問(wèn)題描述

在最近的代碼審查中，一位貢獻(xiàn)者試圖強(qiáng)制以下列方式對(duì)指針執(zhí)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(diǎn)，因?yàn)樗鞔_表示確保此指針不為 NULL"，但我會(huì)反駁說(shuō)，任何正在處理此代碼的人都會(huì)理解使用指針if 語(yǔ)句中的變量隱式檢查 NULL.另外我覺(jué)得第二種方法引入同類錯(cuò)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(diào)試絕對(duì)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(jù)我的經(jīng)驗(yàn)，if (ptr) 或 if (!ptr) 形式的測(cè)試是首選.它們不依賴于符號(hào) NULL 的定義.他們不會(huì)暴露意外分配的機(jī)會(huì).它們清晰簡(jiǎn)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(píng)論中指出的那樣，它們與 C++ 類(例如 auto_ptr)兼容，這些類是充當(dāng)指針的對(duì)象并提供到 bool 來(lái)啟用這個(gè)習(xí)語(yǔ).對(duì)于這些對(duì)象，與 NULL 的顯式比較必須調(diào)用到指針的轉(zhuǎn)換，這可能具有其他語(yǔ)義副作用，或者比 bool 的簡(jiǎn)單存在檢查更昂貴轉(zhuǎn)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(shuō)明含義而沒(méi)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(jià)是冗余的特異性.下一個(gè)合乎邏輯的事情是編寫(xiě) if ((ptr != NULL) == TRUE) 并且這種方式是瘋狂的.C語(yǔ)言很清楚，一個(gè)由if、while等測(cè)試的布爾值具有特定含義，非零值為真，零為假.冗余并沒(méi)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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