template based exception class

[Nick Keighley]

Hi,

Perhaps I was little ambitious with this template class.

When I define exception classes for packages I seemed to write code
similar to this each time:-

class DecompressionEr ror : public std::runtime_er ror
{
public:
DecompressionEr ror (const std::string& what = "")
: runtime_error(s td::string("Dec ompression Error ") + what)
{
}

virtual ~DecompressionE rror()
{
}
};


Any comments on the wisdom of such a class?

This looked like a good use for templates. Hence:-

#include <string>
#include <stdexcept>

template class<const char* NAMEclass Error: public std::runtime_er ror
// line 19
{
public:

Error (const std::string& what = "")
: runtime_error(s td::string(NAME ) + " Error ") + what)
{

}



virtual ~Error()
{

}

};


int main (void)
{
Error ("Pippo") pippo_x;

try
{
throw Error("Pippo");
}
catch (Error ("Pippo")& e)
{
cerr << e.what();
}
}


This actually crashed the compiler!

:\bin\error_tem pl.cpp(19) : fatal error C1001: INTERNAL COMPILER ERROR
(compiler file 'msc1.cpp', line 1188)
Please choose the Technical Support command on the Visual C++
Help menu, or open the Technical Support help file for more
information


So does my code look ok?


--
Nick Keighley

Programming should never be boring, because anything
mundane and repetitive should be done by the computer.
~Alan Turing

[Morten V Pedersen]

Re: template based exception class

Nick Keighley wrote:

Hi,
>
Perhaps I was little ambitious with this template class.
>
When I define exception classes for packages I seemed to write code
similar to this each time:-
>
class DecompressionEr ror : public std::runtime_er ror
{
public:
DecompressionEr ror (const std::string& what = "")
: runtime_error(s td::string("Dec ompression Error ") + what)
{
}
>
virtual ~DecompressionE rror()
{
}
};
>
>
Any comments on the wisdom of such a class?
>
This looked like a good use for templates. Hence:-
>
#include <string>
#include <stdexcept>
>
template class<const char* NAMEclass Error: public std::runtime_er ror
// line 19
{
public:
>
Error (const std::string& what = "")
: runtime_error(s td::string(NAME ) + " Error ") + what)
{
>
}
>
>
>
virtual ~Error()
{
>
}
>
};
>
>
int main (void)
{
Error ("Pippo") pippo_x;
>
try
{
throw Error("Pippo");
}
catch (Error ("Pippo")& e)
{
cerr << e.what();
}
}
>
>
This actually crashed the compiler!
>
:\bin\error_tem pl.cpp(19) : fatal error C1001: INTERNAL COMPILER ERROR
(compiler file 'msc1.cpp', line 1188)
Please choose the Technical Support command on the Visual C++
Help menu, or open the Technical Support help file for more
information
>
>
So does my code look ok?
>
>
--
Nick Keighley
>
Programming should never be boring, because anything
mundane and repetitive should be done by the computer.
~Alan Turing
>

Hi Nick,
I have a couple of quick comments to your code:
- Check: http://www.comeaucomputing.com/techt...#stringliteral
- template class<const char* NAME=template<c onst char* NAME>
- You also need to check you angle brackets vs. parantheses

// morten

[Stephane Wirtel]

Re: template based exception class

And why not:

#define STRINGIZE(x) XSTRING(x)
#define XSTRING(x) #x

#define DECLARE_EXCEPTI ON(name) \
class name##Exception : public std::runtime_er ror { \
public: \
name##Exception ( const std::string & what = "" ) \
: std::runtime_er ror( std::string(STR INGIZE(name) "Exception" ) + (
what.empty() ? std::string("") : std::string(" : ")) + what ) { \
} \
virtual ~name##Exceptio n() throw() { \
} \
}

DECLARE_EXCEPTI ON(My);
DECLARE_EXCEPTI ON(Super);

int main( int argc, char ** argv ) {
try {
throw MyException("Th ere is an error");
}
catch( const MyException & ex ) {
std::cerr << ex.what() << std::endl;
}
return 0;
}

