无法从具有字符串成员的结构向量中读取名称

Question

我正在从文件中读取某些数据到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？

示例输出是这样的:

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:Person:_; _ Gave:_0; Received_0 Person:_; _ Gave:_0; Received_0 Person:_; _ Gave:_0; Received_0 Person:_; _ Gave:_0; Received_0 Person:_; _ Gave:_0; Received_0 Person:_ ; _Gave:_0; Received_0 Person:_; _ Gave:_0; Received_0 Person:_; _ Gave:_0; Received_0 Person :_; _ Gave:_0; Received_0 Person:_; _ Gave:_0; Received_0

Answer 1

for (auto i : accounts)

i你得到的每一个都是一个元素的副本accounts.当你这样做时i.name = tmp_name,你只是在修改这个副本.您需要使用引用,以便您可以自己修改元素:

for (auto& i : accounts)