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This recommendation is related to guideline MSC12-C. Detect and remove code that has no effect.

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This noncompliant code example demonstrates how dead code can be introduced into a program \[[Fortify 062006|AA. Bibliography#Fortify 06]\]. The second conditional statement, {{if (s)}}, will never evaluate true because it requires that {{s}} not be assigned {{NULL}}, and the only path where {{s}} can be assigned a non\-{{NULL}} value ends with a return statement.

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MSC07-EX1: In some situations, dead code may make software resilient to future changes. An example of this is adding a default case to a switch statement even when all possible switch labels are specified. (see See guideline MSC01-C. Strive for logical completeness for an illustration of this example). .)

MSC07-EX2: It is also permissible to temporarily remove code that may be needed later. (see See guideline MSC04-C. Use comments consistently and in a readable fashion for an illustration.).

Risk Assessment

The presence of dead code may indicate logic errors that can lead to unintended program behavior. The ways in which dead code can be introduced into a program and the effort required to remove it can be complex. As a result, resolving dead code can be an in-depth process requiring significant analysis.

Automated Detection

The LDRA tool suite Version 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 Splint	Include Page c:Splint_V c:Splint_V		Section can detect violations of this recommendation

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when the -Wunreachable-code flag is used
Section GCC	Include Page c:GCC_V c:GCC_V		Section can detect violations of this recommendation when the -Wunreachable-code flag is used

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Section Klocwork	Include Page c:Klocwork_V c:Klocwork_V	Section LV_UNUSED.GEN

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VA_UNUSED.*

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UNREACH.*

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Section Coverity Prevent	Include Page c:Coverity_V c:Coverity_V	Section DEADCODE	Section can detect the specific instance where Code can never be reached because of a logical contradiction or a dead 'default' in switch statement

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Section Coverity Prevent	Include Page c:Coverity_V c:Coverity_V	Section UNREACHABLE	Section can detect the instances where Code block is unreachable because of the syntactic structure of the code

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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 : MSC07-CPP. Detect and remove dead code.

Bibliography

\[[Fortify 062006|AA. Bibliography#Fortify 06]\] Code Quality, "Dead Code"
\[[ISO/IEC PDTR 24772|AA. Bibliography#ISO/IEC PDTR 24772]\] "BRS Leveraging human experience," "BVQ Unspecified Functionality," and "XYQ Dead and Deactivated Code"
\[[MISRA 042004|AA. Bibliography#MISRA 04]\] Rule 2.4
\[[MITRE 072007|AA. Bibliography#MITRE 07]\] [CWE ID 561|http://cwe.mitre.org/data/definitions/561.html], "Dead Code"

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