C语言的异常机制--setjump()和longjump()实现

/* -------------------------------------------------------------------------
** File : cexcept.c                                                        *
** Coder: Spark Song.                                                      * 
** Note : Use the example code from 《C Interfaces and Implementations》   *  
** -------------------------------------------------------------------------
*/
#include <setjmp.h>
#include <stdlib.h>
#include <stdio.h>
#include <assert.h>
int Allocation_handled = 0;
jmp_buf Allocate_Failed;
void *allocate(unsigned n)
{
    void * new = (void *)malloc(n);
    if (new)
        return new;
    if (Allocation_handled)          /* 如果实例化了异常处理程序的话... */
        longjmp(Allocate_Failed, 1); /* 产生异常，并抛出 */
    
    assert(0); /* 如果没有实例化异常处理程序，则此断言会报出运行期的错误 */
}
int main(int argc, char *argv[])
{
    char *buf = 0;
    int count = 0;
    Allocation_handled = 1;         /* 设置实例化异常的标志，设为1表示实例化了异常处理程序 */ 
    if (setjmp(Allocate_Failed))    /* 实例化异常 */
    {
        fprintf(stderr, "EXCEPT: Couldn't allocate the buffer/n"); 
        exit(EXIT_FAILURE);
    }      
        
    while(1)    /* 测试代码：一直分配内存，直到没有内存为止。没有内存时会触发异常 */
    {
        buf = (char *)allocate(4096000);         
        printf("Allocate successs, the count is: %d/n", count++);
    }
    Allocation_handled = 0;  
	return 0;