正确的try-catch设计

Question

如何才能使try-catch不会输出两次错误？下面的代码仅用于识别snap、csg、cdh和cr。它像这样打印出来：

Input Strings:
snap(12345,Charlie Brown,Manager,555-1234).

snap(67890,Lucy,Right Field,555-5678).
csg(CS101,12345,A).

csg(CS101,67890,B).

csgs(CS101,67890,B). // i want to get rid of this

**Error: csgs(CS101,67890,B). // repeat
cdh(CS101,M,9AM).

cr(CS101,1170 TMCB).

下面是我的代码：

out << "Input Strings:" << endl;



for (string line; getline(in, line);) {
    out << line;

    try {

        if ("snap(" == line.substr(0, 5)) {
            string studentID = line.substr(5, line.find(',') - 5);
            line = line.substr(line.find(',') + 1);
            string studentName = line.substr(0, line.find(','));
            line = line.substr(line.find(',') + 1);
            string studentAddress = line.substr(0, line.find(','));
            line = line.substr(line.find(',') + 1);
            string studentPhone = line.substr(0, line.find(')'));

            snaps.emplace_back(studentID, studentName, studentAddress, studentPhone);
            continue;
        }
        else if ("csg(" == line.substr(0, 4)) {
            string courseName = line.substr(4, line.find(',') - 4);
            line = line.substr(line.find(',') + 1);
            string studentID = line.substr(0, line.find(','));
            line = line.substr(line.find(',') + 1);
            string studentGrade = line.substr(0, line.find(')'));

            csg.emplace_back(courseName, studentID, studentGrade);
            continue;
        }
        else if ("cdh(" == line.substr(0, 4)) {
            string courseName = line.substr(4, line.find(',') - 4);
            line = line.substr(line.find(',') + 1);
            string courseDay = line.substr(0, line.find(','));
            line = line.substr(line.find(',') + 1);
            string courseTime = line.substr(0, line.find(')'));

            cdh.emplace_back(courseName, courseDay, courseTime);
            continue;
        }
        else if ("cr(" == line.substr(0, 3)) {
            string courseName = line.substr(3, line.find(',') - 3);
            line = line.substr(line.find(',') + 1);
            string courseRoom = line.substr(0, line.find(')'));

            cr.emplace_back(courseName, courseRoom);
            continue;
        }
        throw string(line);

    }
    catch (const runtime_error& error) { out << endl << "**Error: " << error.what(); }
    catch (const string& e) { out << endl << "**Error: " << e; }

}
in.close();

Answer 1

显然，您需要移动out << line;，以便只有在您知道没有错误时才打印它。

我看不出在这段代码中需要异常。异常真的应该为异常情况保留，跳过坏数据并不是真的那样。此外，continue语句通常被认为是不好的风格，同样是因为它们会中断程序的正常流程，使其难以理解。

这是没有异常和没有continue的重写代码。您真正需要做的就是处理else子句中的错误情况，并将行的打印移动到循环的末尾。

out << "Input Strings:" << endl;
for (string line; getline(in, line);) {
    if ("snap(" == line.substr(0, 5)) {
        string studentID = line.substr(5, line.find(',') - 5);
        line = line.substr(line.find(',') + 1);
        string studentName = line.substr(0, line.find(','));
        line = line.substr(line.find(',') + 1);
        string studentAddress = line.substr(0, line.find(','));
        line = line.substr(line.find(',') + 1);
        string studentPhone = line.substr(0, line.find(')'));

        snaps.emplace_back(studentID, studentName, studentAddress, studentPhone);
    }
    else if ("csg(" == line.substr(0, 4)) {
        string courseName = line.substr(4, line.find(',') - 4);
        line = line.substr(line.find(',') + 1);
        string studentID = line.substr(0, line.find(','));
        line = line.substr(line.find(',') + 1);
        string studentGrade = line.substr(0, line.find(')'));

        csg.emplace_back(courseName, studentID, studentGrade);
    }
    else if ("cdh(" == line.substr(0, 4)) {
        string courseName = line.substr(4, line.find(',') - 4);
        line = line.substr(line.find(',') + 1);
        string courseDay = line.substr(0, line.find(','));
        line = line.substr(line.find(',') + 1);
        string courseTime = line.substr(0, line.find(')'));

        cdh.emplace_back(courseName, courseDay, courseTime);
    }
    else if ("cr(" == line.substr(0, 3)) {
        string courseName = line.substr(3, line.find(',') - 3);
        line = line.substr(line.find(',') + 1);
        string courseRoom = line.substr(0, line.find(')'));

        cr.emplace_back(courseName, courseRoom);
    }
    else {
        out << endl << "**Error: ";
    }
    out << line << endl;
}