c++ - QString 和 stdstring 组合在 std::stringstream 中不起作用 - 编译错误

Question

```

#include <iostream>
#include <sstream>
#include <QString>
class Printer {
public:
    inline std::ostream& operator<<(const std::string& str) {
    stream << str;
    return stream;
    }
    inline std::ostream& operator<<(int numb) {
    stream << numb;
    return stream;
    }
    inline std::ostream& operator<<(const QString& str) {
    stream << str.toStdString();
    return stream;
    }
    virtual ~Printer(void) {
    std::cout << stream.str();
    }

private:
    std::stringstream stream;
};

int main(void)
{
    QString qstring("qstring");
    std::string stdstring("std::string");

    Printer() << qstring << stdstring << 1;   // Works like charm
    Printer() << stdstring << qstring << 1;   // Doesnt work :(

    return 0;
}

```

任何人都可以看看上面的代码并告诉我我有评论的主要方法中的问题是什么

Answer 1

对于您的原始代码

Printer() << stdstring << qstring

等于

(Printer().operator<<(stdstring)).operator<<(qstring)

你可以在这里看到问题，

Printer() << stdstring

将返回一个ostream &，你将QString传递给ostream。我认为您应该返回流以外的 Printer。

class Printer {
public:

    virtual ~Printer(void) {
        std::cout << o.str();
    }

    std::stringstream o;
};

Printer &operator<<(Printer &p, const std::string &s)
{
    p.o << s;
    return p;
}

Printer &operator<<(Printer &p, const QString &s)
{
    p.o << s.toStdString();
    return p;
}

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    QString qstring("qstring");
    std::string stdstring("std::string");
    Printer p;

    p << stdstring << qstring;

    return a.exec();
}