c++ - 读取文件并在 C++ 中拆分行

Question

我有以下代码从 txt 文件中读取输入，如下所示

Paris,Juli,5,3,6 
Paris,John,24,2 
Canberra,John,4,3 
London,Mary,29,4,1,2

我的代码是将数据加载到 map 中，然后我想打印 map 内容以确保它已被正确插入，我检查了 m 的值，因为它在拆分线时使用了它。但是，在执行过程中，我将其继续为 0，这意味着它永远不会进入 while 循环。我以前使用过这部分代码并且它有效。我找不到哪里出错了。

#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>
#include <vector>
#include<map>
using namespace std;

struct info {
       string Name;
       int places;// i will use the binary value to identfy the visited places example 29 is 100101 
             // this means he visited three places (London,LA,Rome)   
       vector<int> times; // will represent the visiting time,e.g. 1,2,5 means london 1 time, LA 
                   // twice and Rome five times 


       };
map<string,vector<info> > log;
map<string,vector<info> >::iterator i;
fstream out;
int main() {
    out.open("log.txt", std::ios::in | std::ios::out | std::ios::app);
            string line;
            char* pt;
            string temp[19];

    // for each line in the file 
    while (!out.eof())
    {
         getline(out,line);//read line from the file
         pt=strtok(&line[0],"," );//split the line
         int m=0;
         while (pt != NULL)
         {
         temp[m++] = pt; // save the line info to the array
         cout<<m<<"  ";
         pt = strtok (NULL, ",");
         }
         cout<<m<<"  "; // during the execution I get this as continues 0s which means it is never enter the while loop
         info tmp;
         // read the other data
         tmp.Name=temp[1];
         tmp.places=atoi(temp[2].c_str());
         for ( int i=3;i<=m;i++)
         { 
         tmp.times.push_back(atoi(temp[i].c_str()));
         }         
         // create a new object 
         log[temp[0]].push_back(tmp); 
         }

 vector<int>::iterator j; 
    for(i=log.begin();i!=log.end();i++) {
    cout<< "From "<< i->first<<" city people who travels: "<<endl; 
    for (size_t tt = 0; tt < (i->second).size(); tt++) {
    cout<< (i->second[tt]).Name<< " went to distnations "<< (i->second)[tt].places<<" \nwith the folloing number of visiting time "; 
    for (j=((i->second[tt]).times).begin();j!= ((i->second[tt]).times).end();j++) 
    cout<<*j<<" ";
     } 
    }  


          system("PAUSE");
          return 0;
          }

Answer 1

这是一个错误

// for each line in the file 
while (!out.eof())
{
     getline(out,line);//read line from the file

应该是

// for each line in the file 
while (getline(out,line))
{

坦率地说，我发现这个错误重复出现的频率令人难以置信。 eof 并不像您认为的那样。它测试 last 读取是否因文件结尾而失败。您正在使用它来尝试预测下一次读取是否会失败。它根本不是那样工作的。

这一行是错误的

pt=strtok(&line[0],"," );//split the line

strtok 适用于 C 字符串，不能保证它适用于 std::string。

但这些都不太可能是您真正的错误。我建议仅使用 ios::in 打开文件。毕竟你只想从中读取。