Enums and exceptions in C++

[pazabo@gmail.com]

Hi,

I'm trying to create a class "Exception" that will contain some
enumeration specifying cause (why the exception was thrown):

class Exception {
public:
enum Type {
DATABASE_CORRUP TED,
COULD_NOT_READ_ TABLE_MAP
} type;

explicit Exception(Type type) : type(type) {}
};

But I don't really know how does the compiler understand:

throw Exception::COUL D_NOT_READ_TABL E_MAP

because it doesn't show any errors or even warnings, and
COULD_NOT_READ_ TABLE_MAP is not a member of Exception class. Does
anybody know how can this be correct ? Also I would be greatful if you
would share with me your experiences with C++ exceptions (do you create
a class for every situation or do you try to do it like I do / how do
you organize them).

Paul PAZABO Zaborski

[red floyd]

Re: Enums and exceptions in C++

pazabo@gmail.co m wrote:

Hi,
>
I'm trying to create a class "Exception" that will contain some
enumeration specifying cause (why the exception was thrown):
>
class Exception {
public:
enum Type {
DATABASE_CORRUP TED,
COULD_NOT_READ_ TABLE_MAP
} type;
>
explicit Exception(Type type) : type(type) {}
};
>
But I don't really know how does the compiler understand:
>
throw Exception::COUL D_NOT_READ_TABL E_MAP
>
because it doesn't show any errors or even warnings, and
COULD_NOT_READ_ TABLE_MAP is not a member of Exception class. Does
anybody know how can this be correct ? Also I would be greatful if you
would share with me your experiences with C++ exceptions (do you create
a class for every situation or do you try to do it like I do / how do
you organize them).
>

Actually, COULD_NOT_READ_ TABLE_MAP *is* a member of Exception. What
else would it be a member of? So it throws an Exception::Type .

However, if you're trying to throw an Exception, you'll need to do this:

throw Exception(Excep tion::COULD_NOT _READ_TABLE_MAP );

[Ondra Holub]

Re: Enums and exceptions in C++

pazabo@gmail.co m napsal:

Hi,
>
I'm trying to create a class "Exception" that will contain some
enumeration specifying cause (why the exception was thrown):
>
class Exception {
public:
enum Type {
DATABASE_CORRUP TED,
COULD_NOT_READ_ TABLE_MAP
} type;
>
explicit Exception(Type type) : type(type) {}
};
>
But I don't really know how does the compiler understand:
>
throw Exception::COUL D_NOT_READ_TABL E_MAP
>
because it doesn't show any errors or even warnings, and
COULD_NOT_READ_ TABLE_MAP is not a member of Exception class. Does
anybody know how can this be correct ? Also I would be greatful if you
would share with me your experiences with C++ exceptions (do you create
a class for every situation or do you try to do it like I do / how do
you organize them).
>
Paul PAZABO Zaborski

Try it this way:

class Exception {
public:
typedef enum {
DATABASE_CORRUP TED,
COULD_NOT_READ_ TABLE_MAP
} Type;

Type type_;

explicit Exception(Type type) : type_(type) {}

};

And then throw it this way:

throw Exception(DATAB ASE_CORRUPTED);

[pazabo@gmail.com]

Re: Enums and exceptions in C++



On Dec 5, 7:29 pm, red floyd <no.s...@here.d udewrote:

paz...@gmail.co m wrote:

Hi,

>

I'm trying to create a class "Exception" that will contain some
enumeration specifying cause (why the exception was thrown):

>

class Exception {
public:
enum Type {
DATABASE_CORRUP TED,
COULD_NOT_READ_ TABLE_MAP
} type;

>

explicit Exception(Type type) : type(type) {}
};

>

But I don't really know how does the compiler understand:

>

throw Exception::COUL D_NOT_READ_TABL E_MAP

>

because it doesn't show any errors or even warnings, and
COULD_NOT_READ_ TABLE_MAP is not a member of Exception class. Does
anybody know how can this be correct ? Also I would be greatful if you
would share with me your experiences with C++ exceptions (do you create
a class for every situation or do you try to do it like I do / how do
you organize them).Actually, COULD_NOT_READ_ TABLE_MAP *is* a member of Exception. What

else would it be a member of? So it throws an Exception::Type .
>
However, if you're trying to throw an Exception, you'll need to do this:
>
throw Exception(Excep tion::COULD_NOT _READ_TABLE_MAP );

Ok, thanks :)

Paul PAZABO Zaborski

[Salt_Peter]

Re: Enums and exceptions in C++


paz...@gmail.co m wrote:

Hi,
>
I'm trying to create a class "Exception" that will contain some
enumeration specifying cause (why the exception was thrown):
>
class Exception {
public:
enum Type {
DATABASE_CORRUP TED,
COULD_NOT_READ_ TABLE_MAP
} type;
>
explicit Exception(Type type) : type(type) {}
};
>
But I don't really know how does the compiler understand:
>
throw Exception::COUL D_NOT_READ_TABL E_MAP
>
because it doesn't show any errors or even warnings, and
COULD_NOT_READ_ TABLE_MAP is not a member of Exception class. Does
anybody know how can this be correct ? Also I would be greatful if you
would share with me your experiences with C++ exceptions (do you create
a class for every situation or do you try to do it like I do / how do
you organize them).
>
Paul PAZABO Zaborski

One suggestion might be to make your own exceptions by deriving from
std::exception.
Or alternately, by deriving from one of std::exception' s derivatives
like std::runtime_er ror.

That way, you can use a universal catch block to capture any
std::exception, including your own.
std::exception already has a virtual destructor and its already
equipped with a what() non-throwing member function. So its a very
simple construct (change the class names to your liking):

#include <iostream>
#include <ostream>
#include <stdexcept>

class db_corrupted_er ror : public std::runtime_er ror
{
public:
db_corrupted_er ror()
: std::runtime_er ror("database corrupted") { }
};

class read_table_erro r : public std::runtime_er ror
{
public:
read_table_erro r()
: std::runtime_er ror("read table map error") { }
};

int main()
{
try {

// do stuff
throw db_corrupted_er ror(); // testing

} catch ( const std::exception& r_e ) {
std::cerr << "error: " << r_e.what();
std::cerr << std::endl;
}
}

/*
error: database corrupted
*/

Another option is to derive from std::logic_erro r which is also a
derivative of std::exception.

[mlimber]

Re: Enums and exceptions in C++

Ondra Holub wrote:

Try it this way:
>
class Exception {
public:
typedef enum {
DATABASE_CORRUP TED,
COULD_NOT_READ_ TABLE_MAP
} Type;

This is C-style and is unnecessary in C++. Just do:

enum Type {
DATABASE_CORRUP TED,
COULD_NOT_READ_ TABLE_MAP
};

>
Type type_;
>
explicit Exception(Type type) : type_(type) {}
>
};
>
And then throw it this way:
>
throw Exception(DATAB ASE_CORRUPTED);

Of course you mean:

throw Exception(Excep tion::DATABASE_ CORRUPTED);

But see Salt Peter's advice elsethread.

Cheers! --M