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V1071. Consider inspecting the 'foo' fu…
Analyzer Diagnostics
General Analysis (C++)
General Analysis (C#)
General Analysis (Java)
Diagnosis of micro-optimizations (C++)
Diagnosis of 64-bit errors (Viva64, C++)
MISRA errors
AUTOSAR errors
Additional information
Contents

V1071. Consider inspecting the 'foo' function. The return value is not always used.

Apr 09 2021

The analyzer found that the return value of a function is ignored. In most cases, the result of the function is used in some way.

The diagnostic is designed to help in cases where a function or its return type is not marked with the standard attribute '[[nodiscard]]' (C23/C++17) or its analogs. If in most cases the result of the function was used in some way, and in certain situations, it is ignored, then this may indicate a possible error.

Consider a synthetic example:

int foo();
....
auto res = foo();
....
if (foo() == 42) { .... }
....
while (foo() != 42) { .... }
....
return foo();
....
foo();
....

Here, the result of the 'foo' function is used in four different ways, and then it is ignored in one. If the result is not used in less than 10% of the total number of calls, the analyzer will issue a warning.

In some situations, this code may have been written intentionally. For example, if the function contains some side effects - operations with a stream, reading/writing 'volatile' variables, etc., and the result can be ignored.

To help a programmer to understand that this behavior was intended, it is recommended to explicitly ignore the return value by casting it to the 'void' type:

....
(void) foo(); // or static_cast<void>(foo());
....

The analyzer does not issue warnings for the following cases:

  • constructors;
  • overloaded operators.
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