Why Do C# Loops with Captured Variables Produce Unexpected Results?
Feb 03, 2025 am 08:20 AM
In C#, developers encounter an interesting problem when using capture variables in cycle iteration. Consider the following code fragment:
Although the expected output is 0, 2, 4, 6, and 8, the code unexpectedly output five 10. The reason for this behavior is the captured variables
List<Action> actions = new List<Action>();
int variable = 0;
while (variable < 5)
{
actions.Add(() => Console.WriteLine(variable * 2));
++variable;
}
foreach (var act in actions)
{
Console.WriteLine(act.Invoke());
}. All operations quote the same examples of <同>. When variables change in the cycle, this may lead to unpredictable results.
variable <決> Solve the problem of capture variables variable
In order to overcome this limit and allow each operation to have its own capture variables, C# provides a simple solution:
By creating a copy of thein the cycle, each operation captures its own sole examples, so as to ensure that
changes outside the lambda expression will not affect the capture value.while (variable < 5)
{
int copy = variable;
actions.Add(() => Console.WriteLine(copy * 2));
++variable;
}
<常> Other common situations variable variable
and iteration:
In these two cases, the local copy of the variable is required to capture the current cycle iteration. for
foreach <論> Conclusion
// For loop
for (int i = 0; i < 5; i++)
{
// ... similar issue ...
}
// Foreach loop
// ... similar issue ...
Understanding the behavior of capturing variables in the C# cycle is essential to avoid accidents. The solution discussed in this article ensures that each operation has its own independent capture variables, thereby achieving predictable and expected behaviors.
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