no appropriate default constructor available

[denis_browne]

When writing the following code:

class Base
{
Base(const Base &rhs) {}
~Base();
};

void f() {
Base b;
};

The compiler shouts: no appropriate default constructor available

But when changing it to:

void f() {
Base b();
};

it compiles. Why?

 

[John Carson]

When writing the following code:

class Base
{
Base(const Base &rhs) {}
~Base();
};

void f() {
Base b;
};

The compiler shouts: no appropriate default constructor available

But when changing it to:

void f() {
Base b();
};

it compiles. Why?

Because in the second case you haven't declared an instance of Base. You
have instead declared a function that takes no arguments and returns a Base
object.

 

[Jakob Bieling]

When writing the following code:

class Base
{
Base(const Base &rhs) {}
~Base();
};

void f() {
Base b;
};

The compiler shouts: no appropriate default constructor available

But when changing it to:

void f() {
Base b();
};

it compiles. Why?

Base b(); declares a function 'b' taking no arguments and returning
an object of type 'Base'. Not so many days ago I read a nice 'rule of
thumb', if you may call it that: If it looks like a function
declaration, it is a function declaration. (Or something along the
lines)

hth

 

[n2xssvv g02gfr12930]

When writing the following code:

class Base
{
Base(const Base &rhs) {}
~Base();
};

void f() {
Base b;
};

The compiler shouts: no appropriate default constructor available

But when changing it to:

void f() {
Base b();
};

it compiles. Why?

The compiler is correct. A default constructor either takes no
parameters or has default values for all of the parameters, hence
enabling the default constructor call with no parameters or using the
already defined default parameters. Hence any one of the following is a
valid default constructor:

Base() { .... }
Base(int n = 7) { .... }
Base(char *name = NULL, unsigned id = 0) { .... }

JB