为NULL总是假的？ [英] Is NULL always false?

问题描述

它是安全的假设， NULL 总是转换为false用C？

Is it safe to assume that NULL always translates to false in C?

void *somePtr = NULL;

if (!somePtr) {
  /* This will always be executed? */
}

还是应该对价值的明确检查 NULL 进行？

推荐答案

是的。 NULL计算结果为false，由于C认为任何非零值true任何零值false。 NULL本质上是零地址，并在比较中也可以这样处理，我相信会被提升到了布尔检查一个int。我希望，你的code是可读的任何人熟悉C，虽然我可能会做出明确的检查

Yes. NULL evaluates to false, since C considers any non-zero value true and any zero value false. NULL is essentially the zero address and is treated as such in comparisons, and I believe would be promoted to an int for the boolean check. I would expect that your code is readable to anyone familiar with C although I would probably make the check explicit.

在C和C ++编程，两个空
  指针保证比较
  等于; ANSI C保证任何空
  指针将等于0的
  一个整型比较;
  此外，宏NULL被定义
  作为一个空指针常数，即
  0值（无论是作为一个整数类型或
  转换为一个指向void），因此
  空指针将相当于
  NULL。

In C and C++ programming, two null pointers are guaranteed to compare equal; ANSI C guarantees that any null pointer will be equal to 0 in a comparison with an integer type; furthermore the macro NULL is defined as a null pointer constant, that is value 0 (either as an integer type or converted to a pointer to void), so a null pointer will compare equal to NULL.

参考：<一href=\"http://en.wikipedia.org/wiki/Null_pointer#Null_pointer\">http://en.wikipedia.org/wiki/Null_pointer#Null_pointer

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