68 lines
2.6 KiB
ReStructuredText
68 lines
2.6 KiB
ReStructuredText
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.. title:: clang-tidy - bugprone-inc-dec-in-conditions
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bugprone-inc-dec-in-conditions
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==============================
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Detects when a variable is both incremented/decremented and referenced inside a
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complex condition and suggests moving them outside to avoid ambiguity in the
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variable's value.
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When a variable is modified and also used in a complex condition, it can lead to
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unexpected behavior. The side-effect of changing the variable's value within the
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condition can make the code difficult to reason about. Additionally, the
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developer's intended timing for the modification of the variable may not be
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clear, leading to misunderstandings and errors. This can be particularly
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problematic when the condition involves logical operators like ``&&`` and
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``||``, where the order of evaluation can further complicate the situation.
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Consider the following example:
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.. code-block:: c++
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int i = 0;
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// ...
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if (i++ < 5 && i > 0) {
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// do something
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}
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In this example, the result of the expression may not be what the developer
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intended. The original intention of the developer could be to increment ``i``
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after the entire condition is evaluated, but in reality, i will be incremented
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before ``i > 0`` is executed. This can lead to unexpected behavior and bugs in
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the code. To fix this issue, the developer should separate the increment
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operation from the condition and perform it separately. For example, they can
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increment ``i`` in a separate statement before or after the condition is
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evaluated. This ensures that the value of ``i`` is predictable and consistent
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throughout the code.
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.. code-block:: c++
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int i = 0;
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// ...
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i++;
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if (i <= 5 && i > 0) {
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// do something
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}
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Another common issue occurs when multiple increments or decrements are performed
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on the same variable inside a complex condition. For example:
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.. code-block:: c++
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int i = 4;
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// ...
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if (i++ < 5 || --i > 2) {
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// do something
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}
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There is a potential issue with this code due to the order of evaluation in C++.
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The ``||`` operator used in the condition statement guarantees that if the first
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operand evaluates to ``true``, the second operand will not be evaluated. This
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means that if ``i`` were initially ``4``, the first operand ``i < 5`` would
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evaluate to ``true`` and the second operand ``i > 2`` would not be evaluated.
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As a result, the decrement operation ``--i`` would not be executed and ``i``
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would hold value ``5``, which may not be the intended behavior for the developer.
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To avoid this potential issue, the both increment and decrement operation on
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``i`` should be moved outside the condition statement.
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