我可以使用 if (pointer) 而不是 if (pointer != NULL) 吗?

2021-12-12 00:00:00 pointers null if-statement c++ null-pointer

通过简单地编写 if(pointer) 来检查指针是否为 NULL 是否安全，或者我是否必须使用 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)?

推荐答案

你可以；空指针被隐式转换为布尔值 false 而非空指针被转换为 true.来自 C++11 标准，关于布尔转换的部分:

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:

算术、无作用域枚举、指针或指向成员类型的指针的纯右值可以转换为类型的纯右值布尔.零值、空指针值或空成员指针值被转换为假;任何其他值都转换为真.类型的纯右值std::nullptr_t可以转换为纯右值类型bool;结果值是假.

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 to false; any other value is converted to true . A prvalue of type std::nullptr_t can be converted to a prvalue of type bool ; the resulting value is false .

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