c++ - 为什么int&a=10;在古代 C++ 编译器中有效吗？

Question

我只是想知道为什么像 Turbo c++ 3.0(蓝屏 IDE)和 Borland Turbo C++ 4.5 等古老的编译器在下面的程序中没有报告任何错误。

#include <iostream.h>
int main()
{
  int& a=10;
  cout<<a;
  return 0;
}

上述程序不会被现代 C++ 编译器接受，但为什么古代编译器允许这样做呢？他们只是在上面的程序中显示单个警告。

Answer 1

它曾经是有效的 C++ 将引用绑定(bind)到临时对象，因此您可以通过例如double 到需要 int& 的函数，如 The Design & Evolution of C++ 中所述§3.7:

I made one serious mistake, though, by allowing a non-const reference to be initialized by a non-lvalue. [...]
The reason to allow references to be initialized by non-lvalues was to allow the distinction between call-by-value and call-by-reference to be a detail specified by the called function and of no interest to the caller. For const references, this is possible, for non-const references it is not. For Release 2.0 the definition of C++ was changed to reflect this.

在 C++ 2.0(和 ISO C++)中，临时对象只能绑定(bind)到 const 引用。