c++ - 为什么编译器无法在 .cpp 文件中找到方法定义

Question

我有一个用于声明该类的头文件，一个用于其方法定义的 cpp 文件和一个主源文件，主要是我包含了头文件，但编译器提示我没有定义他的方法。 ..日期.h

    #ifndef _DATE_
#define _DATE_
#include <iostream>
#include <exception>
#include <string>

using namespace std;
class date{
    int day, month, year;
public:
    date(int d, int m, int y) :day(d), month(m), year(y){}
    int getDay() const{ return day; }
    int getMonth() const { return month; }
    int getYear() const { return year; }
    bool operator==(const date& d) const{ return ((day == d.day) && (month == d.month) && (year == d.year)); }
    bool operator>(const date& d) const;
    bool operator<(const date& d) const { return !(*this>d || *this == d); }
    ostream& print(ostream& os) const;
};


#endif

日期.cpp

#include "Date.h"

bool date::operator>(const date& d) const {
    if (year > d.year)  return true;
    if (year < d.year)  return false;
    if (month>d.month)  return true;
    if (month < d.month)    return false;
    if (day>d.day)  return true;
    return false;
}

ostream& date::print(ostream& out) const    {
    if (day < 10)   out << "0";
    out << day << "/";
    if (month < 10) out << "0";
    out << month << "/";
    out << year << endl;
    return out;
}



ostream& operator<<(ostream& ot, const date& d) {
    return d.print(ot);
}

主要.cpp

#include "Date.h"

int main()  {
    date d(17, 10, 1996);
    cout << d;
    return 0;
}

错误:错误 1 ​​error C2679: binary '<<' : no operator found which takes a right-hand operand of type 'date' (or there is no acceptable conversion) c:\users\aub\documents\visual studio 2013\projects\project22\project22\main.cpp 5

2   IntelliSense: no operator "<<" matches these operands
        operand types are: std::ostream << date c:\Users\aub\Documents\Visual Studio 2013\Projects\Project22\Project22\main.cpp 5

我也尝试过在 date.h 中实现我的重载运算符<<，但没有成功...

我在头文件中声明 operator<< 后得到的错误是:错误1 error LNK2005: "class std::basic_ostream > & __cdecl operator<<(class std::basic_ostream > &,class date const &)"(??6@YAAAV?$basic_ostream@DU?$char_traits@D@std @@@std@@AAV01@ABVdate@@@Z) 已经定义在Date.obj c:\Users\aub\documents\visual studio 2013\Projects\Project22\Project22\main.obj

错误 2 错误 LNK1169:找到一个或多个多次定义的符号 c:\users\aub\documents\visual studio 2013\Projects\Project22\Debug\Project22.exe 1

Answer 1

声明ostream& operator<<(ostream& ot, const date& d);应该在标题中。