Question

向Stack Overflow社区致意。我正在尝试从基础知识中学习C ++，并遇到一些奇怪的（至少对我来说）行为。这是我的“你好世界”

#include <iostream>

int main() 
{
    std::cout << "Enter Thing! " << std::endl;
    char Thing[]="";
    std::cin >> Thing;
    std::cout << "Thing is " << Thing << "!" << std::endl;
    int i=0;
    while (i <= 10)
    {
        ++i;
         std::cout << "Thing is " << Thing << " in " << i << " while!" << std::endl; 
         std::cout << "i is " << i << "!" << std::endl;
    }
    std::cout << "Thing is " << Thing << " after while!" << std::endl;
    std::cout << "i is " << i << ".5!" << std::endl;
}

实际上让我烦恼的是它给出的输出。

Enter Thing!
thing
Thing is thing!
Thing is t☺ in 1 while!
i is 1!
Thing is t☻ in 2 while!
i is 2!
Thing is t♥ in 3 while!
i is 3!
Thing is t♦ in 4 while!
i is 4!
Thing is t♣ in 5 while!
i is 5!
Thing is t♠ in 6 while!
i is 6!
Thing is t in 7 while!
i is 7!
Thing is  in 8 while!
i is 8!
Thing is t       in 9 while!
i is 9!
Thing is t
 in 10 while!
i is 10!
Thing is t♂ in 11 while!
i is 11!
Thing is t♂ after while!
i is 11.5!

我真的不知道那里发生了什么。更重要的是，如果我添加“for”构造，例如

for (int i=4; i <=7; ++i)
    {
        std::cout << "i is " << i << "!" << std::endl;
        std::cout << "Thing is " << Thing << " for!" << std::endl;
    }
    std::cout << "i is " << i+3 << ".5!" << std::endl;    
    std::cout << "Thing is " << Thing << " after for!" << std::endl;

输出更改为更奇怪的事情

Enter Thing!
thing
Thing is thing!
Thing is thing☺ in 1 while!
i is 1!
Thing is thing☻ in 2 while!
i is 2!
Thing is thing♥ in 3 while!
i is 3!
Thing is thing♦ in 4 while!
i is 4!
Thing is thing♣ in 5 while!
i is 5!
Thing is thing♠ in 6 while!
i is 6!
Thing is thing in 7 while!
i is 7!
Thing is thin in 8 while!
i is 8!
Thing is thing   in 9 while!
i is 9!
Thing is thing
 in 10 while!
i is 10!
Thing is thing♂ in 11 while!
i is 11!
Thing is thing♂ after while!
i is 11.5!
i is 4!
Thing is t♦ for!
i is 5!
Thing is t♣ for!
i is 6!
Thing is t♠ for!
i is 7!
Thing is t for!
i is 14.5!
Thing is  after for!

可能是我是愚蠢的东西，但如果我甚至不能让最基本的东西发挥作用，我就无法继续学习。对不起，如果在某个时候已经回答了同样的问题，请尽力搜索但没有成功。所以你很乐意指出我在哪里愚蠢吗？感谢。

P.S。我使用NetBeans 8和Cygwin一起使用Win7x64m。

Answer 1

变量Thing是仅包含单个字符的数组。向其中写入多个字符将写出界限并导致未定义的行为。

空字符串文字""是单个字符的数组，即字符串终止符，编译器将使用它来初始化数组Thing为精确副本。

你基本上有两个解决方案，要么声明数组有更大的尺寸：

char Thing[128] = "";

或者您使用the standard C++ string class：

std::string Thing;

我绝对推荐后一种解决方案。

Answer 2

这是有问题的：

 char Thing[]="";

您正在创建一个单个字符的空数组，并将用户输入写入其中。

你第一次偶然得到了正确的输出，但随后数据被覆盖了，你得到了这个奇怪的输出。

创建具有足够缓冲区长度的字符串

char thing[256];

或使用字符串对象。

Answer 3

正如其他人的答案建议的那样，你使用你的char数组而不是真正初始化它（提供固定大小）。此外，这是C风格的编程。我强烈建议使用C ++ std::string而不是char - 数组，因为这不容易出错。

Answer 4

自编译代码以来，应修复本地声明的此类数组的大小。

char Thing[] = "";

这让你觉得'Thing'的大小是可变的错觉。简而言之，“Thing”的大小将根据右侧给出的初始值自动推断，这会使您输入的字符串写入内存中的意外位置，从而导致未定义的行为。

我无法理解C ++中的char []行为

4 个答案: