問題描述

在最近的代碼審查中，一位貢獻者試圖強制以下列方式對指針執行所有 NULL 檢查:

In a recent code review, a contributor is trying to enforce that all NULL checks on pointers be performed in the following manner:

int * some_ptr;
// ...
if (some_ptr == NULL)
{
    // Handle null-pointer error
}
else
{
    // Proceed
}

代替

int * some_ptr;
// ...
if (some_ptr)
{
    // Proceed
}
else
{
    // Handle null-pointer error
}

我同意他的方式更清楚一點，因為它明確表示確保此指針不為 NULL"，但我會反駁說，任何正在處理此代碼的人都會理解使用指針if 語句中的變量隱式檢查 NULL.另外我覺得第二種方法引入同類錯誤的可能性較小:

I agree that his way is a little more clear in the sense that it's explicitly saying "Make sure this pointer is not NULL", but I would counter that by saying that anyone who's working on this code would understand that using a pointer variable in an if statement is implicitly checking for NULL. Also I feel the second method has a smaller chance of introducing a bug of the ilk:

if (some_ptr = NULL)

查找和調試絕對是一件痛苦的事情.

which is just an absolute pain to find and debug.

您更喜歡哪種方式，為什么?

Which way do you prefer and why?

推薦答案

根據我的經驗，if (ptr) 或 if (!ptr) 形式的測試是首選.它們不依賴于符號 NULL 的定義.他們不會暴露意外分配的機會.它們清晰簡潔.

In my experience, tests of the form if (ptr) or if (!ptr) are preferred. They do not depend on the definition of the symbol NULL. They do not expose the opportunity for the accidental assignment. And they are clear and succinct.

正如 SoapBox 在評論中指出的那樣，它們與 C++ 類(例如 auto_ptr)兼容，這些類是充當指針的對象并提供到 bool 來啟用這個習語.對于這些對象，與 NULL 的顯式比較必須調用到指針的轉換，這可能具有其他語義副作用，或者比 bool 的簡單存在檢查更昂貴轉換意味著.

As SoapBox points out in a comment, they are compatible with C++ classes such as auto_ptr that are objects that act as pointers and which provide a conversion to bool to enable exactly this idiom. For these objects, an explicit comparison to NULL would have to invoke a conversion to pointer which may have other semantic side effects or be more expensive than the simple existence check that the bool conversion implies.

我更喜歡能說明含義而沒有不需要的文本的代碼.if (ptr != NULL) 與 if (ptr) 具有相同的含義，但代價是冗余的特異性.下一個合乎邏輯的事情是編寫 if ((ptr != NULL) == TRUE) 并且這種方式是瘋狂的.C語言很清楚，一個由if、while等測試的布爾值具有特定含義，非零值為真，零為假.冗余并沒有讓它更清楚.

I have a preference for code that says what it means without unneeded text. if (ptr != NULL) has the same meaning as if (ptr) but at the cost of redundant specificity. The next logical thing is to write if ((ptr != NULL) == TRUE) and that way lies madness. The C language is clear that a boolean tested by if, while or the like has a specific meaning of non-zero value is true and zero is false. Redundancy does not make it clearer.

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