Re: Put variables into member variables or function variables?

"Jim Langston" <>
Fri, 21 Mar 2008 07:06:00 -0700
Andy Champ wrote:

Jim Langston wrote: wrote:

I modify my code into following sample code.
CTest is a class only constructed once when the device power on.
CTest::ExecuteRunState is a function entered periodically.
Do you think whether it is necessary to put the local variables into
class private members?
Otherwise, each time entering the ExecuteRunState(), those local
variables will be decleared and initionalized one time. It's a waste
of cpu resource.

class CTest

    void CTest(const CTest & m_CTest);
    void ExecuteRunState(); //This function will entered
 periodically };

void CTest::ExecuteRunState()

tMV measurement = 0;
tMVq quality = 0;
tMVt timeStamp = 0;

//Here those three variables will gain the newest values.
pData->GetNewestValue(&measurement, &quality, &timeStamp);

I don't think it's really necessary and is probably premature
optimization to do so. Global variables are generally frowned upon.
If the variables are only used inside the funciton ExecuteRunState,
then that's where they should be declared. Of course this presumes
that tMV, tMVq and tMVt have rather trivial constructors.

Given the concern on performance, and that GetNewestValue obviously
writes to them, why initialise them at all?

It is not necesarry to initialize them, but if they are classes or
structures they can have constructors anyway. For the given examples here
they are most likely trivial (int, float, etc..). But maybe tMV is some
class that when it is constructed reads data from a database for whatever
reason, then it is not trivial.

Just becasue you don't initialize a variable doesn't mean it doesn't have to
be constructed.

Jim Langston

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