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The variable declared by the exception-declaration, of type cv T or cv T&, is initialized from the exception object, of type E, as follows:
  — if T is a base class of E, the variable is copy-initialized from the corresponding base class subobject of the exception object;
  — otherwise, the variable is copy-initialized from the exception object.

Because the variable declared by the exception-declaration is copy-initialized, it is possible to slice the exception object as part of the copy operation, losing valuable exception information and leading to incorrect error recovery. For more information about object slicing, see OOP51-CPP. Do not slice derived objects. Further, if the copy constructor of the exception object throws an exception, the copy initialization of the exception-declaration object results in undefined behavior. (See ERR60-CPP. Exception objects must be nothrow copy constructible for more information.)

Always catch exceptions by lvalue reference unless the type is a trivial type. For reference, the C++ Standard, [basic.types], paragraph 9 [ISO/IEC 14882-2014], defines trivial types as the following:

Arithmetic types, enumeration types, pointer types, pointer to member types, std::nullptr_t, and cv-qualified versions of these types are collectively called scalar types.... Scalar types, trivial class types, arrays of such types and cv-qualified versions of these types are collectively called trivial types.

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Object slicing can result in abnormal program execution. This generally is not a problem for exceptions, but it can lead to unexpected behavior depending on the assumptions made by the exception handler.

Automated Detection

Related Vulnerabilities

Search for other vulnerabilities resulting from the violation of this rule on the CERT website.

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This rule is a subset of OOP51-CPP. Do not slice derived objects.

Bibliography

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