大小端与栈生长方向

为这个疑问着迷。想弄清楚，参考了http://blog.sina.com.cn/s/blog_a0e859400101279a.html。

/*
 * find_stack_direction.c
 * To find the growing direction of stack and 
 * to recognize the pattern of data storage of the computer.
 */
#include <stdio.h>

static int stack_dir;

void find_stack_direction (void);

int main (void){
  if (1 == stack_dir){
    puts ("stack grew upward.");
  }
  else{
    puts ("stack grew downward.");
  }

  //little-endian or big-endian?
  {
    int a = 1;
    if (*(char *)&a == 1){
      puts ("Little-Eidian.");
    }
    else{
      puts ("Big-Endian.");
    }
  }
  return 0;
}

void find_stack_direction (void){
  static char * addr = NULL;
  char dummy;
  if (NULL == addr){
    addr = &dummy;
    find_stack_direction ();
  }
  else{
    if (addr > &dummy){ // upwards
      stack_dir = 1;
    }
    else{ // downwards
      stack_dir = -1;
    }
  }
}

结果：

stack grew download.
Little-Eidian.

仔细想想，其实不需要递归了。很随意的也可以，只要比较caller和callee的非静态局部变量地址大小就ok了。

#include <stdio.h>

char * p = (char *)0x7FFFFFFF;
void f ();

void main (){
    char b;
    p = &b;
    f ();
}

void f (){
    char a;
    if ( &a > p)
        puts ("stack grew upward.");
    else
        puts ("stack grew downward.");
}

结果：

stack grew downward.

更简练的代码可以这样（不过不推荐这样写，因为返回了局部变量的地址不安全，不过对于这个测试来说无妨）。

#include <stdio.h>

char * b (char c){
    return &c;
}

void main (){
    char a;
    if (&a < b (a))
        puts ("stack grew upward.");
    else
        puts ("stack grew downward.");
}