Why "throw std::string" is not correct?

[Cheng Mo]

Below code cannot be compiled.
try
{
throw std::string;
}
catch(...)
{
}

While below is correct.
try
{
throw std::string();
}
catch(...)
{
}

Why doesn't standard C++ parse "throw std::string" as "throw
std::string()"?

 

[Sharad Kala]

Below code cannot be compiled.
try
{
throw std::string;

std::string is name of a class.

}
catch(...)
{
}

While below is correct.
try
{
throw std::string();

std::string() creates an unnamed object.

}
catch(...)
{
}

It's legal to throw an object but not a class name.

Why doesn't standard C++ parse "throw std::string" as "throw
std::string()"?

They are different. That's the way language is designed, for more queries
should help you.

Sharad

 

[Dietmar Kuehl]

Below code cannot be compiled.
throw std::string;

Throw takes an object as parameter, not a type.
'std::string' is a type, not an object.

While below is correct.
throw std::string();

'std::string()' is an object (of type 'std::string').

Why doesn't standard C++ parse "throw std::string" as "throw
std::string()"?

Why should it? There is a distinction between an object and
a type.