不确定成员个数的数组的问题

carol_sun

一直说，当数组元素个数不确定的时候，我们可以用动态数组
说数组不支持运行时才确定个数的情况
但是我用下面的程序，编译器也不报错，也能正常运行，这是为什么呢

   int pp;
    scanf("%d", &pp);

    int dd[pp];
    dd[0] = 10;
    dd[1] = 11;

和编译器有关系？ 我用的是gcc 2.95

churchmice

还真能过

[ 本帖最后由 churchmice 于 2009-9-21 12:56 编辑 ]

churchmice

查了一下，属于gcc的extension,也是c99标准的一部分

Variable-length automatic arrays are allowed in ISO C99, and as an
extension GCC accepts them in C89 mode and in C++.  (However, GCC's
implementation of variable-length arrays does not yet conform in detail
to the ISO C99 standard.)  These arrays are declared like any other
automatic arrays, but with a length that is not a constant expression.
The storage is allocated at the point of declaration and deallocated
when the brace-level is exited.  For example:

     FILE *
     concat_fopen (char *s1, char *s2, char *mode)
     {
       char str[strlen (s1) + strlen (s2) + 1];
       strcpy (str, s1);
       strcat (str, s2);
       return fopen (str, mode);
     }

Jumping or breaking out of the scope of the array name deallocates the
storage.  Jumping into the scope is not allowed; you get an error
message for it.

info gcc -> C Extension -> Arrays of Variable Length
自己慢慢看吧

zyl19861126

C99的新特性， 动态数组

lenky0401

呵呵 之前正好看了Gnu's C扩展，从浏览器的历史记录里找出来了

http://www.ddj.com/cpp/184401956

carol_sun

谢谢churchmice
那局部变量的动态数组，我们不是就可以不用自己去new了

maxxfire

栈上动态分配，应该相当于alloca

anthony1983

不是所有的编译器都支持，能不这样写，就不要这样写吧