C语言变长数组

C语言变长数组
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我们知道，传统的C语言是不能像C++那样支持变长数组的，也就是说数组的长度是在编译期就确定下来的，不能在运行期改变。C99标准定义的C语言新特性，新增的一项功能可以允许在C语言中使用变长数组。

C99 gives C programmers the ability to use variable length arrays, which are arrays whose sizes are not known until run time. A variable length array declaration is like a fixed array declaration except that the array size is specified by a non-constant expression. When the declaration is encountered, the size expression is evaluated and the array is created with the indicated length, which must be a positive integer. Once created, variable length array cannot change in length. Elements in the array can be accessed up to the allocated length; accessing elements beyond that length results in undefined behavior. There is no check required for such out-of-range accesses. The array is destroyed when the block containing the declaration completes. Each time the block is started, a new array is allocated.

以上就是C99标准对C语言变长数组的说明.

C语变长数组,测试所用的源代码很简单，如下所示：

1. //文件名：dynarray.c
2. //编译环境： bloodshed dev-c/c++ 4.9
3. #include <stdio.h>
4. #define bzero(b,len) (memset((b), '/0', (len)), (void) 0)
5. 
   
7. int main(int argc, char *argv[])
8. {
10.   int i, n;
11. 
    
12.   n = atoi(argv[1]);
13.   
14.   char arr[n+1];
16.   bzero(arr, (n+1) * sizeof(char));
17. 
    
19.   for (i = 0; i < n; i++) {
21.     arr[i] = (char)('A' + i);
23.   }
25.   arr[n] = '/0';
27.   printf("%s/n", arr);
28. 
    
30.   getchar();
31.   return (0);
32. 
    
34.  }

上述程序名为dynarray.c，其工作是把参数argv[1]的值n加上1作为变长数组arr的长度，变长数组arr的类型为char。然后向数组中写入一些字符，并将写入的字符串输出。

在支持c99标准的IDE上编译后， 在命令提示符下，运行： 

c:/c99_test/dynarray.exe 6

将输出: 

ABCDEF