＆＃34;标识符未定义＆＃34;模板类成员函数中的错误

Question

我想创建一个复杂的＆＃39;模板类执行复数计算。但是当我创建一个成员函数时，编译器会抛出一个＆＃34;标识符未定义＆＃34;我尝试调用该函数时出错。

#include <iostream>
template <class T>
class complex {
private:
    T rl, im;
public:
    complex() : rl(0), im(0) {}
    complex(T x, T y) : rl(x), im(y) {}
    void read();
    complex<T> conjugate (const complex<T>& param);     
};
template <class T>
void complex<T>::read() {
    std::cout << "Enter the real no. and the imaginery part: " << std::endl;
    std::cin >> rl >> im;
}
template< class T >
complex<T> complex<T>::conjugate(const complex<T>& param) {
    complex temp;
    temp.rl = param.rl;
    temp.im = -param.im;
    return temp;
}

主要功能看起来像

#include <iostream>
#include "complex.h"
int main() {
complex<int> ob1(4, 5);
complex<int> result;
result = conjugate(ob1); //not able to call conjugate, "identifier is undefined" error
result.display();
return 0;
}