问题
Can I use default arguments in a constructor like this maybe
Soldier(int entyID, int hlth = 100, int exp = 10, string nme) : entityID(entyID = globalID++), health(hlth), experience(exp), name(nme = SelectRandomName(exp))
{ }
I want for example exp = 10 by default but be able to override this value if I supply it in the constructor otherwise it should use the default.
How can I do this, I know my approach does not work....
If I supply any value in the initialization list no matter whatever I supply in constructor gets overwritten ofcourse on the other hand whenever I supply a value in constructor then why do I need a default value in the first place as every time I am supplying a value for object initiation...?
Should I use different overloaded constructors or do you people have any other ideas....?
回答1:
Default arguments can only be supplied to a continuous range of parameters that extends to the end of the parameter list. Simply speaking, you can supply default arguments to 1, 2, 3, ... N last parameters of a function. You cannot supply default arguments to parameters in the middle of the parameter list, as you are trying to do above. Either rearrange your parameters (put hlth and exp at the end) or supply a default argument for nme as well.
Additionally, you constructor initializer list doesn't seem to make any sense. What was the point of passing entyID and nme from outside, if you override their values anyway in the constructor initializer list?
回答2:
All of the parameters with default arguments need to be after any required arguments. You should move the nme parameter before hlth.
回答3:
I believe you can do this, however, all your defaulted args would need to go at the end. So, in your example, the constructor signature would be
Soldier(int entyID, string nme, int hlth = 100, int exp = 10);
回答4:
Arguments with default values must be the last arguments in the function declaration. In other words, there can not be any arguments without default values following one with a default value.
回答5:
Only trailing arguments can be default arguments. You would need to give nme a default argument or change the order of the arguments that the constructor takes so that hlth and exp come last.
As regards the assignment you make in the initialiser list what happens there is that the member entityID gets assigned the value that is returned by the assignment of globalID++ to entyID which will be the value of entyID after the assignment. A similar thing happens for name.
来源：https://stackoverflow.com/questions/1634177/default-arguments-in-constructor