C++核心準(zhǔn)則編譯邊學(xué)-F.22 使用T*或onwer指明唯一對(duì)象

F.22: Use T* or owner to designate a single object（使用T*或owner指明唯一對(duì)象）

Reason（原因）

Readability: it makes the meaning of a plain pointer clear. Enables significant tool support.

可讀性：這可以讓裸指針的含義更明確。使重要的工具支持有效。

譯者注

譯者注：owner是gsl（準(zhǔn)則支持庫(kù)）提供的一個(gè)功能，從編譯的角度來(lái)看和T*的含義一致，但是附加了所有權(quán)語(yǔ)義，可以幫助程序員理解代碼和工具檢查。

Note（注意）

In traditional C and C++ code, plain T* is used for many weakly-related purposes, such as:

在傳統(tǒng)的C和C++代碼中，裸指針用于很多沒有什么關(guān)系的目的，例如：

• Identify a (single) object (not to be deleted by this function)

  表示一個(gè)（單一）對(duì)象（不會(huì)被本函數(shù)刪除）
  

• Point to an object allocated on the free store (and delete it later)

  指向一個(gè)從自由存儲(chǔ)上獲取的對(duì)象（以后會(huì)刪除）
  

• Hold the nullptr

  持有nullptr
  

• Identify a C-style string (zero-terminated array of characters)

  表示一個(gè)C風(fēng)格字符串（以0結(jié)尾的字符數(shù)組）
  

• Identify an array with a length specified separately

  表示一個(gè)數(shù)組，長(zhǎng)度被另外定義
  

• Identify a location in an array

  表示數(shù)組的首地址
  

This makes it hard to understand what the code does and is supposed to do. It complicates checking and tool support.

這樣做的結(jié)果是很難理解代碼在做什么和被預(yù)期做什么。無(wú)論是檢查還是工具支持都會(huì)復(fù)雜。

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}

譯者注：這可能是我們每天都能見到的指針用法，很難看出它們到底是前面提供的那種用法。

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表現(xiàn)所有權(quán)，zstring表達(dá)C風(fēng)格的字符串

Also: Assume that a T* obtained from a smart pointer to T (e.g., unique_ptr) points to a single element.

參考：假定T*是從指向T的智能指針（例如unique_prt）獲取，指向單一對(duì)象的指針。

See also: Support library

參考：支持庫(kù)。

See also: Do not pass an array as a single pointer

參考：不要使用單一指針傳遞數(shù)組

Enforcement（實(shí)施建議）

• (Simple) ((Bounds)) Warn for any arithmetic operation on an expression of pointer type that results in a value of pointer type.

  (簡(jiǎn)單）((邊界))警告所有針對(duì)指針表達(dá)式，并得到指針類型結(jié)果的算數(shù)操作。