尝试从文本文件中打印名字，但同时获取名字和中间名 [重复]

Posted 2023-02-22

【中文标题】尝试从文本文件中打印名字，但同时获取名字和中间名 [重复]

【英文标题】：Trying to print first name from a text file, but getting both first and middle name [duplicate]

【发布时间】：2019-11-22 00:18:54

【问题描述】：

我正在尝试从格式如下的文本文件中打印名字、中间名和姓氏：

Doe, John Bob
Young, Tim Joe
Washington, George Peter

这是预期的输出：

First name: John
Middle name: Bob
Last name: Doe

First name: Tim
Middle name: Joe
Last name: Young

First name: George
Middle name: Peter
Last name: Washington

我能够正确获取中间名和姓氏，但是当我尝试获取名字时，它显示它是名字和中间名。代码如下：

#include <iostream>
#include <fstream>

using namespace std;

int main()

    //Variable for the text file
    ifstream infile;

    //Opens the text file
    infile.open("data.txt");

    //Variables for the names
    string name;
    string lastName;
    string firstName;
    string middleName;

    //Loops through all the names
    while(getline(infile, name))
    
        //Looks for a comma and space in each name
        int comma = name.find(',');
        int space = name.find(' ', comma+2);

        //Splits the name into first, last, and middle names
        lastName = name.substr(0, comma);
        firstName = name.substr(comma+2, space);
        middleName = name.substr(space+1, 100);

        //Prints the names
        cout << "First name: " << firstName << endl;
        cout << "Middle name: " << middleName << endl;
        cout << "Last name: " << lastName << endl;
        cout << endl;
    
    //closes the text file
    infile.close();

    return 0;
//end main

这是我得到的输出：

First name: John Bob
Middle name: Bob
Last name: Doe

First name: Tim Joe
Middle name: Joe
Last name: Young

First name: George Peter
Middle name: Peter
Last name: Washington

【问题讨论】：

您是否尝试过使用调试器逐行单步执行代码，同时在每个执行步骤检查每个变量的值？

可能重复：How to use string.substr() function?

函数substr()的第二个参数是新字符串中应该包含的字符数。你放入长度的值是从std::string::find()返回的，这个函数返回的值是字符串中的位置（不是从搜索开始的长度）。

【参考方案1】：

您在滥用substr() 方法，来自reference

子字符串是从字符位置 pos 开始并跨越 len 个字符（或直到字符串末尾，以先到者为准）的对象部分。

第二个参数是子字符串的长度。如果你使用

first = name.substr(comma+2, space-comma-2)

你应该得到你预期的行为。

【参考方案2】：

更简单的选择：

#include <iostream>
#include <fstream>
#include <sstream>
#include <string>

// is evil. Avoid.
//using namespace std;

int main()

    std::ifstream infile("data.txt"); // open file

    std::string line;
    while(std::getline(infile, line)) // get a line
    
        std::istringstream stream(line); // make an input stream out of the line

        std::string lastName;
        std::string firstName;
        std::string middleName;
        if (getline(stream, lastName, ',') // read up to the comma and discard the comma 
                && stream >> firstName // read up to the next space 
                          >> middleName) // read up to next space, but end of line comes first
        
            std::cout << "First name: " << firstName << '\n'   // endl very expensive
                      << "Middle name: " << middleName << '\n' // save endl for when 
                      << "Last name: " << lastName << '\n'     // you really need it
                      << std::endl; //probably don't even need it here.
        
    
// file closes automatically

Documentation for std::istringstream

补充阅读：Why is "using namespace std;" considered bad practice?和C++: "std::endl" vs "\n"

请注意，这不能处理像 John Jacob Jingleheimer Schmidt 这样的名字，但可以很容易地修改为这样做。