CertC++-ERR54ΒΆ

Catch handlers should order their parameter types from most derived to least derived

Required inputs: IR

The C++ Standard, [except.handle], paragraph 4 [ ISO/IEC 14882-2014], states the following:

The handlers for a try block are tried in order of appearance. That makes it possible to write handlers that can never be executed, for example by placing a handler for a derived class after a handler for a corresponding base class.

Consequently, if two handlers catch exceptions that are derived from the same base class (such as std::exception), the most derived exception must come first.

Noncompliant Code Example

In this noncompliant code example, the first handler catches all exceptions of class B, as well as exceptions of class D, since they are also of class B. Consequently, the second handler does not catch any exceptions. 

// Classes used for exception handling
class B {};
class D : public B {};

void f() {
  try {
    // ...
  } catch (B &b) {
    // ...
  } catch (D &d) {
    // ...
  }
}
Compliant Solution

In this compliant solution, the first handler catches all exceptions of class D, and the second handler catches all the other exceptions of class B. 

// Classes used for exception handling
class B {};
class D : public B {};

void f() {
  try {
    // ...
  } catch (D &d) {
    // ...
  } catch (B &b) {
    // ...
  }
}
Risk Assessment

Exception handlers with inverted priorities cause unexpected control flow when an exception of the derived type occurs.

Rule Severity Likelihood Remediation Cost Priority Level
ERR54-CPP Medium Likely Low P18 L1
Related Guidelines
[ MISRA 08] Rule 15-3-6 (Required)
Rule 15-3-7 (Required)
Bibliography
[ ISO/IEC 14882-2014] Subclause 15.3, "Handling an Exception"
Excerpt from SEI CERT C++ Coding Standard [https://cmu-sei.github.io/secure-coding-standards/sei-cert-cpp-coding-standard/rules/exceptions-and-error-handling-err/err54-cpp], Copyright (C) 1995-2026 Carnegie Mellon University. See section 9.4. "3rd-Party Licenses" in the documentation for full details.

Possible Messages

Key

Text

Severity

Disabled

catch_all_not_last

Catch-all shall occur as last handler.

None

False

wrong_catch_order

Catch handlers in wrong order.

None

False

Options