Question

所以我想编写一个可以像这样使用的缩进输出类：

Debug f;
f.open("test.txt");
f << Debug::IndS << "Start" << std::endl;
f << Debug::Ind << "test" << std::endl;
f << Debug::IndE << "End" << std::endl;

将输出：

Start
    test
End

因此IndS将打印出当前缩进并增加缩进，Ind将打印出当前缩进，IndE将减少缩进并打印出当前缩进。我试图像这样创建它：

class Debug : public std::ofstream {
    public:
        Debug();
        ~Debug();

    private:
        std::string IndentText;
        int _Indent;

    public:
        void SetIndentText(const char* Text);
        inline void Indent(int Amount);
        inline void SetIndent(int Amount);

        inline std::ofstream& Ind (std::ofstream& ofs);
        inline std::ofstream& IndS(std::ofstream& ofs);
        inline std::ofstream& IndE(std::ofstream& ofs);
};

Debug::Debug () : std::ofstream() {
    IndentText = "    ";
}

Debug::~Debug () {
}

void Debug::SetIndentText (const char* Text) {
    IndentText = Text;
}

void Debug::Indent (int Amount) {
    _Indent += Amount;
}

void Debug::SetIndent(int Amount) {
    _Indent = Amount;
}

std::ofstream& Debug::Ind (std::ofstream& ofs) {
    for (int i = 0;i < _Indent;i++) {
        ofs << IndentText;
    }
    return ofs;
}

std::ofstream& Debug::IndS (std::ofstream& ofs) {
    ofs << Ind;
    _Indent++;
    return ofs;
}

std::ofstream& Debug::IndE (std::ofstream& ofs) {
    _Indent--;
    ofs << Ind;
    return ofs;
}

所以我认为这有一些问题：

它无法编译。 no match for 'operator<<' (operand types are 'std::ofstream {aka std::basic_ofstream<char>}' and '<unresolved overloaded function type>') ofs << Ind; candidates are:的错误等等等等
我没有覆盖所有构造函数。有没有办法做到这一点？我想我只需重写所有构造函数来执行IndentText = " ";并委托重载的构造函数

有人可以帮我吗？谢谢！

Answer 1

您通常不应继承std::ostream或其实施，例如std::ofstream。将它们包装到另一个类中。

以下是评论中提到的我的想法的简短草图

#include <iostream>
#include <fstream>

using namespace std;

class Logger {
public:
    Logger(ostream& os) : os_(os), curIndentLevel_(0) {}
    void increaseLevel() { ++curIndentLevel_; }
    void decreaseLevel() { --curIndentLevel_; }

private:
    template<typename T> friend ostream& operator<<(Logger&, T);

    ostream& os_;
    int curIndentLevel_;
};

template<typename T> 
ostream& operator<<(Logger& log, T op) {
    for(int i = 0; i < log.curIndentLevel_ * 4; ++i) {
        log.os_ << ' ';
    }
    log.os_ << op;
    return log.os_;
}

int main() {
    Logger log(cout);
    log.increaseLevel();
    log << "Hello World!" << endl;
    log.decreaseLevel();
    log << "Hello World!" << endl;
    return 0;
}

输出

    Hello World!
Hello World!

Live Sample

这是一个小变体，展示了如何使用operator<<()重载来快速编码：

class Logger {
public:
    Logger(ostream& os) : os_(os), curIndentLevel_(0) {}
    Logger& increaseLevel() { ++curIndentLevel_; return *this; }
    Logger& decreaseLevel() { --curIndentLevel_; return *this; }

    // ... as before ...        
};

int main() {
    Logger log(cout);

    log.increaseLevel() << "Hello World!" << endl;
    log.decreaseLevel() << "Hello World!" << endl;
    return 0;
}

Live Sample

您可以采用相同的方式提供额外的I / O操纵器样式免费功能。

Answer 2

替代解决方案：

#include <iostream>
#include <fstream>

class IndentClass {
    public:
        IndentClass();
        ~IndentClass();

    private:
        std::string IndentText;
        int _Indent;

    public:
        inline void SetIndentText(const char* Text);
        inline void Indent(int Amount);
        inline void SetIndent(int Amount);

        inline void ind (std::ostream& ofs);

        class Ind_t {
            public:
                IndentClass& state;
                Ind_t (IndentClass& _state) : state(_state) {}
                friend inline std::ostream& operator<< (std::ostream& ofs, Ind_t& ind);
        };
        class IndS_t {
            public:
                IndentClass& state;
                IndS_t (IndentClass& _state) : state(_state) {}
                friend inline std::ostream& operator<< (std::ostream& ofs, IndS_t& ind);
        };
        class IndE_t {
            public:
                IndentClass& state;
                IndE_t (IndentClass& _state) : state(_state) {}
                friend inline std::ostream& operator<< (std::ostream& ofs, IndE_t& ind);
        };
        Ind_t Ind;
        IndS_t IndS;
        IndE_t IndE;
};

IndentClass::IndentClass () : IndentText("    "), _Indent(0), Ind(*this), IndS(*this), IndE(*this) {

}

IndentClass::~IndentClass () {
}

void IndentClass::SetIndentText (const char* Text) {
    IndentText = Text;
}

void IndentClass::Indent (int Amount) {
    _Indent += Amount;
}

void IndentClass::SetIndent(int Amount) {
    _Indent = Amount;
}

void IndentClass::ind (std::ostream& ofs) {
    for (int i = 0;i < _Indent;i++) {
        ofs << IndentText;
    }
}

std::ostream& operator<< (std::ostream& ofs, IndentClass::Ind_t& ind) {
    ind.state.ind(ofs);
    return ofs;
}

std::ostream& operator<< (std::ostream& ofs, IndentClass::IndS_t& inds) {
    inds.state.ind(ofs);
    inds.state.Indent(1);
    return ofs;
}

std::ostream& operator<< (std::ostream& ofs, IndentClass::IndE_t& inde) {
    inde.state.Indent(-1);
    inde.state.ind(ofs);
    return ofs;
}

int main () {
    IndentClass i;

    std::cout << i.IndS << "test" << std::endl;
    std::cout << i.Ind << "test" << std::endl;
    std::cout << i.IndE << "test" << std::endl;

    return 0;
}

Ideone Example

C ++缩进输出类继承ofstream

2 个答案: