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EXP30-C. Do not depend on the order of evaluation for side effects

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由 Robert C. Seacord创建, 最终由 David Svoboda修改于 十二月 02, 2020

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Evaluation of an expression may produce side effects. At specific points during execution, known as sequence points, all side effects of previous evaluations are complete, and no side effects of subsequent evaluations have yet taken place. Do not depend on the order of evaluation for side effects unless there is an intervening sequence point.

The C Standard, 6.5, paragraph 2 [ISO/IEC 9899:2011], states

If a side effect on a scalar object is unsequenced relative to either a different side effect on the same scalar object or a value computation using the value of the same scalar object, the behavior is undefined. If there are multiple allowable orderings of the subexpressions of an expression, the behavior is undefined if such an unsequenced side effect occurs in any of the orderings.

This requirement must be met for each allowable ordering of the subexpressions of a full expression; otherwise, the behavior is undefined. (See undefined behavior 35.)

https://wiki.sei.cmu.edu/confluence/display/c/EXP30-C.+Do+not+depend+on+the+order+of+evaluation+for+side+effects