CertC-DCL00¶
Const-qualify immutable objects
Required inputs: IR
Immutable objects should be
const-qualified. Enforcing object immutability using
const qualification helps ensure the correctness and security of
applications. ISO/IEC TR 24772, for example, recommends labeling parameters as
constant to avoid the unintentional modification of function arguments [
ISO/IEC
TR 24772].
STR05-C.
Use pointers to const when referring to string literals describes a
specialized case of this recommendation.
Adding
const qualification may propagate through a program; as you add
const, qualifiers become still more necessary. This phenomenon is
sometimes called
const poisoning, which can frequently lead to violations of
EXP05-C.
Do not cast away a const qualification. Although
const qualification is a good idea, the costs may outweigh the
value in the remediation of existing code.
A macro or an enumeration constant may also be used instead of a
const-qualified object.
DCL06-C.
Use meaningful symbolic constants to represent literal values describes the
relative merits of using
const-qualified objects, enumeration constants, and object-like
macros. However, adding a
const qualifier to an existing variable is a better first step
than replacing the variable with an enumeration constant or macro because the
compiler will issue warnings on any code that changes your
const-qualified variable. Once you have verified that a
const-qualified variable is not changed by any code, you may
consider changing it to an enumeration constant or macro, as best fits your
design.
Noncompliant Code Example
In this noncompliant code,
pi is declared as a
float. Although pi is a mathematical constant, its value is not
protected from accidental modification.
float pi = 3.14159f; float degrees; float radians; /* ... */ radians = degrees * pi / 180;
Compliant Solution
In this compliant solution,
pi is declared as a
const-qualified object:
const float pi = 3.14159f; float degrees; float radians; /* ... */ radians = degrees * pi / 180;
Risk Assessment
Failing to
const-qualify immutable objects can result in a constant being
modified at runtime.
| Recommendation | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
| DCL00-C | Low | Unlikely | High | P1 | L3 |
Related Guidelines
| SEI CERT C++ Coding Standard | VOID DCL00-CPP. Const-qualify immutable objects |
Bibliography
| [ Dewhurst 2002] | Gotcha #25, "#define Literals" |
| [ Saks 2000] |
Possible Messages
Key |
Text |
Severity |
Disabled |
|---|---|---|---|
parameter_missing_const |
A parameter which is not modified shall be const qualified. |
None |
False |
variable_missing_const |
A variable which is not modified shall be const qualified. |
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
ignore_pointer_variables¶
ignore_pointer_variables : bool = False
ignore_smart_pointer_variables¶
ignore_smart_pointer_variables : bool = False
only_check_unit_locals¶
only_check_unit_locals : bool = False
Note: this option is automatically activated during single-file analysis.
report_only_at_definition¶
report_only_at_definition : bool = False