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The presence of unused values may indicate significant logic errors. To prevent such errors, unused values should be identified and removed from code.

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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

Wiki MarkupIn 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 in compliance with \[[DCL30-C|DCL30-C. Do not refer to an object outside of its lifetime]\]pointers (see DCL30-C. Declare objects with appropriate storage durations).

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 initialized to NULL rather than the result of bar()found to be extraneous. The calls to bar() and baz() can be removed if they do not produce any side effects.

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

p2/* =Removable NULL;

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

Risk Assessment

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

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

Exceptions

Risk Assessment

Unused The presence of unused values may indicate significant logic errors.

Automated Detection

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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.

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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. 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

Related Vulnerabilities

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

References

*Coverity 07 Section 6.1.20, "UNUSED_VALUE"

Related Guidelines

Bibliography

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Image Added Image Added Image AddedReferences
Coverity 07 Coverity Prevent? User's Manual (3.3.0) (2007).