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Potentially dangerous use of non-short-circuit logic

ID: cs/non-short-circuit Kind: problem Security severity: Severity: error Precision: high Tags: - quality - reliability - correctness - external/cwe/cwe-480 - external/cwe/cwe-691 Query suites: - csharp-code-quality.qls - csharp-security-and-quality.qls

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The | and & logical operators, known as non-short circuit operators, should not be used. Using a non-short circuit operator reduces the efficiency of the program, is potentially confusing and can even lead to the program crashing if the first operand acts as a safety check for the second.

Recommendation

If the non-short circuit operator is unintended then replace the operator with the short circuit equivalent. Sometime a non-short circuit operator is required because the operands have side effects. In this case it is more efficient to evaluate both operands separately and then use a short circuit operator to combine the results.

Example

This example will crash because both parts of the conditional expression will be evaluated even if a is null.

class DangerousNonShortCircuitLogic { public static void Main(string[] args) { string a = null; if (a != null & a.ToLower() == "hello world") { Console.WriteLine("The string said hello world."); } } }

The example is easily fixed by using the short circuit AND operator. The program produces no output but does not crash, unlike the previous example.

class DangerousNonShortCircuitLogicFix { public static void Main(string[] args) { string a = null; if (a != null && a.ToLower() == "hello world") { Console.WriteLine("The string said hello world."); } } }

References