做负数在C / C返回false ++？ [英] Do negative numbers return false in C/C++?

问题描述

在评估整数在C / C ++布尔都是负数真的还是假的？难道他们总是真/假，无论编译器？

解决方案

所有非零值将被转换为真正和零值假。随着负数为非零，它们都转换为真正。

从C ++ 11标准（重点煤矿）报价：

  

4.12布尔转换[conv.bool]

  
  

1的算术，无范围枚举，指针，或指针的prvalue
  为成员类型可以转换为bool类型的prvalue。 零
  值，空指针值或空成员指针值转换
  到假;任何其他的值转换为真正。 A型prvalue
  的std :: nullptr_t可转换为bool类型的prvalue;该
  得到的值是假的。

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他们是永远真/假，无论编译器？

您将只能得到上述担保时，你的编译器是符合标准的，或者至少与标准的特定部分的规定。在实践中，所有的编译器有这个标准的行为，所以没有太多的担心。

When evaluating integers as booleans in C/C++, are negative numbers true or false? Are they always true/false regardless of compilers?

解决方案

All non-zero values will be converted to true, and zero values to false. With negative numbers being non-zero, they are converted to true.

Quoting from the C++11 standard (emphasis mine):

4.12 Boolean conversions [conv.bool]

1 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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Are they always true/false regardless of compilers?

You will only get the above guarantee when your compiler is standards-compliant, or at least, complies with this specific part of the standard. In practice, all compilers have this standard behavior, so there isn't much to worry about.

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