Question

我正在将文件中的某些数据读入vector<struct>。代码是这样的：

#include <fstream>
#include <map>
#include <string>
#include <vector>
#include <algorithm>   

using namespace std;

int main()
{
    ifstream fin("gift1.in", ios::in);
    ofstream fout("gift1.out", ios::out);

    unsigned short NP;

    struct person
    {
        string name;
        unsigned int gave;
        unsigned int received;
    };

    vector<person> accounts;

    string tmp_name;

    fin >> NP;
    accounts.resize(NP);
    for (auto i : accounts)
    {
        fin >> tmp_name;
        fout << "Just read this name: " << tmp_name << "\n";
        i.name = tmp_name;
        i.gave = 0;
        i.received = 0;

        fout << "We have just created this person: " << i.name << ";" << i.gave << ";" << i.received << "\n";
//(1)
        // OK, this part works
    }

    fout << "Freshly created ledger:\n";
    for (auto l : accounts)
        fout << "Person: " << l.name << "; Gave: " << l.gave << ";Received " << l.received << "\n";
//irrelevant stuff further
}

问题是名称在(1)循环中打印出来，但它们不在循环范围内。为什么会这样？

示例输出为：

Just_read_this_name：_mitnik We_have_just_created_this_person：_mitnik; 0; 0 Just_read_this_name：_Poulsen We_have_just_created_this_person：_Poulsen; 0; 0 Just_read_this_name：_Tanner We_have_just_created_this_person：_Tanner; 0; 0 Just_read_this_name：_Stallman We_have_just_created_this_person：_Stallman; 0; 0 Just_read_this_name：_Ritchie We_have_just_created_this_person：_Ritchie; 0; 0 Just_read_this_name：_Baran We_have_just_created_this_person：_Baran; 0; 0 Just_read_this_name：_Spafford We_have_just_created_this_person：_Spafford; 0; 0 Just_read_this_name：_Farmer We_have_just_created_this_person：_Farmer; 0; 0 Just_read_this_name：_Venema We_have_just_created_this_person：_Venema; 0; 0 Just_read_this_name：_Linus We_have_just_created_this_person：_Linus; 0; 0 Freshly_created_ledger：联系人：_; _都给：_0; Received_0 联系人：_; _都给：_0; Received_0 联系人：_; _都给：_0; Received_0 联系人：_; _都给：_0; Received_0 联系人：_; _都给：_0; Received_0 联系人：_; _都给：_0; Received_0 联系人：_; _都给：_0; Received_0 联系人：_; _都给：_0; Received_0 联系人：_; _都给：_0; Received_0 人：_; _都给：_0; Received_0

Answer 1

for (auto i : accounts)

您获得的每个i都是accounts中元素的副本。执行i.name = tmp_name时，您只需修改此副本。您需要使用引用，以便您可以自己修改元素：

for (auto& i : accounts)

无法从具有字符串成员的结构向量中读取名称

1 个答案: