right shifting

C

crookie

if I have the foolowing code,

main()
{
unsigned int i=34;
i>>=32;
}

why does the value of i remain 34? I thought it should be a zero.
(the g++ compiler gives me a warning about shifting >= size of variable.)
 
K

Kai-Uwe Bux

crookie said:
if I have the foolowing code,

main()
{
unsigned int i=34;
i>>=32;
}

why does the value of i remain 34? I thought it should be a zero.
(the g++ compiler gives me a warning about shifting >= size of variable.)

The standard [5.8/1] says about the shift operators:

[...] The behavior is undefined if the right operand is negative, or
greater than or equal to the length in bits of the promoted left operand.

It would appear that on your platform sizeof(int)<=32, whence you have
undefined behavior: anything could happen.


Best

Kai-Uwe Bux
 
T

Thomas Tutone

crookie said:
if I have the foolowing code,

main()
{
unsigned int i=34;
i>>=32;
}

why does the value of i remain 34? I thought it should be a zero.
(the g++ compiler gives me a warning about shifting >= size of variable.)

Because on your system, an unsigned int has 32 or fewer bits, and (as I
recently learned) shifting by any number greater than or equal to the
number of bits is Undefined Behavior. Which means that any value of i
is equally valid.

For more detail, see this thread from over the summer:

http://tinyurl.com/y382v3

Best regards,

Tom
 

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments. After that, you can post your question and our members will help you out.

Ask a Question

Members online

No members online now.

Forum statistics

Threads
473,744
Messages
2,569,484
Members
44,903
Latest member
orderPeak8CBDGummies

Latest Threads

Top