Page History

Immutable objects should be {{const}}\-qualified.  Enforcing object immutability using {{const}}\-qualification helps ensure the correctness and security of applications.  ISO/IEC DTRTR 24772, for example, recommends labeling parameters as constant to avoid the unintentional modification of function arguments \[[ISO/IEC DTRTR 24772|AA. Bibliography#ISO/ISO/IEC DTR 24772]\]. See guidelinerecommendation [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 , still more become necessary. This phenomenon is sometimes called const poisoning, which can frequently lead to violations of guideline recommendation EXP05-C. Do not cast away a const qualification. While const qualification is a good idea, the costs may outweigh the value in the remediation of existing code.

Macros, or an enumeration constant, may also be used instead of a const-qualified object. Guideline Reocmmendation 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.

...

#ifndef SOME_HEADER_H
#define SOME_HEADER_H
...  // content of header file
#endif

See guideline recommendation PRE06-C. Enclose header files in an inclusion guard for more information on inclusion guards.

...

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

Related Guidelines

CERT C++ Secure Coding Standard: DCL00-CPP. Const-qualify immutable objects

This rule appears in the Java The CERT Oracle Secure Coding Standard as for Java: DCL04-J. Declare mathematical constants as static and final

ISO/IEC 9899:1999 Section 6.7.3, "Type qualifiers"

Bibliography

\[[Dewhurst 2002|AA. Bibliography#Dewhurst 02]\] Gotcha #25, "#define Literals"
\[[ISO/IEC 9899:1999|AA. Bibliography#ISO/IEC 9899-1999]\] Section 6.7.3, "Type qualifiers"
\[[Saks 2000|AA. Bibliography#Saks 00]\]

...