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Because missing end delimitors are error prone and often viewed as a mistake, this approach is not recommended for commenting out code.

Compliant Solution (

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Preprocessor)

Instead of using /* and */ to comment out blocks of code, comment out blocks of code using conditional compilation (e.g., #if, #ifdef, or #ifndef).

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The text inside a block of code commented out using #if, #ifdef, or #ifndef must still consist of valid preprocessing tokens. This means that the characters " and ' must each be paired just as in real C code, and the pairs must not cross line boundaries. In particular, an apostrophe within a contracted word looks like the beginning of a character constant. Consequently, natural-language comments and pseudocode should always be written between the comment delimiters /* and */ or following //.

Compliant Solution (

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Compiler)

This compliant solution takes advantage of the compiler's ability to remove unreachable (dead) code. The code inside the if block must remain acceptable to the compiler. If other parts of the program such as macros, types, or function prototypes change later in a way that would cause syntax errors, the unexecuted code must be brought up to date to correct the problem. Then, if it is needed again in the future, all that must be done is to remove the surrounding if statement and the NOTREACHED comment.

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This is an instance of exception MSC07-EX2 to guideline MSC07-C. Detect and remove dead code.

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Automated Detection

The LDRA tool suite V 7.6.0 can detect violations of this recommendation.

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Tool	Version	Checker	Description
Section LDRA tool suite	Include Page c:LDRA_V c:LDRA_V
Section GCC	Include Page c:GCC_V c:GCC_V		Section can detect violations of this rule when the -Wcomment flag is used

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Related Vulnerabilities

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

Other Languages

Related Guidelines

This rule appears in the C++ Secure Coding Standard as : MSC04-CPP. Use comments consistently and in a readable fashion.

Bibliography

\[[ISO/IEC 9899:1999|AA. Bibliography#ISO/IEC 9899-1999]\] Section 6.4.9, "Comments," and Section 6.10.1, "Conditional inclusion"
\[[MISRA 04|AA. Bibliography#MISRA 04]\] Rule 2.2, "Source code shall only use /\* ... \*/ style comments," Rule 2.3, "The character sequence /\* shall not be used within a comment," and Rule 2.4, "Sections of code should not be "commented out"
\[[Summit 05|AA. Bibliography#Summit 05]\] [Question 11.19|http://c-faq.com/ansi/ifdefsyntax.html]

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