The order of evaluation of subexpressions and the order in which side effects take place are frequently defined as unspecified behavior by the C Standard. Counterintuitively, unspecified behavior is where in behavior for whech the standard provides two or more possibilities and imposes no further requirements on which is chosen in any instance. Consequently, unspecified behavior can be a portability issue because different implementations can make different choices. If dynamic scheduling is used, however, there may not be a fixed-code execution sequence over the life of a process. Operations that can be executed in different sequences may in fact be executed in a different order.
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Following are specific examples of situations in which the order of evaluation of subexpressions or the order in which side effects take place is unspecified:
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This recommendation is related to EXP30-C. Do not depend on order of evaluation for side - effects, but it focuses on behavior that is nonportable or potentially confusing.
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A programmer could also violate the recommendation using dynamic memory passed to both functions, but that would be extremely difficult to detect using static analysis.
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
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