c++ - 为什么 cin 中断时会发生变量？ C++

Question

我有以下代码片段:

    int a = 1;
    double b = 3.14;
    string c = "hi";

    cin >> a >> b >> c;
    cout << a << " " << b << " " << c << endl;

如果我输入 apple 11 tammy，为什么它会显示:0 3.14 hi 而不是:1 3.14 hi？

为什么cin被破坏时a的值会改变？

Answer 1

Why does the value of a change when cin is broken?

这是 std::basic_istream::operator>> 的预期行为自 C++11 起；如果提取失败，该值将设置为 0 .

If extraction fails, zero is written to value and failbit is set. If extraction results in the value too large or too small to fit in value, std::numeric_limits<T>::max() or std::numeric_limits<T>::min() is written and failbit flag is set.

注意在failbit之后被设置后，将不会执行以下输入；这意味着 b和 c将保持其原始值。

顺便说一句:在 C++11 之前，当提取失败时，该值将保持不变。

If extraction fails (e.g. if a letter was entered where a digit is expected), value is left unmodified and failbit is set.