Qt-Autosar-A26.5.2

Random number engines shall not be default-initialized

Required inputs: IR

Certain classes (particularly random number engines) should not be default-constructed without arguments. Random engines need proper seeding to generate meaningful random sequences. Default construction often results in predictable or poor-quality sequences with seeds that produce biased distributions. Explicitly provide a seed or use a seed source.

Bad code (default-constructed random engine):

std::mt19937 engine;               // ERROR: default seed, predictable sequence
int value = engine();              // Poor quality random numbers

Good code (seeded random engine):

std::random_device rd;
std::array<int, std::mt19937::state_size> seed_data;
std::generate_n(seed_data.data(), seed_data.size(), std::ref(rd));
std::seed_seq seq(std::begin(seed_data), std::end(seed_data));
std::mt19937 engine(seq);          // OK: properly seeded with random device
int value = engine();              // Good quality random numbers

Good code (using std::seed_seq):

std::seed_seq seed{1, 2, 3, 4, 5};
std::mt19937 engine(seed);         // OK: explicit seed sequence

Possible Messages

Key	Text	Severity	Disabled
forbidden_default_constructor_call	Call to forbidden default constructor.	None	False

Options

• This rule shares the following common options: exclude_in_macros, exclude_messages_in_system_headers, excludes, extend_exclude_to_macro_invocations, includes, justification_checker, languages, post_processing, provider, report_at, severity

• The following places define options that affect this rule: Stylechecks, Analysis-GlobalOptions

blacklist

blacklist

Type: set[bauhaus.analysis.config.QualifiedName]

Default: {'std::default_random_engine', 'std::knuth_b', 'std::linear_congruential_engine', 'std::mersenne_twister_engine', 'std::minstd_rand0', 'std::mt19937', 'std::mt19937_64', 'std::ranlux24', 'std::ranlux24_baset', 'std::ranlux48', 'std::ranlux48_base', 'std::subtract_with_carry_engine'}

Set of forbidden class names where calling the default constructor is forbidden.