Re: GDB & static const variables
Re: GDB & static const variables
- Subject: Re: GDB & static const variables
- From: Eric Gorr <email@hidden>
- Date: Thu, 16 Jul 2009 12:39:11 -0400
On Jul 16, 2009, at 12:29 PM, Fritz Anderson wrote:
On 16 Jul 2009, at 10:25 AM, Eric Gorr wrote:
Boolean TestFunction( void )
{
static const int doubleByteDegreeMark = 42;
static int anotherVar = 12;
return ( doubleByteDegreeMark == 42 && anotherVar == 12 );
}
from GDB, if I do 'info locals' it prints out:
(gdb) info locals
anotherVar = 12
if I try to print out the value of doubleByteDegreeMark, it gives
me the error message:
(gdb) print doubleByteDegreeMark
No symbol "doubleByteDegreeMark" in current context.
So, my (probably really simple) question is how can I print out the
value of doubleByteDegreeMark from GDB?
Given that doubleByteDegreeMark is a constant, and referred to only
within the function, gcc optimized by doing away with the storage,
and substituted the literal value 42; and then it saw "42 == 42,"
and optimized that to true; and then saw "true && anotherVar == 12,"
and optimized that to "anotherVar == 12." I don't know why it didn't
optimize that to simply "true." Maybe at the optimization level you
chose, it didn't do the analysis to get that far.
There being no storage for doubleByteDegreeMark, gdb didn't have any
stored value to display. I don't know the details of why it didn't
know about it just as a constant; I've seen it display enum constants.
Thank you for your comments.
I still see the same problem if change the test function to:
Boolean TestFunction( int val )
{
static const int doubleByteDegreeMark = 42;
static int anotherVar = 12;
return ( val == doubleByteDegreeMark || val == anotherVar );
}
Now, I suppose it is still possible that the compiler will have simply
optimized this to:
Boolean TestFunction( int val )
{
static int anotherVar = 12;
return ( val == 42 || val == anotherVar );
}
or something.
This is the debug build with all optimizations turned off.
Under other circumstances, should 'info locals' display
doubleByteDegreeMark? Should I be able to print doubleByteDegreeMark?
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