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V788. Review captured variable in lambd…
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

V788. Review captured variable in lambda expression.

May 23 2017

The analyzer detected a suspicious variable capture in a lambda function.

Consider a few examples of this diagnostic.

Example 1:

int x = 0;
auto f = [x] { };
....
x = 42;
f();
...

A variable whose exact value can be calculated at compile time is captured by value in a lambda function. Inside that function, the variable will be referring to the value that it had at the moment when it was captured rather than at the moment when the function call was executed. The variable should probably be captured by reference instead.

int x = 0;
auto f = [&x] { };
....
x = 42;
f();
...

Another possible explanation is that the code where the variable used to be assigned some value was removed during refactoring.

int x = 0;
if (condition) x = 42;
else x = 43;
auto f = [x] { };

If you need to capture a constant, a better solution would be to explicitly declare the variable's type as 'const' or 'constexpr'.

constexpr int x = 0;
auto f = [x] { };

Example 2:

int x;
auto f = [x] { };

An uninitialized variable is captured by value. Using it will lead to undefined behavior. If the variable was meant to be initialized by the function call, then it should be captured by reference.

int x;
auto f = [&x] { x = 42; };

This diagnostic is classified as:

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