C语言之setjmp

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

static jmp_buf buf;

int main(void)
{
   volatile int b = 3;

   if (setjmp(buf) != 0)
   {
      printf("%d\n", b);
      exit(0);
   }
   b = 5;
   longjmp(buf, 1);
   
   return 0;
}

Answer: 5

The setjmp function stores context information for a “non-local goto”, and returns 0. Thelongjmp function transfers control to the setjmp call that initializedbuf, and execution continues from this point as if setjmp had returned 1.

Note: a non-volatile automatic variable that has been modified after setjmp becomes indeterminate afterlongjmp. Without the volatile qualifier, this program’s behavior would be undefined. This rule permits better optimization of code.

关键点在于理解setjmp以及longjmp，（http://en.wikipedia.org/wiki/Setjmp.h ）第一次运行到setjmp，会设置jmp_buf，然后返回0。当调用longjmp时，会把longjmp里面的非0值作为setjmp的返回值返回（如果longjmp的value参数为0，setjmp恢复后返回1，也就是当恢复到setjmp存储点的时候，setjmp一定不会返回0）。——Veda原型