“std::operator”中的“operator<<”不匹配

Question

我是 C++ 新手。我在这里尝试了我的第一个程序。在我看来，这个程序是正确的。

#include <iostream>

using namespace std;

class mystruct
{
    private:
        int m_a;
        float m_b;

    public:
        mystruct(int x, float y)
        {
                m_a = x;
                m_b = y;
        }

};


int main()
{

        mystruct m = mystruct(5,3.14);

        cout << "my structure " << m << endl;

        return 0;
}

但是我收到了很多错误。不知道为什么？

cout.cpp: In function ‘int main()’:
cout.cpp:26:29: error: no match for ‘operator<<’ in ‘std::operator<< [with _Traits = std::char_traits<char>]((* & std::cout), ((const char*)"my structure ")) << m’
cout.cpp:26:29: note: candidates are:
/usr/include/c++/4.6/ostream:110:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__ostream_type& (*)(std::basic_ostream<_CharT, _Traits>::__ostream_type&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.6/ostream:110:7: note:   no known conversion for argument 1 from ‘mystruct’ to ‘std::basic_ostream<char>::__ostream_type& (*)(std::basic_ostream<char>::__ostream_type&) {aka std::basic_ostream<char>& (*)(std::basic_ostream<char>&)}’
/usr/include/c++/4.6/ostream:119:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__ios_type& (*)(std::basic_ostream<_CharT, _Traits>::__ios_type&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>, std::basic_ostream<_CharT, _Traits>::__ios_type = std::basic_ios<char>]
/usr/include/c++/4.6/ostream:119:7: note:   no known conversion for argument 1 from ‘mystruct’ to ‘std::basic_ostream<char>::__ios_type& (*)(std::basic_ostream<char>::__ios_type&) {aka std::basic_ios<char>& (*)(std::basic_ios<char>&)}’
/usr/include/c++/4.6/ostream:129:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(std::ios_base& (*)(std::ios_base&)) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.6/ostream:129:7: note:   no known conversion for argument 1 from ‘mystruct’ to ‘std::ios_base& (*)(std::ios_base&)’
/usr/include/c++/4.6/ostream:167:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.6/ostream:167:7: note:   no known conversion for argument 1 from ‘mystruct’ to ‘long int’
/usr/include/c++/4.6/ostream:171:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long unsigned int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.6/ostream:171:7: note:   no known conversion for argument 1 from ‘mystruct’ to ‘long unsigned int’
/usr/include/c++/4.6/ostream:175:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(bool) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.6/ostream:175:7: note:   no known conversion for argument 1 from ‘mystruct’ to ‘bool’
/usr/include/c++/4.6/bits/ostream.tcc:93:5: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.6/bits/ostream.tcc:93:5: note:   no known conversion for argument 1 from ‘mystruct’ to ‘short int’
/usr/include/c++/4.6/ostream:182:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(short unsigned int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.6/ostream:182:7: note:   no known conversion for argument 1 from ‘mystruct’ to ‘short unsigned int’
/usr/include/c++/4.6/bits/ostream.tcc:107:5: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/include/c++/4.6/bits/ostream.tcc:107:5: note:   no known conversion for argument 1 from ‘mystruct’ to ‘int’
/usr/include/c++/4.6/ostream:193:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(unsigned int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.6/ostream:193:7: note:   no known conversion for argument 1 from ‘mystruct’ to ‘unsigned int’
/usr/include/c++/4.6/ostream:202:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.6/ostream:202:7: note:   no known conversion for argument 1 from ‘mystruct’ to ‘long long int’
/usr/include/c++/4.6/ostream:206:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long long unsigned int) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.6/ostream:206:7: note:   no known conversion for argument 1 from ‘mystruct’ to ‘long long unsigned int’
/usr/include/c++/4.6/ostream:211:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(double) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.6/ostream:211:7: note:   no known conversion for argument 1 from ‘mystruct’ to ‘double’
/usr/include/c++/4.6/ostream:215:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(float) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.6/ostream:215:7: note:   no known conversion for argument 1 from ‘mystruct’ to ‘float’
/usr/include/c++/4.6/ostream:223:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(long double) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.6/ostream:223:7: note:   no known conversion for argument 1 from ‘mystruct’ to ‘long double’
/usr/include/c++/4.6/ostream:227:7: note: std::basic_ostream<_CharT, _Traits>::__ostream_type& std::basic_ostream<_CharT, _Traits>::operator<<(const void*) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__ostream_type = std::basic_ostream<char>]
/usr/include/c++/4.6/ostream:227:7: note:   no known conversion for argument 1 from ‘mystruct’ to ‘const void*’
/usr/include/c++/4.6/bits/ostream.tcc:121:5: note: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>::__streambuf_type*) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_ostream<_CharT, _Traits>::__streambuf_type = std::basic_streambuf<char>]
/usr/include/c++/4.6/bits/ostream.tcc:121:5: note:   no known conversion for argument 1 from ‘mystruct’ to ‘std::basic_ostream<char>::__streambuf_type* {aka std::basic_streambuf<char>*}’
/usr/include/c++/4.6/bits/basic_string.h:2693:5: note: template<class _CharT, class _Traits, class _Alloc> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const std::basic_string<_CharT, _Traits, _Alloc>&)
/usr/include/c++/4.6/ostream:451:5: note: template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, _CharT)
/usr/include/c++/4.6/ostream:456:5: note: template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, char)
/usr/include/c++/4.6/ostream:462:5: note: template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, char)
/usr/include/c++/4.6/ostream:468:5: note: template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, signed char)
/usr/include/c++/4.6/ostream:473:5: note: template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, unsigned char)
/usr/include/c++/4.6/ostream:493:5: note: template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const _CharT*)
/usr/include/c++/4.6/bits/ostream.tcc:323:5: note: template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(std::basic_ostream<_CharT, _Traits>&, const char*)
/usr/include/c++/4.6/ostream:510:5: note: template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const char*)
/usr/include/c++/4.6/ostream:523:5: note: template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const signed char*)
/usr/include/c++/4.6/ostream:528:5: note: template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, const unsigned char*)

