控制台打印时间功能产生1 [英] Printing time function to console produces 1

问题描述

几个开发人员，我想知道为什么:

A couple of developers and I were wondering why:

std::cout<<std::time<<std::endl;

打印出一个值1.该值代表什么，以及为什么值是1.

prints out a value of 1. What does the value represents, and why the value is of 1.

答案: 如何使用cout打印函数指针?

C ++标准指定:

4.12布尔转换

4.12 Boolean conversions

1算术，枚举，指针或成员指针的右值 可以将类型转换为bool类型的右值.

1 An rvalue of arithmetic, enumeration, pointer, or pointer to member type can be converted to an rvalue of type bool.

匿名引用:

这是为函数指针指定的唯一转换.

This is the only conversion specified for function pointers.

以下答案很好地介绍了为什么打印1而不是仅打印任何bool的解决方案，并解释了何时不会出现1.

The answer below nicely presents the solution as to why 1 was printed rather than just any bool and explained when 1 would not occur.

推荐答案

cppreference 表示:

指向非静态成员的指针没有指向的重载. volatile或函数指针(带签名的指针除外) (10-12)重载所接受).尝试输出此类对象 调用隐式转换为bool，并且对于任何非null指针 值，则打印值1(除非设置了boolalpha，在这种情况下 true会打印出来.)

There are no overload for pointers to non-static member, pointers to volatile, or function pointers (other than the ones with signatures accepted by the (10-12) overloads). Attempting to output such objects invokes implicit conversion to bool, and, for any non-null pointer value, the value 1 is printed (unless boolalpha was set, in which case true is printed).

因此，您将函数指针std::time转换为bool，并且始终是true，而没有boolalpha将输出设置为1.

So you get function pointer std::time converted to bool and it is always true that is without boolalpha set output as 1.

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