GNU C Variable-Size Arrays (The GNU C Library)

#### 3.2.7.4 GNU C Variable-Size Arrays ¶

In GNU C, you can replace most uses of `alloca` with an array of variable size. Here is how `open2` would look then:

    int open2 (char *str1, char *str2, int flags, int mode)
    {
      char name[strlen (str1) + strlen (str2) + 1];
      stpcpy (stpcpy (name, str1), str2);
      return open (name, flags, mode);
    }

But `alloca` is not always equivalent to a variable-sized array, for several reasons:

- A variable size array’s space is freed at the end of the scope of the name of the array. The space allocated with `alloca` remains until the end of the function.
- It is possible to use `alloca` within a loop, allocating an additional block on each iteration. This is impossible with variable-sized arrays.

NB: If you mix use of `alloca` and variable-sized arrays within one function, exiting a scope in which a variable-sized array was declared frees all blocks allocated with `alloca` during the execution of that scope.