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update 练习12.17 #52

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update 练习12.17 #52

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9 changes: 5 additions & 4 deletions ch12/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -141,13 +141,14 @@ typedef unique_ptr<int> IntP;
(e) IntP p4(new int(2048));
(f) IntP p5(p2.get());
```

注：“合法”意味着编译可以通过，但不代表不会产生错误！
* (a) 不合法。在定义一个 unique_ptr 时，需要将其绑定到一个new 返回的指针上。
* (b) 合法。但是可能会有后续的程序错误。当 p1 被释放时，p1 所指向的对象也被释放，所以导致 pi 成为一个空悬指针。
编译时报错: invalid conversion from 'int' to 'std::unique_ptr<int>::pointer { aka int* }' [-fpermissive]
* (b) 合法。但是可能会有后续的程序错误。当 p1 被释放时，其实际所指向的对象 —— ix 也会被释放，但是 ix 并非通过 new 创建，所以此时操作系统会报错。
* (c) 合法。但是也可能会使得 pi2 成为空悬指针。
* (d) 不合法。当 p3 被销毁时，它试图释放一个栈空间的对象。
* (d) 合法。但是当 p3 被销毁时，它试图释放一个栈空间的对象。
* (e) 合法。
* (f) 不合法。p5 和 p2 指向同一个对象，当 p5 和 p2 被销毁时，会使得同一个指针被释放两次。
* (f) 合法。但是p5 和 p2 指向同一个对象，当 p5 和 p2 被销毁时，会使得同一个指针被释放两次。

## 练习12.18

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