在c ++中，仅在全局范围内允许使用“表达式”来初始化全局对象。 在标准中哪里可以找到？

Question

The commented out expression below doesn't compile, because it is in the global scope. But where in the C++ Standard do I find something that relates to this restriction? As I recall, expressions are allowed in global scope only to initialize global objects. I have already looked into Chapter 5 Expressions , to no avail.

#include <iostream>
//std::cout.setf(std::ios_base::hex, std::ios_base::basefield);


int main()
{
    std::cout.setf(std::ios_base::hex, std::ios_base::basefield);
} 

Answer 1

I believe it is all going down to 3.5 Program and linkage :

1) A program consists of one or more translation units (Clause 2) linked together. A translation unit consists of a sequence of declarations.
translation-unit:
declaration-seq opt

Following that syntax description you'll find what is allowed in a declaration-seq and what is allowed in each declaration . And as can be seen a regular statement is not allowed at translation-unit level.