CODEWITHSUNDEEP
c++exceptionnamespaces
meddle0106
meddle0106

Reputation: 1292

namespace called 'exception' leads to compile problems

I have a problem with a namespace called "exception"

Let's consider following example header:

#include <exception>

namespace exception
{
  struct MyException : public std::exception
  {};
}


struct AnotherException : public exception::MyException
{
    AnotherException() : exception::MyException() { }
};

This header does not compile with following error:


    namespacetest.hpp: In constructor 'AnotherException::AnotherException()':
    namespacetest.hpp:12:48: error: expected class-name before '(' token
    namespacetest.hpp:12:48: error: expected '{' before '(' token

There are two solutions for this:

1) qualify namespace with "::" in line 12

AnotherException() : ::exception::MyException() { }

2) Rename namespace to e.g. "exceptional"

What is the reason, that the namespace "exceptions" leads to confusion? I know that there is a class std::exception. Does this cause the trouble?

Upvotes: 17

Views: 859

Answers (2)

Mark Garcia
Mark Garcia

Reputation: 17708

+1 to @Mike Seymour's answer! As a supplement, there are better ways than your current solution to prevent the ambiguity:

Just use MyException, without any namespace qualification:

struct AnotherException : public exception::MyException
{
    AnotherException() : MyException() { }
};

LIVE EXAMPLE

Or use C++11's inherited constructors feature:

struct AnotherException : public exception::MyException
{
    using MyException::MyException;
};

LIVE EXAMPLE

Upvotes: 10

Mike Seymour
Mike Seymour

Reputation: 254691

I know that there is a class std::exception. Does this cause the trouble?

Yes. Within std::exception, the unqualified name exception is the injected class name. This is inherited so, within your class, an unqualified exception refers to that, not your namespace.

Upvotes: 22

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