纯虚函数是一种特殊的虚函数，在某些情况下，基类中不能对虚函数给出有意义的实现，把它声明为纯虚函数。
纯虚函数只有函数名、参数和返回值类型，没有函数体，具体实现留给该派生类去做。
语法：
virtual 返回值类型 函数名 (参数列表)=0;
纯虚函数在基类中为派生类保留一个函数的名字，以便派生类它进行重定义。如果在基类中没有保留函数名字，则无法支持多态性。
含有纯虚函数的类被称为抽象类，不能实例化对象，可以创建指针和引用。
派生类必须重定义抽象类中的纯虚函数，否则也属于抽象类。
基类中的纯虚析构函数也需要实现。
本文作者：jinganglang567
本文链接：https://www.cnblogs.com/tgfoven/p/17133050.html
版权声明：本作品采用知识共享署名-非商业性使用-禁止演绎 2.5 中国大陆许可协议进行许可。
作曲 : Steven D Cooper
Seems like nowadays, everybody lacks patience
Want it right now, always sick of this waiting
Hating on anyone, stuck in the process
For God sakes, how long will you waste, it's non sense
Telling you to give up on the dream, but who
Are they to throw away, all their faith in you
No way you're gonna fade, let them say and shoo
Get away, 'cause what they say don't have weight with you
You keep moving on, write that, do a song
Right track, you belong, fight back, prove them wrong
Yeah, just keep on, keeping on
Yeah, 'cause this track you be on
Right there's gotta lot of potential
So never give up, just sharpen your pencil
Close out all the negative talk
Put on those old shoes and choose where you walk
When you fall, stand up
And when you break, stand tough
And when they say, you can't
You say I can, I can
When you fall, stand up
And when you break, stand tough
And when they say, you can't
You say I can, I can
Don't lose faith, 'cause the minute you break
Is the minute you wake, with a million mistakes
And a million regrets that, you'll never get back
The time that you set back, to please other friends that
Tell you that you can't be what you wanna be
There's a world out there go and see what you wanna see
I've been there, I can relate
So let this song tell ya that it's never too late
Wide awake, and I see more than ever
That people are quick to give up on their endeavors
Never really try 'cause they're scared of failure
So, allow me to be the first to tell ya'
I've failed more times than I've succeeded
In the end, exactly what I needed
To allow me to learn the right steps
So I'd never go back, and I never regret
When you fall, stand up
And when you break, stand tough
And when they say, you can't
You say I can, I can
When you fall, stand up
And when you break, stand tough
And when they say, you can't
You say I can, I can
A lot of dreams get left at the wayside
And I can feel their death in the baseline
'Cause of something' someone once said
At once dead,
Don't let them stop you in your tracks, at once dead
Say to yourself, I'ma be stronger than
Stay up late everyday working harder than
Keep my head focused, stick to the plan
They say I can't but I say I can
When you fall, stand up
And when you break, stand tough
And when they say, you can't
You say I can, I can
When you fall, stand up
And when you break, stand tough
And when they say, you can't
You say I can, I can
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