setjmp与longjmp

#include <stdio.h>
#include <setjmp.h>

jmp_buf buf;

banana(){
    printf("in banana() \n");
    longjmp(buf,1); 

    printf("you'll never see this,because i longjmp'd");

}

main()
{
    if(setjmp(buf))
        printf("back in main\n");
    else{
        printf("first time through\n");
        banana();
    }

}

（代码段引自《C专家编程》：p）

这段代码的打印结果是：

first time through

in banana()

back in main