High Integrity C++ Coding Standard

15.1 Throwing an Exception

15.1.1 Only use instances of std::exception for exceptions

Exceptions pass information up the call stack to a point where error handling can be performed. If an object of class type is thrown, the class type itself serves to document the cause of an exception. Only types that inherit from std::exception, should be thrown.

#include <cstdint>
#include <stdexcept>
#include <iostream>
               
int foo ();
               
void bar ()
{
try
{
if (0 == foo ())
{
throw -1;     // @@- Non-Compliant [email protected]@
}
}
catch (int32_t e) // @@- Non-Compliant [email protected]@
{
}
                 
try
{
if (0 == foo ())
{
throw std::runtime_error ("unexpected condition"); // @@+ Compliant [email protected]@
}
}
catch (std::exception const & e)                       // @@+ Compliant [email protected]@
{
std::cerr << e.what ();
}
}

If an instance of an object inheriting from std::exception is created, then such an object must appear in a throw expression.

#include <exception>
               
class MyException : public std::exception
{
// ...
};
   
void f1 ()
{
MyException myExcp;   // @@- Non-Compliant [email protected]@
}
   
void f2 ()
{
MyException myExcp;   // @@+ Compliant [email protected]@
throw myExcp;
}

References

• HIC++ v3.3 – 9.2

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15.2 Constructors and Destructors

15.2.1 Do not throw an exception from a destructor

The 2011 C++ language standard states that unless a user provided destructor has an explicit exception specification, one will be added implicitly, matching the one that an implicit destructor for the type would have received.

#include <stdexcept>
class A
{
public:
~A ()        // @@- Non-Compliant: Implicit destructor for A would be declared with [email protected]@
             // @@-   noexcept, therefore this destructor is noexcept [email protected]@
{
throw std::runtime_error ("results in call to std::terminate");
}
};

Furthermore when an exception is thrown, stack unwinding will call the destructors of all objects with automatic storage duration still in scope up to the location where the exception is eventually caught. The program will immediately terminate should another exception be thrown from a destructor of one of these objects.

#include <cstdint>
#include <stdexcept>
               
class A
{
public:
A () : m_p () {}
               
~A () noexcept(false)
{
if (nullptr == m_p)
{
throw std::runtime_error ("null pointer in A"); // @@- Non-Compliant [email protected]@
}
}
                 
private:
int32_t * m_p;
};
               
void foo (int32_t i)
{
if (i < 0)
{
throw std::range_error ("i is negative");
}
}
               
void bar ()
{
try 
{
A a;
                   
foo (-1);
}
catch (std::exception const & e)
{
}
}

References

• HIC++ v3.3 – 9.1

View references >

15.3 Handling an Exception

15.3.1 Do not access non-static members from a catch handler of constructor/destructor function try block

When a constructor or a destructor has a function try block, accessing a non-static member from an associated exception handler will result in undefined behavior.

#include <cstdint>
               
class C
{
public:
C ();
               
private:
int32_t m_i;
};
               
C::C ()
try : m_i()
{
// constructor body
++m_i; // @@+ Compliant [email protected]@
}
catch (...)
{
--m_i; // @@- Non-Compliant [email protected]@
}

References

• MISRA C++:2008 – 15-3-3

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15.3.2 Ensure that a program does not result in a call to std::terminate

The path of an exception should be logical and well defined. Throwing an exception that is never subsequently caught, or attempting to rethrow when an exception is not being handled is an indicator of a problem with the design.

bool f1 ();
   
void f2 ()
{
throw;
}
   
void f3 ()
{
try
{
if (f1 ())
{
throw float(0.0);
}
else
{
f2();                // @@- Non-Compliant: No current exception [email protected]@
}
}
catch (...)
{
f2();  
}
}
   
int main ()
{
f3();                // @@- Non-Compliant: If 'float' thrown [email protected]@
}

References

• MISRA C++:2008 – 15-3-2

View references >