c++ - 逐行读取文件并输出第一列

Question

我是 C++ 的新手，我正在尝试对文件中的 2 个单词(双重和三重)进行字符串搜索，并打印找到它们的行。有的只有“双”字，有的只有“三”字。

代码似乎没有输出单词，它只是在循环结束时打印最后一行。

我忘了补充一点，我需要打印找到单词的行的第一个元素，我能够找到找到单词的行，但是，它似乎没有打印第一个元素文件。

这是我的代码。

int main(int argv, char *argc[]){
    const string filen("test.txt");
    ifstream inFile(filen.c_str());
    string  line = "";

    char IDList[10];
    string ID = "";
    char* double_word = "double"; // test variable to search in file
    char* triple_word = "triple";
    stringstream ss;

    string word = "";
    unsigned int currentLine = 0;

    // iterate through each line and check if the words double or triple exist.

    while(getline(inFile, line)){
            currentLine++;
            if (line.find(double_word) != string::npos) {

                    cout << "found the word \"double\" on line: " << currentLine << endl;
    // this part takes the input file and reads the first character of the line i.e. the ID and adds it to the IDList
    // string array.
                    while(inFile >> IDList){
                            cout << "File Id: " << IDList << endl;
                            inFile.ignore(numeric_limits<streamsize>::max(), ' ');

                            for(int i=0;i<10;i++){
                                    ss << IDList[i] << endl;
                            }
                    word = ss.str();
                    }
            }
            else if(line.find(triple_word) != string::npos){

                    cout << "found the word \"triple\" on line: " << currentLine << endl;

            // now take the id of this file and add it to a different queue.

                    while(inFile >> IDList){
                            cout << "File Id: " << IDList << endl;
                            inFile.ignore(numeric_limits<streamsize>::max(), ' ');

                            for(int i=0;i<10;i++){
                                    ss << IDList[i] << endl;
                            }
                    word = ss.str();
                    }
            }
            else if(line.find(double_word) && line.find(triple_word) != string::npos){

                    cout << "Found both words double and triple in line: " << currentLine << endl;

                    while(inFile >> IDList){
                            cout << "File Id: " << IDList << endl;
                            inFile.ignore(numeric_limits<streamsize>::max(), ' ');

                            for(int i=0;i<10;i++){
                                    ss << IDList[i] << endl;
                            }
                    word = ss.str();
                    }
            }
            else{
                    cout << "neither word found, moving to next line" << endl;
            }
    }

    inFile.close();
    cout << "Id's added to the queue" << word << endl;
    return 0;
}

Answer 1

我认为你可以简化你的代码并编写如下内容:

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

using std::string;
using std::vector;
using std::cout;
using std::cin;

int main(int argc, char* argv[]) {
    const string filen("test.txt");
    std::ifstream inFile(filen.c_str());
    string  line;

    string double_word = "double"; // test variable to search in file
    string triple_word = "triple";

    vector<string> IDs;
    unsigned int currentLine = 0;

    // iterate through each line and check if the words double or triple exist.

    while(getline(inFile, line)){
        currentLine++;
        bool found_d_word = line.find(double_word) != string::npos;
        bool found_t_word = line.find(triple_word) != string::npos;
        if ( found_d_word && !found_t_word ) 
            cout << "found the word \"double\" on line: " << currentLine << '\n';
        if ( found_t_word && !found_d_word ) 
            cout << "found the word \"triple\" on line: " << currentLine << '\n';
        if ( found_d_word && found_t_word ) 
            cout << "Found both words double and triple in line: " << currentLine << '\n';
        if ( found_d_word || found_t_word ) {

            std::istringstream ss{line};

            string ID;
            ss >> ID;
            cout << "File Id: " << ID << '\n';
            // my guess: store all the IDs in one vector
            IDs.push_back(ID);

        } else {
            cout << "neither word found, moving to next line\n";
        }
    }
    inFile.close();
    return 0;
}

您的代码的一个问题是您首先读取输入文件的一行(使用 getline)，将其放入一个字符串中，然后，当在字符串中找到单词“double”或“triple”时，您尝试从文件中读取 ID，而您应该从同一个字符串中读取它。