用C空字节和数组 [英] Null byte and arrays in C

问题描述

如果我宣布的字符数组说10个字符，像这样......

If I declare a char array of say 10 chars like so...

char letters[10];

我在创建一组的内存位置重新psented从那么指数0-9个字符$ P $ 10日指数是空字节？

am I creating a set of memory locations that are represented as chars from index 0-9 then the 10th index is the null byte?

如果这是否意味着我真的在内存中创建11个地点为数组（0至10）的最后一个元素是空字节还是我在存储器（0〜9）10个地点则C加在新的位置空字节（所以数组是1个字节的时间比我申报）？

if so does that mean I'm really creating 11 locations in memory for the array (0 to 10) with the last element being the null byte or do I have 10 locations in memory (0 to 9) then C adds the null byte at a new position (so the array is 1 byte longer than I declared)?

感谢

推荐答案

好像你用数组和字符串混淆。结果
当你声明

Seems like you are confused with arrays and strings.
When you declare

char letters[10] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'};  

然后它保留仅仅10中的存储器位置连续字节。

then it reserves only 10 contiguous bytes in a memory location.

  2000  2001  2002  2003  2004  2005  2006  2007  2008  2009  //memory addresses. I assumed it is to be starting from 200 for simplification. 
 +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+
 |     |     |     |     |     |     |     |     |     |     |
 | '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9' |
 |     |     |     |     |     |     |     |     |     |     |
 +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+

在C索引从 0 启动。您可以从字母访问分配的内存位置[0] 到信[9] 。访问位置信[10] 将调用的未定义行为即可。但是，当你声明这样

In C indexing starts from 0. You can access your allocated memory location from letters[0] to letters[9]. Accessing the location letters[10] will invoke undefined behavior. But when you declare like this

char *letters = "0123456789";  

或

char letters[11] = 0123456789";    

再有空间的11字节的内存分配; 10 0123456789 和一个 \\ 0 （NUL字符）。

then there are 11 bytes of space are allocated in memory; 10 for 0123456789 and one for \0 (NUL character).

 2000  2001  2002  2003  2004  2005  2006  2007  2008  2009  2010 //memory addresses. I assumed it is to be starting from 200 for simplification. 
+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-------+
|     |     |     |     |     |     |     |     |     |     |       |
| '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9' | '\0'  |
|     |     |     |     |     |     |     |     |     |     |       |
+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-------+  
                                                                ^
                                                                | NUL character   

再举一个例子

#include <stdio.h>

int main(){
   char arr[11];
   scanf("%s", arr);
   printf("%s", arr);

   return 0;
} 

输入：

asdf  

输出：

asdf

现在对内存位置看看

 +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-------+
 |     |     |     |     |     |     |     |     |     |     |       |
 | 'a' | 's' | 'd' | 'f' |'\0' |     |     |     |     |     |       |
 |     |     |     |     |     |     |     |     |     |     |       |
 +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-------+  

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