使用模板类时，除main.cpp之外似乎不包含任何cpp文件

Question

I decided to cut the necessary code down to the bare minimum needed to display this error. I have an STL list wrapper template class that exists in hc_list.h file. The entire code is below:

// hc_list.h file
#ifndef HC_LIST_H
#define HC_LIST_H

#include <cstdlib>
#include <list>

template <typename T>
class hcList
{
    private:
    std::list<T> selfList ; // a single internal STL list to hold the values

    public:
    hcList(void) {} ;
    ~hcList(void){} ;
    // The error occurs on the line below
    template <typename U> friend std::ostream& operator<<(std::ostream &, const hcList<U> &) ;
} ;
#endif // HC_LIST_H

This code is included in the main.cpp file, where the main function is below:

// main.cpp file
#include <iostream>
#include "hc_list.h"
int main()
{
    std::cout << "Begin Test" << std::endl;
    return 0;
}

This code, when entered into a CodeBlocks project will compile as is with 0 errors or warnings. However, then I include another cpp file and attempt to include the list header, like the following:

// anyNamedFile.cpp file
#include "hc_list.h"

When I include any cpp file into the project, I get a compiler error:

error: expected initializer before '&' token

I do not understand what I am doing wrong, and could really use some help.

Answer 1

Your header file uses std::ostream , (just before an & ) but does not include any header which might declare it.

Try adding

#include <iosfwd>

in your header.