SEI CERT C Coding Standard

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This recommendation is a specific case of MSC12-C. Detect and remove code that has no effect or is never executed.

Noncompliant Code Example

In this example, p2 is assigned the value returned by bar(), but that value is never used. Note this example assumes that foo() and bar() return valid pointers (see DCL30-C. Declare objects with appropriate storage durations).

Code Block
bgColor#FFCCCC
langc

int *p1,;
int *p2;
p1 = foo();
p2 = bar();

if (baz()) {
  return p1;
}
else {
  p2 = p1;
}
return p2;

Compliant Solution

This example can be corrected corrected in many different ways, depending on the intent of the programmer. In this compliant solution, p2 is found to be extraneous. The calls to bar() and baz() can be removed if they do not produce any side effects.

Code Block
bgColor#ccccff
langc

int *p1 = foo();

/* Removable if bar() does not produce any side effects */
(void)bar();

/* Removable if baz() does not produce any side effects */
(void)baz();
return p1;

Exceptions

Anchor
MSC13-EX1
MSC13-EX1
MSC13-EX1: Initializing a variable with a default value, such as 0, which gets subsequently overwritten may be inefficient, but is less of a problem than reading an uninitialized value, as per EXP33-C. Do not read uninitialized memory.

Risk Assessment

Unused values may indicate significant logic errors.

Recommendation

Severity

Likelihood

Remediation Cost

Priority

Level

MSC13-C

low

Low

unlikely

Unlikely

medium

Medium

P2

L3

Automated Detection

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

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Tool

Version

Checker

Description

Astrée
Include Page
Astrée_V
Astrée_V

Supported, but no explicit checker
CodeSonar
Include Page
CodeSonar_V
CodeSonar_V

LANG.STRUCT.UUVAL

Unused value

Coverity

Include Page
Coverity_V
Coverity_V

UNUSED_VALUE

Finds variables that are assigned pointer values returned from a function call but never used

Helix QAC

Include Page
Helix QAC_V
Helix QAC_V

C1500, C1502, C3203, C3205, C3206, C3207, C3229

DF2980, DF2981, DF2982, DF2983, DF2984, DF2985, DF2986


Klocwork
Include Page
Klocwork_V
Klocwork_V

LV_UNUSED.GEN
VA_UNUSED.GEN
VA_UNUSED.INIT


LDRA tool suite
Include Page
LDRA_V
LDRA_V

1 D, 8 D, 105 D, 94 D, 15 D

Fully implemented

Parasoft C/C++test
Include Page
Parasoft_V
Parasoft_V

CERT_C-MSC13-a

Avoid unnecessary local variables
PC-lint Plus

Include Page
PC-lint Plus_V
PC-lint Plus_V

438, 505, 529, 715, 838

Partially supported

Polyspace Bug Finder

Include Page
Polyspace Bug Finder_V
Polyspace Bug Finder_V

CERT C: Rec.

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MSC13-C


Checks for:

  • Unused parameter
  • Write without a further read

Rec. partially covered.

PVS-Studio

Include Page
PVS-Studio_V
PVS-Studio_V

V519, V596, V603, V714, V744, V751, V763, V1001, V5003
SonarQube C/C++ Plugin
Include Page
SonarQube C/C++ Plugin_V
SonarQube C/C++ Plugin_V
S1854

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Related Vulnerabilities

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

Other Languages

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Related Guidelines

SEI CERT C++

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Coding Standard

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VOID MSC13-CPP. Detect and remove unused values

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ISO/IEC TR 24772Likely Incorrect Expressions [KOA]
Dead and Deactivated Code [XYQ]
Unused Variable [XYR]

Bibliography

[Coverity 2007]


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Image Added Image Added PDTR 24772|AA. Bibliography#ISO/IEC PDTR 24772]\] "BRS Leveraging human experience," "KOA Likely incorrect expressions," "XYQ Dead and Deactivated Code," and "XYR Unused Variable"MSC12-C. Detect and remove code that has no effect      49. Miscellaneous (MSC)      Image Modified