运算符那样严格.

Additional info There are two different scenarios I have to use this for One in which there is an == operator for the struct and another in which there is no operator == for the struct - and i can't create one because the criteria for finding a match for this scenario is not as rigid as would be used for an equivalence operator.

(感谢所有答复；我能够在一种情况下使用find()，并且在您的帮助下能够在另一种情况下使用find_if())

(And thanks to all who responded; I was able to use find() in one case and with your help was able to use find_if() for the other)

推荐答案

尝试一下:

std::find_if(
    myVector.begin(), myVector.end(),
    [&toFind](const MyStruct& x) { return x.m_id == toFind.m_id;});

或者，如果为MyStruct定义了适当的==重载，则可以使用find:

Alternatively, if you had defined an appropriate == overload for MyStruct, you could just use find:

std::find(myVector.begin(), myVector.end(), toFind);  // requires ==

当您进行某种异构查找时，通常最好使用find_if版本，例如，如果只给了您int而不是MyStruct值.

The find_if version is usually best when you have some kind of heterogeneous lookup, for example if you were just given an int, not a value of MyStruct.

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