What is the proper way of defining a class that inherits from a base class
that has no constructor with 0 arguments?
The following code generates compiler error CS1501, "No overload for method
'BaseClass' takes '0' arguments".
class BaseClass
{
public BaseClass(doubl e x)
{
}
}
class TestClass : BaseClass
{
}
Inserting the constructor
public TestClass(doubl e x)
{
}
into TestClass still generates the same error. 3 1676
I think you want:
class TestClass : BaseClass {
public TestClass(doubl e x) : base(x)
{
// whatever
}
}
This is "constructo r chaining".
--
I may not always have the best answers, but at least I'm not posting
questions in the wrong newsgroups...
"G. Purby" <GP****@discuss ions.microsoft. com> wrote in message
news:E9******** *************** ***********@mic rosoft.com... What is the proper way of defining a class that inherits from a base class that has no constructor with 0 arguments?
The following code generates compiler error CS1501, "No overload for method 'BaseClass' takes '0' arguments".
class BaseClass { public BaseClass(doubl e x) { } }
class TestClass : BaseClass { }
Inserting the constructor
public TestClass(doubl e x) { }
into TestClass still generates the same error.
It goes something like this:
If you define a class without a constructor, then the compiler will
generate an implicit constructor that takes no arguments.
So, if you write:
class A
{
};
The compiler will generate:
class A
{
public A()
{
// does nothing.
}
}
However, if you define a class with a constructor, then the compiler
will NOT generate a default constructor for you.
So if you type:
class B
{
public B( double d )
{
// more code goes here.
}
}
The compiler will generate exactly that.
Suppose now that you want to inherit from B:
class C : B
{
public C()
{
// yet more code goes here.
}
}
Then the constructor for class C MUST call a constructor for class B.
Since you have not explicitly specified what constructir to call for
class B, the compiler will attempt to call a parametless constructor.
So, the compiler will TRY to generate:
class C : B
{
public C()
{
B();
}
}
But since you have already defined a constructor for class B, one that
DOES take a parameter, the compiler will not generate a default
parameterless constructor for B, and as such, the compilation will
fail.
To remedy this, either explicitly define a paramaterless constructor
for B, as follows:
class B
{
public B( double d )
{
// more code goes here.
}
public B()
{
// whatever.
}
}
Or, modify class C to explicitly call the constructor in class class B,
as follows:
class C : B
{
public C() : base(0.0)
{
// yet more code goes here.
}
}
Thank you, Mohammad. The way you have shown of defining a constructor with a
": base()" clause is exactly the feature I need. Problem solved.
What had originally confused me was that the compiler complained about a
wrong number of arguments, not a failure to invoke the base constructor. You
have made clear why it would do that. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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