對於單行if或循環使用大括號（即{}）的目的是什麼？

本文翻譯自：What's the purpose of using braces (i.e. {}) for a single-line if or loop?

I'm reading some lecture notes of my C++ lecturer and he wrote the following: 我正在閱讀我的C ++講師的一些講義，他寫了以下內容：

1. Use Indentation // OK 使用縮進//確定
2. Never rely on operator precedence - Always use parentheses // OK 永遠不要依賴運算符優先級 - 始終使用括號//確定
3. Always use a { } block - even for a single line // not OK , why ??? 總是使用{}塊 - 即使是單行// 不行 ，爲什麼???
4. Const object on left side of comparison // OK 比較左側的Const對象// OK
5. Use unsigned for variables that are >= 0 // nice trick 對於> = 0 //好玩法的變量使用無符號
6. Set Pointer to NULL after deletion - Double delete protection // not bad 刪除後將指針設置爲NULL - 雙刪除保護//不錯

The 3rd technique is not clear to me: what would I gain by placing one line in a { ... } ? 第三種技術對我來說並不清楚：在{ ... }放置一行會獲得什麼？

For example, take this weird code: 例如，拿這個奇怪的代碼：

int j = 0;
for (int i = 0 ; i < 100 ; ++i)
{
    if (i % 2 == 0)
    {
        j++;
    }
}

and replace it with: 並替換爲：

int j = 0;
for (int i = 0 ; i < 100 ; ++i)
    if (i % 2 == 0)
        j++;

What's the benefit of using the 1st version? 使用第一個版本有什麼好處？

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#1樓

參考：https://stackoom.com/question/pA02/對於單行if或循環使用大括號-即-的目的是什麼

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#2樓

Let's attempt to also modify i when we increment j : 當我們遞增j時，讓我們嘗試修改i ：

int j = 0;
for (int i = 0 ; i < 100 ; ++i)
    if (i % 2 == 0)
        j++;
        i++;

Oh no! 不好了！ Coming from Python, this looks ok, but in fact it isn't, as it's equivalent to: 來自Python，這看起來不錯，但實際上並非如此，因爲它相當於：

int j = 0;
for (int i = 0 ; i < 100 ; ++i)
    if (i % 2 == 0)
        j++;
i++;

Of course, this is a silly mistake, but one that even an experienced programmer could make. 當然，這是一個愚蠢的錯誤，但即使是經驗豐富的程序員也可以做到。

Another very good reason is pointed out in ta.speot.is's answer . 在ta.speot.is的回答中指出了另一個很好的理由 。

A third one I can think of is nested if 's: 我能想到的第三個是嵌套if ：

if (cond1)
   if (cond2) 
      doSomething();

Now, assume you now want to doSomethingElse() when cond1 is not met (new feature). 現在，假設您現在想要在cond1時cond1 doSomethingElse() （新功能）。 So: 所以：

if (cond1)
   if (cond2) 
      doSomething();
else
   doSomethingElse();

which is obviously wrong, since the else associates with the inner if . 這顯然是錯誤的，因爲else與內部同事if 。

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Edit: Since this is getting some attention, I'll clarify my view. 編輯：由於這引起了一些關注，我將澄清我的觀點。 The question I was answering is: 我回答的問題是：

What's the benefit of using the 1st version? 使用第一個版本有什麼好處？

Which I have described. 我已經描述過了。 There are some benefits. 有一些好處。 But, IMO, "always" rules don't always apply. 但是，IMO，“永遠”規則並不總是適用。 So I don't wholly support 所以我不完全支持

Always use a { } block - even for a single line // not OK, why ??? 總是使用{}塊 - 即使是單行//不行，爲什麼???

I'm not saying always use a {} block. 我並不是說總是使用{}塊。 If it's a simple enough condition & behavior, don't. 如果這是一個簡單的條件和行爲，不要。 If you suspect someone might come in later & change your code to add functionality, do. 如果您懷疑有人可能會稍後進入並更改您的代碼以添加功能，請執行此操作。

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#3樓

it is more intuitive and easily understandable. 它更直觀，更容易理解。 It makes the intent clear. 它使意圖清晰。

And it ensures that the code doesn't break when a new user might unknowingly miss the { , } while adding a new code statement. 並且它確保當新用戶在添加新代碼語句時可能在不知不覺中錯過{ ， }時代碼不會中斷。

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#4樓

It's very easy to accidentally change control-flow with comments if you do not use { and } . 如果不使用{和}則很容易通過註釋意外更改控制流。 For example: 例如：

if (condition)
  do_something();
else
  do_something_else();

must_always_do_this();

If you comment out do_something_else() with a single line comment, you'll end up with this: 如果你用單行評論註釋掉do_something_else() ，你最終會得到：

if (condition)
  do_something();
else
  //do_something_else();

must_always_do_this();

It compiles, but must_always_do_this() isn't always called. 它編譯，但must_always_do_this()並不總是被調用。

We had this issue in our code base, where someone had gone in to disable some functionality very quickly before release. 我們在代碼庫中遇到了這個問題，有人在發佈之前很快就禁用了某些功能。 Fortunately we caught it in code review. 幸運的是，我們在代碼審查中發現了它。

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#5樓

It makes your code more readable by clearly defining the scope of your loops and conditional blocks. 它通過清楚地定義循環和條件塊的範圍，使您的代碼更具可讀性。 It also saves you from accidental mistakes. 它還可以避免意外錯誤。

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#6樓

If you are a compiler, it doesn't make any difference. 如果您是編譯器，它沒有任何區別。 Both are the same. 兩者都是一樣的。

But for programmers, the first one is more clear, easy to read and less error-prone. 但對於程序員來說，第一個更清晰，易於閱讀且不易出錯。