, dynamic_cast. . Visitor.
, , 2 7 dynamic_cast, . . nullptr:
class FilesystemEntry
{
//...
public:
//...
virtual File * asFile () { return nullptr; }
virtual Directory * asDirectory () { return nullptr; }
};
, . , - :
class File: public FilesystemEntry
{
//...
public:
//...
File * asFile () override { return this; }
};
class Directory: public FilesystemEntry
{
//...
public:
//...
Directory * asDirectory () override { return this; }
};
dynamic_cast:
FilesystemEntry * pEntry = new File(1.txt, 50);
File * pFile = pEntry-> asFile ();
assert(pFile);
(, SymbolicLink - ), FilesystemEntry .
Visitor (), . , visit, . - - .
, -. , :
:
, ;
(FilesystemEntry, File, Directory) ;
, - ;
, , SymbolicLink, , accept/visit :
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o accept SymbolicLink;
o visit ;
o -;
, .
. , . . , . .
.
:
- ;
- , , ;
- ;
- .
. try-catch:
try { -- -, , . ,.. }
catch ( ) { }
catch , catch, - terminate, - abort, .
. , - - .
= catch. :
try {
//
}
catch (int param) { cout << "int exception"; }
catch (char param) { cout << "char exception"; }
catch (...) { cout << "default exception"; }
, , () catch, -. , . :
● ;
● ;
● , ;
● , ;
● const ,
:
catch (...) =
{
std::cerr << Fatal error. Please contact [email protected] << std::endl; }
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O .
catch (...) catch( ) , , .. .
throw
try { throw 20;}, .
, .
- throw , . - . - .
. main runProgram, , . runProgram , main :
void runProgram ()
{
Try
{
ManagedIntegerArray a(10);
a[ rand() ] = 25;
}
catch (ManagedIntegerArray::IndexOutOfRange & e)
{
std::cout << Program has a problem with array index << std::endl;
}
}
int main ()
{
Try
{
runProgram();
}
catch (...)
{
std::cout << Program has some unknown problem << std::endl;
}
}
. catch , , .., terminate.
. catch , , . (rethrow), throw . :
void runProgram ()
{
Try
{
ManagedIntegerArray a(10);
a[ rand() ] = 25;
}
catch (ManagedIntegerArray::IndexOutOfRange & e)
{
//
std::cout << Program has a problem with array index << std::endl;
//
throw;
}
}
, ( throw ), termin
:
Try
{
throw new DerivedException(0, 0);
}
catch (DerivedException * _pE)
{
delete _pE;
}
-, , , . -, , , globalException. , .
- . , ( , ). , , - . , - , , , . , , , . , -.
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.. , , , std::exception.
std::exception <exception>. std::exception , . , :
● ;
● ;
● ;
● what(), C, .
what() .
:
● std::bad_alloc new, ;
● std::bad_cast dynamic_cast, , , ;
● std::bad_typeid typeid, ;
● std::out_of_range std::vector std::deque ;
● std::ios_base::failure / - , , exceptions, :
std::ifstream file;
file.exceptions (std::ifstream::failbit | std::ifstream::badbit);
std::logic_error std::runtime_error std::string, . , what() , .
std::logic_error , . , , . std::runtime_error, , , , . , -. , - - std::exception.
stack unwinding . . . . .
stack unwinding (, ).
, 2 :
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1. .
2. .
, , .
, .
:
void f ()
{
Date d1;
if (d1.GetDay() == 1)
throw std::runtime_error(Cannot call f() on the 1st day of the month);
Date d2(2013, 12, 23);
//...
}
, . d1 , d2 . stack unwinding , d1, d2.
. , , , f, d2, d1:
void f ()
{
Date d1;
if (d1.GetDay() == 1)
throw std::runtime_error(Cannot call f() on the 1st day of the month);
Date d2(2013, 12, 23);
//...
// Date::~Date(& d2);
// Date::~Date(& d1);
}
. , d1 , d2 , - , , , .
. 3 :
● 0 - ;
● 1 - d1, d2;
● 2 - d1 d2.
, (, 1 ), . , . .
, :
void f ()
{
Date * pDate = new Date();
Try
{
if (pDate->GetDay() == 1)
throw std::runtime_error(...);
//...
//
delete pDate;
}
catch (...)
{
//
delete pDate;
//
throw;
}
}
void g ()
{
FILE * file = fopen(test.txt, rt);
try
{
if (some_condition)
throw std::runtime_error(Condition failed);
//
//
fclose ( file );
}
catch (...)
{
//
fclose ( file );
//
throw;
}
}
, .
, , ., Date , :
Try
{
Date d1(2013, 14, 1); // 14
// :
// Date::~Date(& d1);
}
catch (...)
{
}
, , delete:
Try
{
Date * pDate = new Date(2013, 14, 1); // 14
// , delete
}
catch (...)
{
}
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, , . , .
. . , , , , stack unwinding, . , .
, std::uncaught_exception, , stack unwinding .
. catch ( catch ) , , . (rethrow), throw . :
void runProgram ()
{
Try
{
ManagedIntegerArray a(10);
a[ rand() ] = 25;
}
catch (ManagedIntegerArray::IndexOutOfRange & e)
{
//
std::cout << Program has a problem with array index << std::endl;
//
throw;
}
}
, , terminate ( abort, ).
