0x01 实现模板类
通常在C/C++中实现一个类，都是将声明放在.h文件中，将定义（实现）放在.c或者.cpp文件中，例如：
通常示例多文件编译
myClass.h
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| #ifndef MY_CLASS_H
#define MY_CLASS_H
class myClass {
public:
myClass();
...
private:
...
}
#endif
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myClass.cpp
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| #include "myClass.h"
myClass::myClass() {
...
}
...
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myClass.main.cpp
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| #include "myClass.h"
int main()
{
myClass mClass();
...
return 0;
}
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然后编译的时候直接运行makefile或者执行命令：
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| g++ -c myClass.cpp
g++ -c myClass.main.cpp
g++ myClass.o myClass.main.o -o main
./main
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就可以运行了。这在没有设计模板类的时候一切都会很顺利，但是只要涉及到了模板类就…
模板类多文件遇到的问题
就拿一个循环队列来举例子吧。
cycleQueue.hpp
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| #ifndef CYCLE_QUEUE_HPP
#define CYCLE_QUEUE_HPP
#include <exception>
template<class T>
class cycleQueue
{
private:
unsigned int size;
unsigned int front;
unsigned int tail;
T* data;
public:
cycleQueue(unsigned int nsize);
...
int length();
};
#endif
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cycleQueue.cpp
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| #include "cycleQueue.hpp"
template<class T>
cycleQueue<T>::cycleQueue(unsigned int nsize)
:size(nsize + 1),
front(0),
tail(0)
{
...
template<class T>
int cycleQueue<T>::length()
{
int len = (int)tail - (int)front;
return len >= 0 ? len : -len;
}
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cycleQueue.main.cpp
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| #include <iostream>
using namespace std;
#include "cycleQueue.hpp"
int main()
{
cycleQueue<int> queue(5);
...
return 0;
}
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按照常理，正常使用g++编译即可生成main可执行文件，但是在执行最后一步链接的时候会出现问题。
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| $ g++ -c cycleQueue.cpp
$ g++ -c cycleQueue.main.cpp
$ g++ cycleQueue.o cycleQueue.main.o -o main
Undefined symbols for architecture x86_64:
"cycleQueue<int>::isFull()", referenced from:
_main in cycleQueue.main.o
"cycleQueue<int>::length()", referenced from:
_main in cycleQueue.main.o
"cycleQueue<int>::deQueue()", referenced from:
_main in cycleQueue.main.o
"cycleQueue<int>::enQueue(int)", referenced from:
_main in cycleQueue.main.o
"cycleQueue<int>::isEmpty()", referenced from:
_main in cycleQueue.main.o
"cycleQueue<int>::cycleQueue(unsigned int)", referenced from:
_main in cycleQueue.main.o
"cycleQueue<int>::~cycleQueue()", referenced from:
_main in cycleQueue.main.o
ld: symbol(s) not found for architecture x86_64
collect2: error: ld returned 1 exit status
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可以看到，单独编译实现代码的时候是可以通过的，但是在两个文件链接起来的时候出现了问题。经过查找资料，貌似是因为实现文件中实现的是cycleQueue<T>这个类型，但是main中使用了cycleQueue<int>这个类型，所以编译器找不到这个类型的定义。
想了想，这好办啊，只要把实现的定义也加进去就好了呀。
于是乎，cycleQueue.hpp就成了：
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| #ifndef CYCLE_QUEUE_HPP
#define CYCLE_QUEUE_HPP
#include <exception>
template<class T>
class cycleQueue
{
...
};
#include "cycleQueue.cpp"
#endif
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而为了解决include重复问题，cycleQueue.cpp也变成了：
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| #ifndef CYCLE_QUEUE_CPP
#define CYCLE_QUEUE_CPP
#include "cycleQueue.hpp"
...
#endif
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于是乎，搭配makefile就可以快速实现编译了
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| cycleQueue: cycleQueue.o cycleQueue.main.o
g++ cycleQueue.o cycleQueue.main.o -o cycleQueue
make clean
cycleQueue.o: cycleQueue.cpp
g++ -c cycleQueue.cpp
cycleQueue.main.o: cycleQueue.main.cpp
g++ -c cycleQueue.main.cpp
clean:
rm *.o
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| $ ls -la
total 32
drwxr-xr-x 6 chenke staff 192 Sep 7 13:50 .
drwxr-xr-x 3 chenke staff 96 Sep 7 14:10 ..
-rw-r--r-- 1 chenke staff 956 Sep 7 13:40 cycleQueue.cpp
-rw-r--r-- 1 chenke staff 403 Sep 7 13:32 cycleQueue.hpp
-rw-r--r-- 1 chenke staff 695 Sep 7 13:43 cycleQueue.main.cpp
-rw-r--r-- 1 chenke staff 242 Sep 7 13:01 makefile
$ make
g++ -c cycleQueue.cpp
g++ -c cycleQueue.main.cpp
g++ cycleQueue.o cycleQueue.main.o -o cycleQueue
make clean
rm *.o
$ ls -la
total 80
drwxr-xr-x 7 chenke staff 224 Sep 7 14:12 .
drwxr-xr-x 3 chenke staff 96 Sep 7 14:10 ..
-rwxr-xr-x 1 chenke staff 20512 Sep 7 14:12 cycleQueue
-rw-r--r-- 1 chenke staff 956 Sep 7 13:40 cycleQueue.cpp
-rw-r--r-- 1 chenke staff 403 Sep 7 13:32 cycleQueue.hpp
-rw-r--r-- 1 chenke staff 695 Sep 7 13:43 cycleQueue.main.cpp
-rw-r--r-- 1 chenke staff 242 Sep 7 13:01 makefile
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一顿操作猛如虎23333
