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各位老大，现有个作业题，小的不会，烦请大家帮个忙，脑袋想破也想不出来，请专家们赐教。谢谢了先！

eleven(周扒皮)

*Consider an ANSI compliant compiler on a machine using 2's
complement arithmetic for integers. The task is
to figure out whether a variable used for integers is signed or not.

One suggested solution is to write a macro like the following:

#define IS_UNSIGNED( var ) \
( (var) >= 0 && ~(var) >= 0 )

(a) Will this macro work for all possible integer values or are there
any exceptions? (If you find any exceptions,
you are encouraged to find a solution that will get rid of those
exceptions.)

(b) If the variable is a type instead of a variable, how would the
macro above be rewritten?

#define IS_UNSIGNED( TYPE ) \

(c) Is it possible to write a function to do this job instead of a
macro? If yes, show how the the macro shown
above can be rewritten as a function. If it cannot be cast as a
function, explain why not. [Either write below,
the IsVarUnsigned( ... ) function or give your reasoning.]

(#2786040@0)
Last Updated: 2006-2-16
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工作学习 / 专业技术讨论 / 各位老大，现有个作业题，小的不会，烦请大家帮个忙，脑袋想破也想不出来，请专家们赐教。谢谢了先！ -eleven(周扒皮); 2006-2-16 {952} (#2786040@0)
*Consider an ANSI compliant compiler on a machine using 2's
complement arithmetic for integers. The task is
to figure out whether a variable used for integers is signed or not.

One suggested solution is to write a macro like the following:

#define IS_UNSIGNED( var ) \
( (var) >= 0 && ~(var) >= 0 )

(a) Will this macro work for all possible integer values or are there
any exceptions? (If you find any exceptions,
you are encouraged to find a solution that will get rid of those
exceptions.)

(b) If the variable is a type instead of a variable, how would the
macro above be rewritten?

#define IS_UNSIGNED( TYPE ) \

(c) Is it possible to write a function to do this job instead of a
macro? If yes, show how the the macro shown
above can be rewritten as a function. If it cannot be cast as a
function, explain why not. [Either write below,
the IsVarUnsigned( ... ) function or give your reasoning.]

me try:) -frankwoo(柳五随风); 2006-2-16 {418} (#2786400@0)
1.#define ...
当你用int定义一个数值1时，出错，原因是以上的定义只能支持你以unsigned int定义的形式定义一个 var。
改进方法：

#define ISUNSIGNED(var) ( (var > 0x7fffffff)? (var& 0x80000000) : 1 ) //假设是32位系统，你要进一步改进的话，那就用sys/types.h里面的MAX..等把具体的数值替换了。

2。type的问题，不懂，我想不出来任何IS_UNSIGNED(unsigned int)这样的东西，将type 作为string处理时可以的，但是不满足你这里的需求。

谢谢。继续顶。 -eleven(周扒皮); 2006-2-16 (#2786487@0)

有什么奖励？ -canadiantire(轮胎-M.I.N.K.); 2006-2-16 (#2786502@0)
你确认你的type部分是这样描述的？ -frankwoo(柳五随风); 2006-2-16 (#2786510@0)

没错的，往type cast 上考虑。 -canadiantire(轮胎-M.I.N.K.); 2006-2-16 (#2786521@0)

type cast怎么cast一个type呢？typeid?，C里面有对应的东西吗？ -frankwoo(柳五随风); 2006-2-16 (#2786535@0)

parameter is the type -canadiantire(轮胎-M.I.N.K.); 2006-2-16 (#2786543@0)

呵呵，多谢轮胎：）#define IS_UNSIGNEDINT( type) ( (typeid(type) == typeid( unsigned int) ) 如何？ -frankwoo(柳五随风); 2006-2-16 (#2786559@0)

只见过typeof,没见过typeid. -canadiantire(轮胎-M.I.N.K.); 2006-2-16 (#2786577@0)

C++ -frankwoo(柳五随风); 2006-2-16 (#2786599@0)

such as (type)(-1) -iwantcar(EnjoyStudying); 2006-2-16 (#2786544@0)
有符号和没有符号的类型.用来转换数字,结果应该是不同的. -iwantcar(EnjoyStudying); 2006-2-16 (#2786550@0)

这样也行：） -frankwoo(柳五随风); 2006-2-16 (#2786563@0)

不过好像没有value嘛，怎么(type)..呀？ -frankwoo(柳五随风); 2006-2-16 (#2786567@0)

please think. I am tired. -iwantcar(EnjoyStudying); 2006-2-16 (#2786636@0)

