問題描述
通過簡單地編寫 if(pointer) 來檢查指針是否為 NULL 是否安全，或者我是否必須使用 if(pointer != NULL)?
Is it safe to check a pointer to not being NULL by writing simply if(pointer) or do I have to use if(pointer != NULL)?
推薦答案
你可以；空指針被隱式轉換為布爾值 false 而非空指針被轉換為 true.來自 C++11 標準，關于布爾轉換的部分:
You can; the null pointer is implicitly converted into boolean false while non-null pointers are converted into true. From the C++11 standard, section on Boolean Conversions:
算術、無作用域枚舉、指針或指向成員類型的指針的純右值可以轉換為類型的純右值布爾.零值、空指針值或空成員指針值被轉換為假;任何其他值都轉換為真.類型的純右值std::nullptr_t可以轉換為純右值類型bool;結果值是假.
A prvalue of arithmetic, unscoped enumeration, pointer, or pointer to member type can be converted to a prvalue of type
bool. A zero value, null pointer value, or null member pointer value is converted tofalse; any other value is converted totrue. A prvalue of typestd::nullptr_tcan be converted to a prvalue of typebool; the resulting value isfalse.
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