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const keyword in functions

Posted on 2006-11-18
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Last Modified: 2010-04-01
Hi Experts,

when functions are declared with const parameters, I think I read it means it will  not be changed within that function.

functionOne( const string& a);    
functionTwo( const Test& t);
funcionThree(const bool c);

Are these always good idea when I am not going to change that parameter inside the function?

Also, functionOne(const string a)  is it going to be the same as functionOne(const string& a)
Other than that I am passing reference rather than value.

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Question by:ambuli
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3 Comments
 
LVL 9

Assisted Solution

by:DrAske
DrAske earned 400 total points
ID: 17973905
>>Are these always good idea when I am not going to change that parameter inside the function?
yes :)

>>Also, functionOne(const string a)  is it going to be the same as functionOne(const string& a)
regarding that *string* a will not change inside the function, *YES* it is.
but the first argument is passed by-value, and the other one is passed by-reference
(using  *&* depends on the size of the arguement)

NOTE!!
Many C++ programmers prefer that
1) Modifiable arguments be passed to functions by using pointers.
2) SMALL NONmodifiable arguments be passed by value.
3) HUGE (big) NONmodifiable arguments be passed by using REFERECES TO CONSTANTS.

regards,Ahmad;
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LVL 48

Accepted Solution

by:
AlexFM earned 600 total points
ID: 17973949
functionOne( const string& a);    
functionTwo( const Test& t);

These two functions get reference parameter. const definition ensures that parameters cannot be changed. Using const here is OK.

funcionThree(const bool c);
functionOne(const string a);

In this case using const doesn't make sence. Parameters are passed by value, this means, function operates with copy of these parameters. For caller, it doesn't matter whether such parameter is const or not - caller's parameter is not changed in any case.
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Author Comment

by:ambuli
ID: 17975706
Thank you.  Now, everything makes more sense :-)
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