为什么字符串文字比较是 C++ 中实现定义的行为？

Question

我在 The C++ Programming Language special 3rd edition 中阅读了以下内容：

是否将两个相同的字符文字分配为一个由实现定义（§C.1）。

const char* p="Heraclitus";
const char* q="Heraclitus";

void g ()
{
       if (p == q ) cout << "one!\n"; // result is implementation defined
       // ...
}

请注意，== 在应用于指针时比较地址（指针值），而不是指向的值。

我已经尝试在 gcc 4.8.1 和 MSVS 2010 上执行以下程序

#include <iostream>
int main()
{
    const char* p="Heraclitus";
    const char* q="Heraclitus";
    if(p==q)
        std::cout<<"fine!!!";
    else
        std::cout<<"!fine";
}

输出：

很好！！！（在 gcc 4.8.1 上）

!很好（在 MSVS 2010 上）

为什么将其保留为实现定义的行为？这是什么原因？

Answer 1

我们可以在这个 comp.std.c thread: History question: String literals 中找到一个基本原理，它说：

GCC might have served as an example but not as motivation. Partly the desire to have string literals in ROMmable data was to support, er, ROMming. I vaguely recall having used a couple of C implementations (before the X3J11 decision was made) where string literals were either automatically pooled or stored in a constant data program section. Given the existing variety of practice and the availability of an easy work-around when the original UNIX properties were wanted, it seemed best to not try to guarantee uniqueness and writability of string literals.

为什么字符串文字比较是 C++ 中实现定义的行为？

Why string literal comparison is implementation defined behavior in C++?

c++

g++

visual-studio-2010

string-literals

g++4.8