C ++：从文件中读取字符串和整数，并获得最高编号

问题描述 投票：-1回答：3

我编写了下面的代码，试图从文本文件中读取字符串和整数，其中整数是最大数字（得分）及其对应的字符串（播放器）。我能够cout文件的内容，但我如何测试哪个数字是最高的，我如何将其链接到其播放器？任何帮助将不胜感激，谢谢！

文本文件的内容：

Ronaldo 
10400 
Didier 
9800 
Pele 
12300 
Kaka 
8400 
Cristiano 
8000

码：

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

using namespace std;

int main() { 


    string text;
    string player;

    int scores;
    ifstream scoresFile;


    // Open file
    scoresFile.open("scores.txt");

    // Check if file exists
    if (!scoresFile) {
        cerr << "Unable to open file: scores.txt" << endl;
        exit(0); // Call system to stop
    }
    else {
        cout << "File opened successfully, program will continue..." << endl << endl << endl;

        // Loop through the content of the file
        while (scoresFile >> text) {

        cout << text << endl;

        }
    }

    // Close file
    scoresFile.close();

    return 0;
}
c++
3个回答
0
投票

做一个变量string bestplayer，string currentplayer和int bestscore = 0。每次读一行我都会增加一个整数。然后，你将它的模数相对于两个（i % 2），如果它是奇数，你将流输出到currentplayer。如果是偶数，则将流输出为临时整数并将其与bestscore进行比较。如果它高于bestscore，则将bestscore的值设置为该整数并设置bestplayer = currentplayer。祝你好运！

0
投票

当你不是必须时，不要使用exit()。 exit()不会进行任何堆栈解除并绕过RAII的原则。在main()中，如果出现错误，您可以轻松使用return EXIT_FAILURE;结束程序。

谈论RAII：使用构造函数给class它的值，例如。使用std::ifstream scoresFile{ "scores.txt" }; instead ofscoresFile.open（“scores.txt”）; . Also, there is no need to callscoresFile.close（）`因为析构函数会处理它。

如果你想说的只是std::endl（或'\n'），请不要使用"...\n"。 std::endl不仅会在流中插入换行符（'\n'），还会将其刷新。如果你真的想要刷新流然后显式并写std::flush而不是std::endl。

现在到手头的问题。优雅的解决方案是拥有一个代表player的对象，其中包含玩家名称和分数。这样的对象不仅可以用于读取高分榜，还可以用于游戏过程中。

为了输入和输出，会使流插入和提取操作符过载。

#include <cstdlib>
#include <iostream>
#include <string>
#include <fstream> 

class player
{
    std::string name;
    int score;

    friend std::ostream& operator<<(std::ostream &os, player const &p);
    friend std::istream& operator>>(std::istream &is, player &p);

public:
    bool operator>(player const &other) { return score > other.score; }
};

std::ostream& operator<<(std::ostream &os, player const &p)
{
    os << p.name << '\n' << p.score;
    return os;
}

std::istream& operator>>(std::istream &is, player &p)
{
    player temp_player;
    if (is >> temp_player.name >> temp_player.score)
        p = temp_player; // only write to p if extraction was successful.
    return is;
}

int main()
{
    char const * scoresFileName{ "scores.txt" };
    std::ifstream scoresFile{ scoresFileName };

    if (!scoresFile) {
        std::cerr << "Unable to open file \"" << scoresFileName << "\"!\n\n";
        return EXIT_FAILURE;
    }

    std::cout << "File opened successfully, program will continue...\n\n";

    player p;
    player highscore_player;

    while (scoresFile >> p) { // extract players until the stream fails
        if (p > highscore_player) // compare the last extracted player against the previous highscore
            highscore_player = p; // and update the highscore if needed
    }

    std::cout << "Highscore:\n" << highscore_player << "\n\n";
}
0
投票

除了重载<<运算符之外，您还可以采用更多的程序方法，只需检查读取行中的第一个字符是否为数字，如果是，则将int转换为std::stoi并与当前最大分数进行比较，更新if它更大。

您的数据文件布局有点奇怪，但假设它是您必须使用的，您可以简单地读取第一行作为名字，并在读取循环结束时将名称存储为lastname，以便它是在下一行读取整数时可用。

利用std::exception验证std::stoi转换将确保您在进行比较和更新高分之前处理有效的整数数据，例如

    // Loop through the content of the file
    while (scoresFile >> text) {
        if ('0' <= text[0] && text[0] <= '9') { /* is 1st char digit? */
            try {   /* try and convert to int */
                int tmp = stoi (text);
                if (tmp > scores) {         /* if tmp is new high score */
                    scores = tmp;           /* assign to scores */
                    player = lastplayer;    /* assign lastplayer to player */
                }
            }   /* handle exception thrown by conversion */
            catch ( exception& e) {
                cerr << "error: std::stoi - invalid argument or error.\n" <<
                        e.what() << '\n';
            }
        }
        else    /* if 1st char not a digit, assign name to lastplayer */
            lastplayer = text;

    }

另一个说明。初始化变量以在大于比较中使用时，应将值初始化为INT_MIN以确保正确处理负值。 （对于小于比较，初始化为INT_MAX）

完全放在一起，你可以做类似的事情：

#include <iostream>
#include <string>
#include <fstream> 
#include <limits>

using namespace std;

int main() { 


    string text;
    string player;
    string lastplayer;

    int scores = numeric_limits<int>::min();    /* intilize to INT_MIN */
    ifstream scoresFile;

    // Open file
    scoresFile.open("scores.txt");

    // Check if file exists
    if (!scoresFile) {
        cerr << "Unable to open file: scores.txt" << endl;
        exit(0); // Call system to stop
    }

    cout << "File opened successfully, program will continue..." << 
            endl << endl;

    // Loop through the content of the file
    while (scoresFile >> text) {
        if ('0' <= text[0] && text[0] <= '9') { /* is 1st char digit? */
            try {   /* try and convert to int */
                int tmp = stoi (text);
                if (tmp > scores) {         /* if tmp is new high score */
                    scores = tmp;           /* assign to scores */
                    player = lastplayer;    /* assign lastplayer to player */
                }
            }   /* handle exception thrown by conversion */
            catch ( exception& e) {
                cerr << "error: std::stoi - invalid argument or error.\n" <<
                        e.what() << '\n';
            }
        }
        else    /* if 1st char not a digit, assign name to lastplayer */
            lastplayer = text;

    }
    // Close file
    scoresFile.close();

    cout << "Highest Player/Score: " << player << "/" << scores << '\n';

    return 0;
}

示例使用/输出

$ ./bin/rdnamenum2
File opened successfully, program will continue...

Highest Player/Score: Pele/12300

仔细看看，如果您有其他问题，请告诉我。

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