--
Nick Keighley
>
Programming should never be boring, because anything
mundane and repetitive should be done by the computer.
~Alan Turing
>

[Nick Keighley]

Re: template based exception class

Stephane Wirtel wrote:

you snipped my original question

And why not:
>
#define STRINGIZE(x) XSTRING(x)
#define XSTRING(x) #x
>
#define DECLARE_EXCEPTI ON(name) \
class name##Exception : public std::runtime_er ror { \
public: \
name##Exception ( const std::string & what = "" ) \
: std::runtime_er ror( std::string(STR INGIZE(name) "Exception" ) + (
what.empty() ? std::string("") : std::string(" : ")) + what ) { \
} \
virtual ~name##Exceptio n() throw() { \
} \
}
>
DECLARE_EXCEPTI ON(My);
DECLARE_EXCEPTI ON(Super);
>
int main( int argc, char ** argv ) {
try {
throw MyException("Th ere is an error");
}
catch( const MyException & ex ) {
std::cerr << ex.what() << std::endl;
}
return 0;
}

yeah, I know I could have done that. But I thought the idea generally
was
to replace function type macros with templates.


--
Nick Keighley

[Stephane Wirtel]

Re: template based exception class

yeah, I know I could have done that. But I thought the idea generally

was
to replace function type macros with templates.

Why do you want to use the template for this case ?

The template parameters cannot be 'double' or 'char *'.

[Nick Keighley]

Re: template based exception class

Morten V Pedersen wrote:

Nick Keighley wrote:

Perhaps I was little ambitious with this template class.

When I define exception classes for packages I seemed to write code
similar to this each time:-

class DecompressionEr ror : public std::runtime_er ror
{
public:
DecompressionEr ror (const std::string& what = "")
: runtime_error(s td::string("Dec ompression Error ") + what)
{
}

virtual ~DecompressionE rror()
{
}
};


Any comments on the wisdom of such a class?

This looked like a good use for templates. Hence:-

#include <string>
#include <stdexcept>

template class<const char* NAMEclass Error: public std::runtime_er ror
// line 19
{
public:

Error (const std::string& what = "")
: runtime_error(s td::string(NAME ) + " Error ") + what)
{

}

virtual ~Error()
{

}
};


int main (void)
{
Error ("Pippo") pippo_x;

try
{
throw Error("Pippo");
}
catch (Error ("Pippo")& e)
{
cerr << e.what();
}
}


This actually crashed the compiler!

:\bin\error_tem pl.cpp(19) : fatal error C1001: INTERNAL COMPILER ERROR
(compiler file 'msc1.cpp', line 1188)
Please choose the Technical Support command on the Visual C++
Help menu, or open the Technical Support help file for more
information

I have a couple of quick comments to your code:
- Check: http://www.comeaucomputing.com/techt...#stringliteral

ah! and he became Enlightened

- template class<const char* NAME=template<c onst char* NAME>

I've no idea where that extra "class" came from...

- You also need to check you angle brackets vs. parantheses

sure do!

excellent! comp.lang.c++ is worth every penny I pay for it!

This code:-

*************** *************** *************** *************** ************
#include <string>
#include <stdexcept>
#include <iostream>

char x_name[] = "Pippo";


template <const char* NAMEclass Error: public std::runtime_er ror
{
public:

Error (const std::string& what = "")
: runtime_error(s td::string(NAME ) + " Error " + what)
{

}



virtual ~Error()
{

}

};


int main (void)
{
Error <x_namepippo_ x;

try
{
throw Error<x_name>(" frodo");
}
catch (Error <x_name>& e)
{
std::cerr << e.what();
}

return 0;
}

*************** *************** *************** *************** ************
produces this output:-
Pippo Error frodo


--
Nick Keighley

- I wanted to put a check in getGuiExtract() , but it's a void
method, inherited from the father of the father of the father of
the
father of the father of the father of the father of the father...

So I can't modify its interface.
[found in code comment]

[Nick Keighley]

Re: template based exception class

Stephane Wirtel wrote:

I tried to pass a string constant as a macro parameter. Stephane
suggested
a macro instead

yeah, I know I could have done that. But I thought the idea generally
was to replace function type macros with templates.

