布尔为int的转换 [英] bool to int conversion

问题描述

如何便携式是这种转换。我可以肯定地说这两个断言通过？

  INT X = 4℃; 5;
断言（X == 1）;X = 4大于5;
断言（X == 0）;
 

不要问为什么。我知道这是丑陋的。谢谢你。

解决方案

  INT X = 4℃; 5;
 

完全便携。标准的一致性。 布尔到 INT 的转换是隐含的！

§4.7/ 4来自C ++标准说（积分的转换的）

  

如果来源类型为布尔，值 假转换到零并
  值 真正转换一个

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至于C，据我知道有没有布尔在C.（1999年以前），所以，布尔到 INT 的转换是在C ++相关只。在C， 4℃; 5 计算结果为 INT 值，在此情况下，该值为 1 ， 4方式＆gt; 5 将评估为 0

编辑：延斯在注释中说，C99具有 _Bool 键入。 布尔是 stdbool.h 头文件中定义的宏。 真正和假在 stdbool.h 也定义的宏

§7.16从C99说：

  

宏 布尔 扩展到_Bool。

  
  

[..] 真正 它扩展成整型常量的 1 假
  它扩展成整型常量的 0 ，[..]

How portable is this conversion. Can I be sure that both assertions pass?

int x = 4<5;
assert(x==1);

x = 4>5;
assert(x==0);

Don't ask why. I know that it is ugly. Thank you.

解决方案

int x = 4<5;

Completely portable. Standard conformant. bool to int conversion is implicit!

§4.7/4 from the C++ Standard says (Integral Conversion)

If the source type is bool, the value false is converted to zero and the value true is converted to one.

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As for C, as far as I know there is no bool in C. (before 1999) So bool to int conversion is relevant in C++ only. In C, 4<5 evaluates to int value, in this case the value is 1, 4>5 would evaluate to 0.

EDIT: Jens in the comment said, C99 has _Bool type. bool is a macro defined in stdbool.h header file. true and false are also macro defined in stdbool.h.

§7.16 from C99 says,

The macro bool expands to _Bool.

[..] true which expands to the integer constant 1, false which expands to the integer constant 0,[..]

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