次のコードでは、メインの () に示されているように、2 つのケースで例外がスローされます。
#include <iostream>
// Our own exception classes - just for fun.
class myExceptionClassA
{
public:
myExceptionClassA () {std::cout << "\nWarning: Division by zero isn't allowed.\n";}
};
class myExceptionClassB
{
public:
myExceptionClassB () {std::cout << "\nWarning: Division by dividend isn't allowed.\n";}
};
class divisionClass
{
private:
int *result;
public:
divisionClass ()
{
// Allocating memory to the private variable.
result = new int;
}
/*
The class function `doDivide`:
1. Throws above defined exceptions on the specified cases.
2. Returns the division result.
*/
int doDivide (int toBeDividedBy) throw (myExceptionClassA, myExceptionClassB)
{
*result = 200000;
// If the divisor is 0, then throw an exception.
if (toBeDividedBy == 0)
{
throw myExceptionClassA ();
}
// If the divisor is same as dividend, then throw an exception.
else if (toBeDividedBy == *result)
{
throw myExceptionClassB ();
}
// The following code won't get executed if/when an exception is thrown.
std :: cout <<"\nException wasn't thrown. :)";
*result = *result / toBeDividedBy;
return *result;
}
~divisionClass ()
{
std::cout << "\ndddddddddd\n";
delete result;
}
};
int main ()
{
divisionClass obj;
try
{
obj.doDivide (200000);
}
catch (myExceptionClassA) {}
catch (myExceptionClassB) {}
try
{
obj.doDivide (3);
}
catch (myExceptionClassA) {}
catch (myExceptionClassB) {}
try
{
obj.doDivide (0);
}
catch (myExceptionClassA) {}
catch (myExceptionClassB) {}
try
{
obj.doDivide (4);
}
catch (myExceptionClassA) {}
catch (myExceptionClassB) {}
return 0;
}
- 両方の例外クラスの印刷ステートメントが印刷されます。
- デストラクタ内のステートメントは 1 回だけ出力されます。
- Valgrind はメモリ リークを示しません。
anisha@linux-y3pi:~/Desktop> g++ exceptionSafe3.cpp -Wall
anisha@linux-y3pi:~/Desktop> valgrind ./a.out
==18838== Memcheck, a memory error detector
==18838== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.
==18838== Using Valgrind-3.5.0 and LibVEX; rerun with -h for copyright info
==18838== Command: ./a.out
==18838==
Warning: Division by dividend isn't allowed.
Exception wasn't thrown. :)
Warning: Division by zero isn't allowed.
Exception wasn't thrown. :)
dddddddddd
==18838==
==18838== HEAP SUMMARY:
==18838== in use at exit: 0 bytes in 0 blocks
==18838== total heap usage: 3 allocs, 3 frees, 262 bytes allocated
==18838==
==18838== All heap blocks were freed -- no leaks are possible
==18838==
==18838== For counts of detected and suppressed errors, rerun with: -v
==18838== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 2 from 2)
anisha@linux-y3pi:~/Desktop>
デストラクタは 3 回呼び出されるべきではありませんか? 例外の場合は 2 回、return ステートメントの場合は 1 回です。
私が欠けている点を説明してください。
次に、main() の try catch ブロックをすべて削除してみました。
デストラクタはまったく呼び出されませんか?
anisha@linux-y3pi:~/Desktop> valgrind ./a.out
==18994== Memcheck, a memory error detector
==18994== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.
==18994== Using Valgrind-3.5.0 and LibVEX; rerun with -h for copyright info
==18994== Command: ./a.out
==18994==
Warning: Division by dividend isn't allowed.
terminate called after throwing an instance of 'myExceptionClassB'
==18994==
==18994== HEAP SUMMARY:
==18994== in use at exit: 133 bytes in 2 blocks
==18994== total heap usage: 3 allocs, 1 frees, 165 bytes allocated
==18994==
==18994== LEAK SUMMARY:
==18994== definitely lost: 0 bytes in 0 blocks
==18994== indirectly lost: 0 bytes in 0 blocks
==18994== possibly lost: 129 bytes in 1 blocks
==18994== still reachable: 4 bytes in 1 blocks
==18994== suppressed: 0 bytes in 0 blocks
==18994== Rerun with --leak-check=full to see details of leaked memory
==18994==
==18994== For counts of detected and suppressed errors, rerun with: -v
==18994== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 2 from 2)
Aborted
anisha@linux-y3pi:~/Desktop>