整型上溢除以-1异常问题

[无涯回头]

代码段（一）：
int a = 2147483648;
int b = a / -1;
printf(“%d,%d\n”,a, b);
代码段（二）：
int a = 2147483648;
int b = -1;
int c = a / b;
printf("%d,%d\n", a, c);
如上，代码一可正常输出，代码二提示浮点异常，烦请大神讲解下

[赵4老师]

理解和讨论之前请先学会如何观察！ 计算机组成原理→DOS命令→汇编语言→C语言（不包括C++）、代码书写规范→数据结构、编译原理、操作系统→计算机网络、数据库原理、正则表达式→其它语言（包括C++）、架构…… 对学习编程者的忠告： 多用小脑和手，少用大脑、眼睛和嘴，会更快地学会编程！ 眼过千遍不如手过一遍！ 书看千行不如手敲一行！ 手敲千行不如单步一行！ 单步源代码千行不如单步Debug版对应汇编一行！ 单步Debug版对应汇编千行不如单步Release版对应汇编一行！ 不会单步Release版对应汇编？在你想单步Release版C/C++代码片断的前面临时加一句DebugBreak();重建所有，然后在IDE中运行。（一般人我不告诉他！） VC调试时按Alt+8、Alt+7、Alt+6和Alt+5,打开汇编窗口、堆栈窗口、内存窗口和寄存器窗口看每句C对应的汇编、单步执行并观察相应堆栈、内存和寄存器变化，这样过一遍不就啥都明白了吗。 对VC来说，所谓‘调试时’就是编译连接通过以后，按F10或F11键单步执行一步以后的时候，或者在某行按F9设了断点后按F5执行停在该断点处的时候。 仅供参考：

/* FPRESET.C: This program uses signal to set up a
 * routine for handling floating-point errors.
 */

#include <stdio.h>
#include <signal.h>
#include <setjmp.h>
#include <stdlib.h>
#include <float.h>
#include <math.h>
#include <string.h>

jmp_buf mark;              /* Address for long jump to jump to */
int     fperr;             /* Global error number */

void __cdecl fphandler( int sig, int num );   /* Prototypes */
void fpcheck( void );

void main( void )
{
   double n1, n2, r;
   int jmpret;
   /* Unmask all floating-point exceptions. */
    _control87( 0, _MCW_EM );
   /* Set up floating-point error handler. The compiler
    * will generate a warning because it expects
    * signal-handling functions to take only one argument.
    */
    if( signal( SIGFPE, fphandler ) == SIG_ERR )

   {
      fprintf( stderr, "Couldn't set SIGFPE\n" );
      abort();   }

   /* Save stack environment for return in case of error. First 
    * time through, jmpret is 0, so true conditional is executed. 
    * If an error occurs, jmpret will be set to -1 and false 
    * conditional will be executed.
    */
   jmpret = setjmp( mark );
   if( jmpret == 0 )
   {
      printf( "Test for invalid operation - " );
      printf( "enter two numbers: " );
      scanf( "%lf %lf", &n1, &n2 );
      r = n1 / n2;
      /* This won't be reached if error occurs. */
      printf( "\n\n%4.3g / %4.3g = %4.3g\n", n1, n2, r );

      r = n1 * n2;
      /* This won't be reached if error occurs. */
      printf( "\n\n%4.3g * %4.3g = %4.3g\n", n1, n2, r );
   }
   else
      fpcheck();
}
/* fphandler handles SIGFPE (floating-point error) interrupt. Note
 * that this prototype accepts two arguments and that the 
 * prototype for signal in the run-time library expects a signal 
 * handler to have only one argument.
 *
 * The second argument in this signal handler allows processing of
 * _FPE_INVALID, _FPE_OVERFLOW, _FPE_UNDERFLOW, and 
 * _FPE_ZERODIVIDE, all of which are Microsoft-specific symbols 
 * that augment the information provided by SIGFPE. The compiler 
 * will generate a warning, which is harmless and expected.

 */
void fphandler( int sig, int num )
{
   /* Set global for outside check since we don't want
    * to do I/O in the handler.
    */
   fperr = num;
   /* Initialize floating-point package. */
   _fpreset();
   /* Restore calling environment and jump back to setjmp. Return 
    * -1 so that setjmp will return false for conditional test.
    */
   longjmp( mark, -1 );
}
void fpcheck( void )
{
   char fpstr[30];
   switch( fperr )
   {
   case _FPE_INVALID:
       strcpy( fpstr, "Invalid number" );
       break;
   case _FPE_OVERFLOW:
       strcpy( fpstr, "Overflow" );

       break;
   case _FPE_UNDERFLOW:
       strcpy( fpstr, "Underflow" );
       break;
   case _FPE_ZERODIVIDE:
       strcpy( fpstr, "Divide by zero" );
       break;
   default:
       strcpy( fpstr, "Other floating point error" );
       break;
   }
   printf( "Error %d: %s\n", fperr, fpstr );
}


Output

Test for invalid operation - enter two numbers: 5 0
Error 131: Divide by zero

[ztenv]

第一个，压根没有执行除法指令，而是执行了neg的指令 第二个，执行了idivl指令，

[xskxzr]

【译制】每个 C 程序员都应知道的关于未定义行为的那点事