最奇怪的问题...... [英] The strangest problem....
问题描述
嗨我有：
unsigned int myvalue = 0;
unsigned char mytest = 0;
mytest = 0x34 ;
myvalue = mytest<<< 24;
然后myvalue得到值0x1A000000 !!!!!
怎么样这可能吗？不应该是0x34000000 ???
最好的问候
Jannick
Hi I have:
unsigned int myvalue=0;
unsigned char mytest=0;
mytest=0x34;
myvalue = mytest<<24;
Then myvalue gets the value 0x1A000000!!!!!
How is this possible? Should''nt it be 0x34000000???
Best Regards
Jannick
推荐答案
" Jannick" < Ja*@janse.dk>在消息中写道
news：bm ********** @ news.net.uni-c.dk ...
"Jannick" <Ja*@janse.dk> wrote in message
news:bm**********@news.net.uni-c.dk...
嗨我有：
unsigned int myvalue = 0;
unsigned char mytest = 0;
mytest = 0x34;
myvalue = mytest<< 24;
然后myvalue得到值0x1A000000 !!!!!
这怎么可能？不应该是0x34000000 ???
最好的问候
Jannick
Hi I have:
unsigned int myvalue=0;
unsigned char mytest=0;
mytest=0x34;
myvalue = mytest<<24;
Then myvalue gets the value 0x1A000000!!!!!
How is this possible? Should''nt it be 0x34000000???
Best Regards
Jannick
你确定，它的不是你节目中的拼写错误？ 0x1A000000是0x34<< 23
Allan
Are you sure, its not a typo in your program? 0x1A000000 is 0x34<<23
Allan
" Jannick" < Ja*@janse.dk> schrieb im Newsbeitrag
news：bm ********** @ news.net.uni-c.dk ...
"Jannick" <Ja*@janse.dk> schrieb im Newsbeitrag
news:bm**********@news.net.uni-c.dk...
嗨我有：
unsigned int myvalue = 0;
unsigned char mytest = 0;
mytest = 0x34;
myvalue = mytest<< 24;
然后myvalue得到值0x1A000000 !!!!!
这怎么可能？不应该是0x34000000 ???
Hi I have:
unsigned int myvalue=0;
unsigned char mytest=0;
mytest=0x34;
myvalue = mytest<<24;
Then myvalue gets the value 0x1A000000!!!!!
How is this possible? Should''nt it be 0x34000000???
是的，它应该（并且在我的系统上，当然不能证明
任何东西）。
来自标准的
：
" 4 E1的结果<< E2是E1左移E2位位置;腾出的位
用零填充。如果E1具有无符号类型，则结果的值
为E1 x 2 ^ E2，比结果类型中可表示的最大值
减少一个模数。如果E1具有签名类型和非负值，并且E1 x
2 ^ E2在结果类型中可表示，那么这就是结果值;
否则，行为未定义。
我唯一的解释 - 除了你的
实际代码中的拼写错误（23而不是24），代码中的其他内容导致UB。我无法想象，
你的编译器在某种程度上被打破了。
你能发布一个显示错误的最小_compilable_程序吗？
Robert
Yes, it should (and is on my system, which of course doesn''t proof
anything).
from the standard:
"4 The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits
are filled with zeros. If E1 has an unsigned type, the value of the result
is E1 x 2^E2, reduced modulo one more than the maximum value representable
in the result type. If E1 has a signed type and nonnegative value, and E1 x
2^E2 is representable in the result type, then that is the resulting value;
otherwise, the behavior is undefined."
The only explanation I have - besides a typo (23 instead of 24) in your
actual code is something else in the code causing UB. I can''t imagine, that
your compiler is broken in _such_ a way.
Can you post a minimum _compilable_ program which exhibits the error?
Robert
也许你的编译器操作系统
我的VC + win32是对的，
myvalue = 0x34
" Jannick" < Ja*@janse.dk>在消息中写道
news：bm ********** @ news.net.uni-c.dk ...
maybe your compiler os OS
my VC+win32 is right,
myvalue=0x34
"Jannick" <Ja*@janse.dk> wrote in message
news:bm**********@news.net.uni-c.dk...
嗨我有：
unsigned int myvalue = 0;
unsigned char mytest = 0;
mytest = 0x34;
myvalue = mytest<< 24;
然后myvalue得到值0x1A000000 !!!!!
这怎么可能？不应该是0x34000000 ???
最好的问候
Jannick
Hi I have:
unsigned int myvalue=0;
unsigned char mytest=0;
mytest=0x34;
myvalue = mytest<<24;
Then myvalue gets the value 0x1A000000!!!!!
How is this possible? Should''nt it be 0x34000000???
Best Regards
Jannick
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