是C / C ++布尔类型始终保证typecast'ed为int时为0或1? [英] Is C/C++ bool type always guaranteed to be 0 or 1 when typecast'ed to int?
问题描述
许多编译器似乎只保留0或1的布尔值,但我不知道这将始终工作:
int类型的= 2;
布尔B = A;
INT C = 3 + B; // 4或5?
是:
在C ++(§4.5/ 4):
bool类型的右值可
转换成int类型的右值,
以虚假成为零和真
成为一体。
块引用>在C,当值转换为
_Bool
,就变成0或1(§6.3.1.2/ 1):
当任何标值被转换为
_Bool,结果是0,如果值进行比较等于0;否则,
结果是1。
块引用>当转换为
INT
,这是pretty直线前进。INT
可容纳0和1,所以有一个在价值没有改变(§6.3.1.3)。Many compilers seem to be keeping only 0 or 1 in bool values, but I'm not sure this will always work:
int a = 2; bool b = a; int c = 3 + b; // 4 or 5?
解决方案Yes:
In C++ (§4.5/4):
An rvalue of type bool can be converted to an rvalue of type int, with false becoming zero and true becoming one.
In C, when a value is converted to
_Bool
, it becomes 0 or 1 (§6.3.1.2/1):When any scalar value is converted to _Bool, the result is 0 if the value compares equal to 0; otherwise, the result is 1.
When converting to
int
, it's pretty straight-forward.int
can hold 0 and 1, so there's no change in value (§6.3.1.3).这篇关于是C / C ++布尔类型始终保证typecast'ed为int时为0或1?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!