你不能像普通函数一样(在 '.hpp' 文件中声明，'.cpp' 文件中的定义).有几种方法可以解决这个问题.

You are not allowed to seperate the declaration and definition of a templated function in the same way that you would a normal function (declaration in '.hpp' file, definition in '.cpp' file). There are a couple of ways you can get around that.

您可以在头文件的同一位置声明和定义函数.

You can declare AND define the function in the same place in the header file.

或

您可以在名为 functions.inl 的文件中尝试此操作:

You could try this, in a file called functions.inl:

template<typename T> 
inline string vector_tostr(std::vector<T> v){
    std::stringstream ss;
    std::string thestring = "";
    if(v.size() > 0){
        ss << "[";
        for(size_t i = 0; i < v.size(); i++){
            if(i != 0)
                ss << " ";
            ss << v[i];
        }
        ss << "]";
        thestring = ss.str();
    }
    return thestring;
}

然后，在头文件(functions.hpp)的末尾，输入:

Then, at the end of the header file (functions.hpp), type this in:

#include "functions.inl"

.inl 是内联头文件的文件扩展名.您可以使用它来分隔声明以及模板化函数的定义.

.inl is the file extension for the inline header file. You can use this to seperate the declaration and definition of templated functions.