C语言 字符数组后的奇怪字符
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Strange character after an array of characters
提问by user2166357
I am a real beginner to C, but I am learning!
我是 C 的真正初学者，但我正在学习！
I've stumbled upon this problem before and decided to ask what the reason for it is. And please explain your answers so I can learn.
我之前偶然发现了这个问题，并决定询问它的原因是什么。请解释您的答案，以便我学习。
I have made a program which allows you to input 5 characters and then show the characters you wrote and also revert them, example: "asdfg" - "gfdsa". The weird thing is that a weird character is shown after the original characters that was inputted.
我制作了一个程序，它允许您输入 5 个字符，然后显示您编写的字符并还原它们，例如：“asdfg”-“gfdsa”。奇怪的是，在输入的原始字符之后显示了一个奇怪的字符。
Here is the code:
这是代码：
char str[5];
char outcome[] = "OOOOO";
int i;
int u;
printf("Enter five characters\n");
scanf("%s", str);
for(i = 4, u = 0; i >=0; u++, i--){
outcome[i] = str[u];
}
printf("\nYou wrote: %s. The outcome is: %s.", str , outcome);
return 0;
If I enter: "asdfg" it shows: "asdfg?", why is that?
如果我输入：“asdfg”，它会显示：“asdfg？”，这是为什么？
Thank you for your time and please explain your answers :)
感谢您的时间，请解释您的答案:)
回答by Mike
Because there's no null terminator. In C a "string" is a sequence of continuous bytes (chars) that end with a sentinel character called a null terminator ('\0'). Your code takes the input from the user and fills all 5 characters, so there's no "end" to your string. Then when you print the string it will print your 5 characters ("asdfg") and it will continue to print whatever garbage is on the stack until it hits a null terminator.
因为没有空终止符。在 C 中，“字符串”是一系列连续字节（字符），以称为空终止符 ( '\0')的标记字符结尾。您的代码接受用户的输入并填充所有 5 个字符，因此您的字符串没有“结尾”。然后，当您打印字符串时，它将打印您的 5 个字符 ( "asdfg")，并且它将继续打印堆栈上的任何垃圾，直到遇到空终止符。
char str[6] = {'str[6];
'}; //5 + 1 for 'str[5] = '##代码##'
', initialize it to an empty string
...
printf("Enter five characters\n");
scanf("%5s", str); // limit the input to 5 characters
The nice thing about the limit format specificer is that even if the input is longer than 5 characters, only 5 will be stored into your string, always leaving room for that null terminator.
限制格式指定器的好处是，即使输入长度超过 5 个字符，也只有 5 个字符会存储到您的字符串中，始终为空终止符留出空间。
回答by user2166357
Your string str[5];is too short.
你的字符串str[5];太短了。
It should be
它应该是
##代码##And when you print it the code goes out of bound of that array.
当你打印它时，代码超出了该数组的范围。
You also have to set a null terminating character to str[] array to mark the end of the array.
您还必须为 str[] 数组设置一个空终止字符以标记数组的结尾。
##代码##