因此，我尝试选择 C++，为此我决定使用模板编写一个通用 Group 类，该类采用类型和大小作为模板参数：
在group.h中：
#ifndef __GROUP_H
#define __GROUP_H
#define MAX_SIZE 10
/**********************************************************
* Define a Group class that handles a collection of members
* of some Type
**********************************************************/
template <class Type, int max>
class Group {
private:
std::string name;
int count, size;
Type * members[max];
public:
Group();
Group(const std::string & _name);
~Group();
// display instance info
virtual void show();
// add member
void add_member(Type &);
// list memebers
void list();
// name setter/getter
void set_name(const std::string &);
const std::string & get_name();
};
#endif
组抄送：
/**********************************************************
* class methods for Group
**********************************************************/
template <class Type, int max>
Group<Type, max>::Group() : count(0), size(max), name("New Group") {};
template <class Type, int max>
Group<Type, max>::Group(const std::string & _name) : name(_name), count(0), size(max) {};
template <class Type, int max>
Group<Type, max>::~Group() {
int i = 0;
while(i < this->count) {
delete this->members[i];
++i;
}
}
template <class Type, int max>
void Group<Type, max>::show() {
std::cout << "<#Group - Name: " << this->name << ", Members: " << this->count << "/" << this->size << " >\n";
}
template <class Type, int max>
void Group<Type, max>::add_member(Type & member) {
if (this->count < this->size) {
this->members[this->count] = &member;
this->count++;
} else {
std::cout << "Error - this Group is full!\n";
}
}
template <class Type, int max>
void Group<Type, max>::list() {
int i = 0;
std::cout << "The following are members of the Group " << this->name <<":\n";
// assumes the member has a show() method implemented
while (i < this->count) {
std::cout << i << ". ";
(this->members[i])->show();
++i;
}
}
template <class Type, int max>
void Group<Type, max>::set_name(const std::string & _name) {
this->name = _name;
}
template <class Type, int max>
const std::string & Group<Type, max>::get_name() {
return this->name;
}
我还实现了一个 Person 类和一个 Employee 类（继承自 Person），它们都可以工作并具有 show() 方法。
我的主要看起来像这样：
test.cc
#include <iostream>
#include "group.h" // this also has the declarations and implementation for Person/Employee
int main (int argc, char const *argv[])
{
// Person ctor takes name and age
Person p1("John", 25);
Person p2("Jim", 29);
// Group takes name to init
Group <Person, 5> g("Ozcorp");
g.add_member(p1);
g.add_member(p2);
g.list();
}
我用一个简单的 Makefile 编译了它：
test: test.cc group.o
g++ -o test test.cc group.o
group.o: group.h group.cc
g++ -c group.cc
最后（哇），当我运行它时./test出现以下错误：
Undefined symbols:
"Group<Person, 5>::list()", referenced from:
_main in ccaLjrRC.o
"Group<Person, 5>::Group(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)", referenced from:
groups() in ccaLjrRC.o
_main in ccaLjrRC.o
"Group<Person, 5>::~Group()", referenced from:
groups() in ccaLjrRC.o
_main in ccaLjrRC.o
_main in ccaLjrRC.o
"Group<Person, 5>::add_member(Person&)", referenced from:
_main in ccaLjrRC.o
_main in ccaLjrRC.o
ld: symbol(s) not found
collect2: ld returned 1 exit status
make: *** [test] Error 1
如果你做到了这一点 - 谢谢 - 我希望能了解一些关于为什么会发生这种情况的见解。我试图尽可能多地分享代码（显然），所以如果太多了，请原谅我。源代码是在 mac osx 10.6.4 上使用 g++ 4.2.1 编译的。此外，任何风格/良好的编码习惯技巧都将受到赞赏。谢谢！