扒皮，2出来了，不可以用function替换，因为type需要在compile的时候处理。你准备怎么意思一下呀？：） -frankwoo(柳五随风); 2006-2-16 (#2786566@0)

你的第一个还不如原来题里面那个呢。 -canadiantire(轮胎-M.I.N.K.); 2006-2-16 (#2786578@0)

指点一二？，谢谢：） -frankwoo(柳五随风); 2006-2-16 (#2786598@0)

int i=1; IS_SUNSIGNED(i)的结果是什么？ -canadiantire(轮胎-M.I.N.K.); 2006-2-16 (#2786607@0)

1<ox7FFFFFFFU, so 是1，true了。 -frankwoo(柳五随风); 2006-2-16 (#2786612@0)

int ! 不是unsigned int. -canadiantire(轮胎-M.I.N.K.); 2006-2-16 (#2786613@0)

明白你的意思了，不过我认为这里是要判断值是不是unsigned int，而不是类型定义的东西，或许我错了：）您有何高见？ -frankwoo(柳五随风); 2006-2-16 (#2786622@0)

int i =-1, ISUNSIGNED(i) 呢？ -canadiantire(轮胎-M.I.N.K.); 2006-2-16 (#2786632@0)
不明白你的那个宏到底是用来干吗的。 -canadiantire(轮胎-M.I.N.K.); 2006-2-16 (#2786638@0)

#define IS_UNSIGNED(var) ( ((var)>=0 && ~(var)>=0 ) || ( (var <= 0) &&~(var)<=0 ) )? 如何？ -frankwoo(柳五随风); 2006-2-16 (#2786656@0)

你先把这几个数挨个试一遍再贴：int i=0, 1, -1, unsigned int i=1, 0, ~0. -canadiantire(轮胎-M.I.N.K.); 2006-2-16 (#2786706@0)

多了两=,请教这里需要判断unsigned int非法定义吗？比如unsigned int i=-1是否合法？ -frankwoo(柳五随风); 2006-2-16 (#2786720@0)

不需要，1、如果非法compiler 会complain;2、unsigned int i=-1,不非法，是合法的付值语句，连警告都不是。 -canadiantire(轮胎-M.I.N.K.); 2006-2-16 (#2786750@0)

谢谢，那么原来的定义我没有看出来又什么问题，您高见如何？另外除了typeid和typeof以外，还有什么解决的办法? -frankwoo(柳五随风); 2006-2-16 (#2786754@0)

2 done. how to pay me? -iwantcar(EnjoyStudying); 2006-2-16 {103} (#2786721@0)
#include <stdio.h>

int main()
{
if ((unsigned int)(-1) > 2)
printf ("dd\n");
return 0;
}

有符号和没有符号的类型.用来转换数字,结果是不同的. -iwantcar(EnjoyStudying); 2006-2-16 (#2786725@0)

虚心请教你的2的macro怎么定义呢？ -frankwoo(柳五随风); 2006-2-16 (#2786829@0)

#define IS_UNSIGN(a) ((a)(-1) > 2) -iwantcar(EnjoyStudying); 2006-2-16 (#2786851@0)

厉害厉害，我还做不到信手拈来：） -frankwoo(柳五随风); 2006-2-16 (#2786871@0)

我再来：）， -frankwoo(柳五随风); 2006-2-16 {290} (#2786808@0)
1。没有什么问题。
2。#define IS_UNSIGNED(type) ( typeid(unsigned int) == typeid( type) )

test code
...
#include <typeinfo>
using namespace std;

#define ULONG unsigned long

...

if( IS_UNSIGNED(ULONG) )
.....

不能定义对应的function, 因为function不能在compiler的时候执行。

不建议你用typeid,因为 1、这个题在C++出现之前就有了；2、这很明显是个C的作业，typeid是个C++ keyword, C compiler 不认。 -canadiantire(轮胎-M.I.N.K.); 2006-2-16 (#2786840@0)

:),谢谢，老兄功力深厚呀：），佩服。 -frankwoo(柳五随风); 2006-2-16 (#2786861@0)

@Calgary

各位老大，现有个作业题，小的不会，烦请大家帮个忙，脑袋想破也想不出来，请专家们赐教。谢谢了先！

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@Calgary

各位老大，现有个作业题，小的不会， 烦请大家帮个忙，脑袋想破也想不出来，请专家们赐教。谢谢了先！

Replies, comments and Discussions:

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各位老大，现有个作业题，小的不会，烦请大家帮个忙，脑袋想破也想不出来，请专家们赐教。谢谢了先！