c++ - 在c++中搜索特定行后，如何在文件末尾附加文本？

Question

我有一个文件，必须逐行搜索，然后从找到的行中找到第一个单词和第二个单词，然后在找到的行的末尾附加一个text(变量list_of_names)。我有以下代码，但是将文本附加到文件末尾，而不是在特定行上

    string line;
    string courseid, course_section;
    cout<<"What is a courseID: ";
    cin>>courseid;
    cout<<"What is the  course section: ";
    cin>>course_section;

    string first;
    ofstream outfile;
    outfile.open("course_students.csv", ios_base::app);
    ifstream file;
    file.open("course_students.csv");
    
    if(outfile.is_open()){ 
                while(getline(file, line)) { 
                    stringstream sst(line); 
                    string section;

                    getline(getline (sst,first,','),section, ',');
                    //cout<<first<<endl;
                    if (courseid==first && course_section==section) {
                        //outfile<<save1;
                        outfile<<list_of_names;
                    }
            }
}

outfile.close();
}

我的csv如下:

CSCI-UA.0465,1,
CSCI-UA.0473,1,
CSCI-UA.0470,1,
CSCI-UA.0453,1,
CSCI-UA.0421,1,
CSCI-UA.0310,1,
CSCI-UA.0201,1,
CSCI-UA.0102,5,
CSCI-UA.0101,2,
CSCI-UA.0101,1,
CSCI-UA.0061,1,
CSCI-UA.0060,1,
CSCI-UA.0004,4,
CSCI-UA.0004,1,
CSCI-UA.0002,3,
CSCI-UA.0002,2,
CSCI-GA.3033,13,
CSCI-GA.3033,10,
CSCI-GA.3033,2,
CSCI-GA.3033,1,

任何帮助将不胜感激!

Answer 1

下面这将在输出上创建一个新文件(course_students_output.csv)，您可以随后对其进行重命名。

    string line;
    string courseid, course_section;
    cout<<"What is a courseID: ";
    cin>>courseid;
    cout<<"What is the  course section: ";
    cin>>course_section;

    //string first;
    ifstream file("course_students.csv");
    ofstream outfile("course_students_output.csv");

    if ( file.is_open() ) {
        while ( getline(file, line) ) {
            stringstream sst(line, ios_base::in | ios_base::app | ios_base::out);
            outfile << sst.str();
            
            string first, section;
            getline(getline(sst,first,','), section, ',');
            if (courseid==first && course_section==section) {
                outfile << " " << list_of_names;
            }
            outfile << '\n';
        }
    }

    file.close();
    outfile.close();
}

如果还希望在文件末尾重复添加了 list_of_names的行，请通过以下方式在条件主体内添加一个新的 stringstream对象:

    // ... previous code from above
    if ( file.is_open() ) {
        stringstream end_sst(ios_base::in | ios_base::app | ios_base::out);
        while ( getline(file, line) ) {
            stringstream sst(line, ios_base::in | ios_base::app | ios_base::out);
            outfile << sst.str();

            string first, section;
            getline(getline(sst,first,','), section, ',');
            if (courseid==first && course_section==section) {
                end_sst << line << " " << list_of_names << '\n';
                outfile << " " << list_of_names;
            }
            outfile << '\n';
        }
        outfile << end_sst.str();
    }
    // add end lines from above...