C++核心准则编译边学-F.22 使用T*或onwer指明唯一对象
F.22: Use T*
or owner
to designate a single object(使用T*或owner指明唯一对象)
Reason(原因)
Readability: it makes the meaning of a plain pointer clear. Enables significant tool support.
可读性:这可以让裸指针的含义更明确。使重要的工具支持有效。
译者注
译者注:owner
Note(注意)
In traditional C and C++ code, plain T*
is used for many weakly-related purposes, such as:
在传统的C和C++代码中,裸指针用于很多没有什么关系的目的,例如:
Identify a (single) object (not to be deleted by this function)
表示一个(单一)对象(不会被本函数删除)
Point to an object allocated on the free store (and delete it later)
指向一个从自由存储上获取的对象(以后会删除)
Hold the
nullptr
持有nullptr
Identify a C-style string (zero-terminated array of characters)
表示一个C风格字符串(以0结尾的字符数组)
Identify an array with a length specified separately
表示一个数组,长度被另外定义
Identify a location in an array
表示数组的首地址
This makes it hard to understand what the code does and is supposed to do. It complicates checking and tool support.
这样做的结果是很难理解代码在做什么和被预期做什么。无论是检查还是工具支持都会复杂。
Example(示例)
void use(int* p, int n, char* s, int* q)
{
p[n - 1] = 666; // Bad: we don't know if p points to n elements;
// assume it does not or use span
cout << s; // Bad: we don't know if that s points to a zero-terminated array of char;
// assume it does not or use zstring
delete q; // Bad: we don't know if *q is allocated on the free store;
// assume it does not or use owner
}
译者注:这可能是我们每天都能见到的指针用法,很难看出它们到底是前面提供的那种用法。
better(稍好)
void use2(span<int> p, zstring s, owner<int*> q)
{
p[p.size() - 1] = 666; // OK, a range error can be caught
cout << s; // OK
delete q; // OK
}
Note(注意)
owner
represents ownership, zstring
represents a C-style string.
owner
Also: Assume that a T*
obtained from a smart pointer to T
(e.g., unique_ptr
) points to a single element.
参考:假定T*是从指向T的智能指针(例如unique_prt
See also: Support library
参考:支持库。
See also: Do not pass an array as a single pointer
参考:不要使用单一指针传递数组
Enforcement(实施建议)
(Simple) ((Bounds)) Warn for any arithmetic operation on an expression of pointer type that results in a value of pointer type.
(简单)((边界))警告所有针对指针表达式,并得到指针类型结果的算数操作。