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According to the The C++ Standard, [except.spec], paragraph 8 [ISO/IEC 14882-2014], states the following:

A function is said to allow an exception of type E if the constant-expression in its noexcept-specification evaluates to false or its dynamic-exception-specification contains a type T for which a handler of type T would be a match (15.3) for an exception of type E.

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In this noncompliant code example, a function is declared as nonthrowing, but it is possible for std::vector::resize() to throw an exception when the requested memory cannot be allocated.

#include <cstddef>
#include <vector>
 
void f(std::vector<int> &v, size_t s) noexcept(true) {
  v.resize(s); // May throw 
}

Compliant Solution

In this compliant solution, the function's noexcept-specification is removed, signifying that the function allows all exceptions.

#include <cstddef>
#include <vector>

void f(std::vector<int> &v, size_t s) {
  v.resize(s); // May throw, but that is okay
}

Noncompliant Code Example

In this noncompliant code example, the second function claims to throw only exception1 Exception1, but it may also throw exception2: Exception2.

#include <exception>
 
class exception1Exception1 : public std::exception {};
class exception2Exception2 : public std::exception {};

void foo() {
  throw exception2Exception2{}; // Okay because foo() promises nothing about exceptions
}

void bar() throw (exception1Exception1) {
  foo();    // Bad because foo() can throw exception2Exception2
}

Compliant Solution

This compliant solution catches the exceptions thrown by foo():.

#include <exception>
 
class Exception1 : public std::exception {};
class Exception2 : public std::exception {};

void foo() {
  throw Exception2{}; // Okay because foo() promises nothing about exceptions
}

void bar() throw (exception1Exception1) {
  try {
    foo();
  } catch (exception2Exception2 e) {
    // Handle error without rethrowing it
  }
}

Compliant Solution

This compliant solution declares an a dynamic exception-specification for bar(), which covers all of the exceptions that can be thrown from it:.

void bar() throw (exception1, exception2) {
  foo();
}

Noncompliant Code Example

In this noncompliant code example, a function is declared as nonthrowing, but it is possible for std::vector::resize() to throw an exception when the requested memory cannot be allocated:

#include <vector>
 
void f(std::vector<int> &v, size_t s) noexcept(true) {
  v.resize(s); // May throw 
}

Compliant Solution

In this compliant solution, the function's noexcept-specification is removed, signifying that the function allows all exceptions:

#include <vector>

void f(std::vector<int> &v, size_t s) {
  v.resize(s); // May throw, but that is okay#include <exception>
 
class Exception1 : public std::exception {};
class Exception2 : public std::exception {};

void foo() {
  throw Exception2{}; // Okay because foo() promises nothing about exceptions
}

void bar() throw (Exception1, Exception2) {
  foo();
}

Implementation Details

Some vendors provide language extensions for specifying whether or not a function throws. For instance, Microsoft Visual Studio provides __declspec(nothrow)), and Clang supports __attribute__((nothrow)). Currently, the vendors do not document the behavior of specifying a nonthrowing function using these extensions. Throwing from a function declared with one of these language extensions is presumed to be undefined behavior.

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Throwing unexpected exceptions disrupts control flow and can cause premature termination and denial of service.

Automated Detection

Related Vulnerabilities

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

Related Guidelines

Bibliography

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