根据find_if从结构向量中检索结构

Question

我编写了这个小程序来搜索结构向量中的结构。在下面代码中的这一行之后，我应该如何提取匹配向量的元素。即结构及其内容。

        if (std::find_if(jobInfoVector.begin(), jobInfoVector.end(), pred) != jobInfoVector.end())

#include <iostream>
#include <vector>
#include <algorithm>
#include "boost/bind.hpp"

using namespace std;
struct jobInfo
{
        std::string jobToken;
        time_t startTime;
        time_t endTime;
};
typedef struct jobInfo JobInfo;

int main()
{
        std::vector<JobInfo> jobInfoVector;
        JobInfo j1 = {"rec1",1234,3456};
        JobInfo j2 = {"rec2",1244,3656};
        JobInfo j3 = {"rec3",1254,8456};

        jobInfoVector.push_back(j1);
        jobInfoVector.push_back(j2);
        jobInfoVector.push_back(j3);

        auto pred = [](const JobInfo &jobinfo) { return jobinfo.startTime == 1234; };

        if (std::find_if(jobInfoVector.begin(), jobInfoVector.end(), pred) != jobInfoVector.end())
        {
                cout << "got a match" << endl;
        }
        else
        {
                cout << "Did not get a match" << endl;
        }

        return 0;
}

Answer 1

您可以将std::find_if()的结果保存为迭代器，然后取消引用以提取其组件。比如：

#include <iostream>
#include <vector>
#include <algorithm>
#include "boost/bind.hpp"

using namespace std;
struct jobInfo
{
        std::string jobToken;
        time_t startTime;
        time_t endTime;
};
typedef struct jobInfo JobInfo;

int main()
{
        std::vector<JobInfo> jobInfoVector;
        JobInfo j1 = {"rec1",1234,3456};
        JobInfo j2 = {"rec2",1244,3656};
        JobInfo j3 = {"rec3",1254,8456};

        jobInfoVector.push_back(j1);
        jobInfoVector.push_back(j2);
        jobInfoVector.push_back(j3);

        auto pred = [](const JobInfo &jobinfo) { return jobinfo.startTime == 1234; };
        auto it = std::find_if(jobInfoVector.begin(), jobInfoVector.end(), pred);
        if (it != jobInfoVector.end())
        {
                jobInfo& match = *it;
                cout << "got a match" << endl;
                //Do whatever job with match
        }
        else
        {
                cout << "Did not get a match" << endl;
        }

        return 0;
}

Answer 2

您只需要保留从std::find_if返回的迭代器，然后使用它。

返回值 满足条件的第一个元素的迭代器，如果没有这样的元素，则为最后一个元素。

例如，您可以应用带有初始化器的If语句 (自C++17)：

if (auto it = std::find_if(jobInfoVector.begin(), jobInfoVector.end(), pred); it != jobInfoVector.end())
{
        cout << "got a match" << endl;
        // use it from here...
}
else
{
        cout << "Did not get a match" << endl;
}