SEI CERT C Coding Standard

Space shortcuts

Page tree

Versions Compared

Old Version 31

changes.mady.by.user David Svoboda

Saved on

compared with

New Version 32

changes.mady.by.user Melanie Thompson

Saved on

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.

...

According to C99, Section 6.5, "Expressions":

Except as specified later (for the function-call (), &&, ||, ?:, and comma operators), the order of evaluation of subexpressions and the order in which side effects take place are both unspecified.

...

This recommendation is related to guideline EXP30-C. Do not depend on order of evaluation between sequence points, but focuses on behavior that is nonportable or potentially confusing.

...

The order of evaluation of the function designator, the actual arguments, and subexpressions within the actual arguments is are unspecified, but there is a sequence point before the actual call.

...

Recommendation

Severity

Likelihood

Remediation Cost

Priority

Level

EXP10-C

medium

probable

medium

P8

L2

Automated Detection

Tool

Version

Checker

Description

Section

Compass/ROSE

 

 

Section

could detect violations of this recommendation by searching for the following pattern:

  • Any expression that calls two functions between the same sequence points
  • Those two functions both modify the value of a static variable
  • That static variable's value is referenced by code following the expression
Section

...

Coverity Prevent

Include Page
c:Coverity_V
c:Coverity_V
Section

EVALUATION_ORDER

...

Section

can detect the specific instance where Statement contains multiple side-effects on the same value with an undefined evaluation order because with different compiler flags or different compilers or platforms, the statement may behave differently.

One could also violate the recommendation using dynamic memory passed to both functions, but that would be extremely difficult to detect using static analysis.

...

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 : EXP10-CPP. Do not depend on the order of evaluation of subexpressions or the order in which side effects take place.

Bibliography

Wiki Markup
\[[ISO/IEC 9899:1999|AA. Bibliography#ISO/IEC 9899-1999]\] Section 6.5, "Expressions," Section 6.5.16, "Assignment operators," Section 6.5.2.2, "Function calls," and Section 6.7.8, "Initialization"
\[[ISO/IEC PDTR 24772|AA. Bibliography#ISO/IEC PDTR 24772]\] "JCW Operator precedence/Order of Evaluation" and "SAM Side-effects and Order of Evaluation"
\[[MISRA 042004|AA. Bibliography#MISRA 04]\] Rule 12.2

...