Answer 1

你需要为mystruct类重载operator <<

就像是 ：-

friend ostream& operator << (ostream& os, const mystruct& m)
{
    os << m.m_a <<" " << m.m_b << endl;
    return os ;
}

看到这里

Answer 2

只有一个错误：

cout.cpp：26：29：错误：'std :: operator <<中没有匹配'operator <<'[与_Traits = std :: char_traits]（（*＆std :: cout），（（const char *） ）“我的结构”））<< m'

这意味着编译器无法为operator<<找到匹配的重载。 输出的其余部分是编译器列出operator<<不匹配的重载。 第三行实际上是这样说的：

cout.cpp：26：29：注意：候选人是：

Answer 3

显然，标准库提供的操作员不知道如何处理用户定义的类型mystruct 。 它仅适用于预定义的数据类型。 为了能够将它用于您自己的数据类型，您需要重载operator <<以获取用户定义的数据类型。

Answer 4

Object是方法和变量的集合。您不能通过cout操作在对象中打印变量。 如果要显示对象内部的内容，则必须在类中声明getter或display text方法。

前

#include <iostream>

using namespace std;

class mystruct

{
private:
    int m_a;
    float m_b;

public:
    mystruct(int x, float y)
    {
            m_a = x;
            m_b = y;
    }
    public:
    void getm_aAndm_b()
    {
        cout<<m_a<<endl;
        cout<<m_b<<endl;
    }



};

int main()
{

    mystruct m = mystruct(5,3.14);

    cout << "my structure " << endl;
    m.getm_aAndm_b();
    return 0;

}

并不是说这只是一种做法

Answer 5

你可以得到：

#include <iostream>

using namespace std;

class Mystruct
{
    private:
        int m_a;
        float m_b;

    public:
        //get the value
        int m_getA() {return m_a;} //get the value m_a
        float m_getB() {return m_b;} //get the value m_b

        //set
        void mystruct(int x, float y)
        {
            m_a = x; //set m_a
            m_b = y; //set m_b
        }
};


int main()
{

        Mystruct m;
        m.mystruct(5, 3.14);

        cout << "my structure m(" 
             << m.m_getA() << ","  //use the method to get m_a
             << m.m_getB() << ")"  //use the method to get m_b
             << endl;

        return 0;
}

Answer 6

我认为您需要创建一个目标文件并使用它来获得结果

#include <iostream>

using namespace std;

class Mystruct
{
    private:
        int m_a;
        float m_b;

    public:
        mystruct(int x, float y)
        {
                m_a = x;
                m_b = y;
        }

};


int main()
{
    Mystruct objectname; //creating the object file of the class;
    float variable = objectname.mystruct(5,3.14);

    cout << "my structure " << variable << endl;

    return 0;
}