异常机制的模拟实现

在看韩老师的书《老码识途》。其中一章讲异常机制的实现探究。自己上手，先模拟一个。

实现的功能比较简单。

关键函数：

try_()

catch_( hdFunc handle )

finally_( hdFunc handle )

throw_( char *msg )

end_()

ps: typedef void (*hdFunc)( char *msg )

可以看到只能跑出一种错误类型，抛出一个字符串。

catch_()和finally_()必须在紧接在try_()后面调用。

原理就是用栈，每次catch_()和finally_()都会压栈。throw_则出栈，会调用所有的finally，但只会调用离栈顶最进的catch指定的处理函数。

包含 exception.h,stack.h,main.cpp

运行结果是：





下面是代码

stack.h:

[code] #ifndef __STACK_H__

#define __STACK_H__

#pragma once

#define MAXLEVEL 100

#define FLAG_CATCH 1

#define FLAG_FINALLY 2

#define FLAG_ERROR -1

#define EXIT_CODE 1

typedef void (*hdFunc)(char *);

struct s_exception

{

 int flag;

 hdFunc handle;

};

int gStackTop = 0;

s_exception gStack[MAXLEVEL];

s_exception fGetTop()

{

 //do not pop

 s_exception re;

 if( gStackTop <= 0 )

{

 //empty

 re.flag = FLAG_ERROR;

 return re;

}

 re = gStack[ gStackTop - 1 ];

 return re;

}

bool fPush( s_exception v )

{

 if( gStackTop >= MAXLEVEL )

 return false;

 gStack[ gStackTop ] = v;

 ++gStackTop;

 return true;

}

s_exception fPop()

{

 s_exception re;

 if( gStackTop <= 0 )

{

 //empty

 re.flag = FLAG_ERROR;

 return re;

}

 re = gStack[ --gStackTop ];

 return re;

}

#endif

[/code]

exception.h:

[code] #ifndef __EXCEPTION_H__

#define __EXCEPTION_H__

#pragma once

#include "stack.h"

#include <stdlib.h>

int gLvCnt = 0;

void try_()

{

 gLvCnt = 0;

}

void catch_( hdFunc handle )

{

 ++gLvCnt;

 s_exception ex;

 ex.flag = FLAG_CATCH;

 ex.handle = handle;

 fPush( ex );

}

void finally_( hdFunc handle )

{

 ++gLvCnt;

 s_exception ex;

 ex.flag = FLAG_FINALLY;

 ex.handle = handle;

 fPush( ex );

}

void end_()

{

 for( int i = 0;i < gLvCnt;++i )

 fPop();

}

void throw_( char *msg )

{

 //key function. throw exception upward

 while( true )

{

 s_exception ex = fPop();

 if( ex.flag == FLAG_FINALLY )

{

 ex.handle( msg );

}

 else if( ex.flag == FLAG_CATCH )//find it

{

 //终止模型。执行catch以后不恢复

 ex.handle( msg );

 while( ex.flag != FLAG_ERROR )

{

 if( ex.flag == FLAG_FINALLY )

 ex.handle( msg );

 ex = fPop();

}

 printf("ready to exit\n");

 system("pause");

 exit(0);//##

}

 else

{

 //error

 exit( EXIT_CODE );

}

}

}

#endif

[/code]

main.h:

[code] #include <stdio.h>

#include <assert.h>

#include "exception.h"

void ca( char *msg )

{

 printf("ca:%s\n",msg);

}

void cb( char *msg )

{

 printf("cb:%s\n",msg);

}

void cc( char *msg )

{

 printf("cc:%s\n",msg);

}

void fa( char *msg )

{

 printf("fa:%s\n",msg);

}

void fb( char *msg )

{

 printf("fb:%s\n",msg);

}

void cfc( char *msg )

{

 printf("cfc:%s\n",msg);

}

void fc( char *msg )

{

 try_();

 catch_( cfc );

 printf("fc:%s\n",msg);

 throw_( "error in fc" );

 end_();

}

void c()

{

 try_();

 finally_(fc);

 throw_( "error in c" );

 end_();

 assert( 0 );//never be to here

}

void b()

{

 try_();

 catch_( cb );

 c();

 end_();

}

void a()

{

 try_();

 catch_( ca );

 finally_( fa );

 b();

 end_();

}

int main()

{

 a();

 return 0;

}

[/code]