c++ - 现在允许为 std::string 分配一个数字吗？

Question

考虑以下代码片段:

#include <iostream>
int main() {
    std::string foo;
    foo = -1; // why is the compiler not complaining about this?
    std::cout << "1" << std::endl;
    std::cout << foo << std::endl;
    std::cout << "2" << std::endl;
}

实际输出(ideone.com C++14模式和GCC 4.8.4):

<no output>

问题:

1. 为什么代码片段会编译？
2. 注释掉 foo = -1，我得到了正确的标准输出(1 和 2)。编译器使用 foo = -1; 编译导致后续 cout 失败的原因是什么？

Answer 1

foo = -1;

解析为 std::string::operator=(char)自从 -1是 int和 int理论上可以转换为 char .

我不清楚标准在 int 时的含义。不代表有效的 char .看起来在您的实现中，程序崩溃了。

更新

来自 C++11 标准(重点是我的):

3.9.1 Fundamental types

1 Objects declared as characters (char) shall be large enough to store any member of the implementation’s basic character set. If a character from this set is stored in a character object, the integral value of that character object is equal to the value of the single character literal form of that character. It is implementation-defined whether a char object can hold negative values.

看来您必须查阅编译器的文档才能了解它是否允许 char对象来保存负值，如果是，它如何处理这些对象。