Programming Forums > Application Development > C++

kurt · Jul 3rd, 2008, 11:07 AM

Let's say I have a function that all it's parameter have default values.

So, is there a performance difference between:

func( );
func(1, 2, 3);

Does it save the need to copy the values of the parameters when the function is called?

By the way, I set the default values to member variables.

Overloading is an option, but the only difference is to use overidden parameter values (vs) using member variables.

lectricpharaoh · Jul 3rd, 2008, 3:50 PM

Default parameter values are just a shorthand notation. The compiler will generate the appropriate default value and pass it, just as if you'd called the function with the default value. In other words, it compiles to the same object code.

Also, be aware that using default values can sometimes lead to ambiguity over which function to call if you're using overloading, so you need to keep this in mind, as it may be an issue:

(Toggle Plain Text)

void foo(int bar = 1);
void foo(void);
  .
  .
foo();  // which function is being called?

Jul 3rd, 2008, 11:07 AM	#1
kurt Programmer Join Date: Oct 2005 Posts: 68 Rep Power: 3	Function Default Values efficient? Let's say I have a function that all it's parameter have default values. So, is there a performance difference between: func( ); func(1, 2, 3); Does it save the need to copy the values of the parameters when the function is called? By the way, I set the default values to member variables. Overloading is an option, but the only difference is to use overidden parameter values (vs) using member variables.

Jul 3rd, 2008, 3:50 PM	#2
lectricpharaoh Caffeinated Neural Net Join Date: Jun 2005 Location: Dry west coast of Canada Posts: 1,033 Rep Power: 5	Re: Function Default Values efficient? Default parameter values are just a shorthand notation. The compiler will generate the appropriate default value and pass it, just as if you'd called the function with the default value. In other words, it compiles to the same object code. Also, be aware that using default values can sometimes lead to ambiguity over which function to call if you're using overloading, so you need to keep this in mind, as it may be an issue: (Toggle Plain Text) void foo(int bar = 1); void foo(void); . . foo(); // which function is being called? void foo(int bar = 1); void foo(void); . . foo(); // which function is being called? __________________ And once again, Probability proves itself willing to sneak into a back alley and service Drama as would a copper-piece harlot. - Vaarsuvius, Order of the Stick

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Programming Forums > Application Development > C++

Function Default Values efficient?