>
Why do you want to use the template for this case ?

to avoid writing the same code (admittedly not very much) over and over
again.

The template parameters cannot be 'double' or 'char *'.

why would I want it to be double? Why can't it be double. I agree
the template version looks so awkward I'll probably use the macro


--
Nick Keighley

[Stephane Wirtel]

Re: template based exception class

I tried to pass a string constant as a macro parameter. Stephane

suggested
a macro instead

There is a trick if you want to use 'char *' in the template parameter,
you can define a string as like as an 'extern char []'.

But you can get an error with this example:

extern const char hello [] = "hello";
extern const char world [] = "world";

the variable 'hello' and 'world' are const char [6] ( with '\0' )

my_template< hello template_hello;
my_template< world template_world;

for the compiler is the same type.

>The template parameters cannot be 'double' or 'char *'.

>
why would I want it to be double? Why can't it be double. I agree
the template version looks so awkward I'll probably use the macro

double and char * are the only cases where you can't use these types for a
template parameter.
If you are interested by the template, you can read "C++ Template : The
complete guide" of Vandervoorde & Josuttis.

Stephane

[jimmy]

Re: template based exception class


Nick Keighley 写道：

Morten V Pedersen wrote:

Nick Keighley wrote:

>

Perhaps I was little ambitious with this template class.
>
When I define exception classes for packages I seemed to write code
similar to this each time:-
>
class DecompressionEr ror : public std::runtime_er ror
{
public:
DecompressionEr ror (const std::string& what = "")
: runtime_error(s td::string("Dec ompression Error ") + what)
{
}
>
virtual ~DecompressionE rror()
{
}
};
>
>
Any comments on the wisdom of such a class?
>
This looked like a good use for templates. Hence:-
>
#include <string>
#include <stdexcept>
>
template class<const char* NAMEclass Error: public std::runtime_er ror
// line 19
{
public:
>
Error (const std::string& what = "")
: runtime_error(s td::string(NAME ) + " Error ") + what)
{
>
}
>
virtual ~Error()
{
>
}
};
>
>
int main (void)
{
Error ("Pippo") pippo_x;
>
try
{
throw Error("Pippo");
}
catch (Error ("Pippo")& e)
{
cerr << e.what();
}
}
>
>
This actually crashed the compiler!
>
:\bin\error_tem pl.cpp(19) : fatal error C1001: INTERNAL COMPILER ERROR
(compiler file 'msc1.cpp', line 1188)
Please choose the Technical Support command on the Visual C++
Help menu, or open the Technical Support help file for more
information

>
>

I have a couple of quick comments to your code:
- Check: http://www.comeaucomputing.com/techt...#stringliteral

>
ah! and he became Enlightened
>
>

- template class<const char* NAME=template<c onst char* NAME>

>
I've no idea where that extra "class" came from...
>

- You also need to check you angle brackets vs. parantheses

>
sure do!
>
excellent! comp.lang.c++ is worth every penny I pay for it!
>
This code:-
>
*************** *************** *************** *************** ************
#include <string>
#include <stdexcept>
#include <iostream>
>
char x_name[] = "Pippo";
>
>
template <const char* NAMEclass Error: public std::runtime_er ror
{
public:
>
Error (const std::string& what = "")
: runtime_error(s td::string(NAME ) + " Error " + what)
{
>
}
>
>
>
virtual ~Error()
{
>
}
>
};
>
>
int main (void)
{
Error <x_namepippo_ x;
>
try
{
throw Error<x_name>(" frodo");
}
catch (Error <x_name>& e)
{
std::cerr << e.what();
}
>
return 0;
}
>
*************** *************** *************** *************** ************
produces this output:-
Pippo Error frodo
>
>
--
Nick Keighley
>
- I wanted to put a check in getGuiExtract() , but it's a void
method, inherited from the father of the father of the father of
the
father of the father of the father of the father of the father...
>
So I can't modify its interface.
[found in code comment]

you simply go insane.