In a .NET application, how can you configure trace switches in the application config file so that tracing can be controlled without recompiling code?

Introduction / Context:
Tracing is an important technique in .NET applications for diagnosing behaviour in different environments such as development, testing, and production. Trace switches allow you to control how much tracing information is produced without changing and recompiling the code. Understanding how to configure trace switches in the application configuration file is a common interview topic for developers and support engineers who maintain enterprise applications.

Given Data / Assumptions:

• We are working with a .NET application that uses System.Diagnostics tracing.
• We want to enable or disable trace output and control its level through configuration.
• The question focuses on configuring trace switches in the .config file.

Concept / Approach:
The System.Diagnostics namespace provides switch classes such as TraceSwitch and BooleanSwitch. These switches can be configured from app.config or web.config using the system.diagnostics configuration section. By defining switches with names and levels in the configuration file, you can change tracing behaviour at deployment time by editing configuration, without touching the compiled assemblies. The code reads the switch values at runtime and adapts its logging accordingly.

Step-by-Step Solution:
Step 1: In the configuration file, add a system.diagnostics section if it is not already present. Step 2: Under system.diagnostics, define a switches or sources block, and then create entries for each TraceSwitch or BooleanSwitch, specifying the name and value or level. Step 3: In your C# code, declare a static TraceSwitch field, for example static TraceSwitch generalSwitch = new TraceSwitch("General", "General trace switch"); Step 4: When your application runs, the switch reads its configuration from the .config file based on the name you provided, and its Level property reflects the configured setting. Step 5: Wrap trace statements in conditionals that check the switch level, for example if (generalSwitch.TraceInfo) Trace.TraceInformation("Some detail"); so output depends on configuration, not recompilation.

Verification / Alternative check:
To verify the setup, you can deploy the application with one set of switch values, observe the amount of trace output, then change the configuration file and restart the application. The trace behaviour should change without any need to rebuild or redeploy binaries. Official documentation and examples show this pattern of using system.diagnostics with switches, confirming that this is the intended approach for configurable tracing.

Why Other Options Are Wrong:
Option B is wrong because hard coding trace levels in source code makes it impossible to adjust logging behaviour without recompilation and redeployment. Option C is incorrect because simply creating a Windows service does not give fine grained, configurable tracing; the core mechanism is still System.Diagnostics with configuration. Option D is wrong because changing the project output type has no relation to trace switch configuration.

Common Pitfalls:
A common pitfall is misnaming the switch in configuration or in code, which causes the switch to use default values instead of the intended ones. Another issue is forgetting to deploy the .config file alongside the executable or web application, leading to unexpected trace behaviour. Some teams also overuse tracing at very verbose levels in production, which can impact performance and log storage. Using trace switches correctly helps you balance visibility and overhead by adjusting levels per environment.

Final Answer:
To configure trace switches, you define them under the system.diagnostics section in app.config or web.config and then read those settings through TraceSwitch or BooleanSwitch classes in code so that trace levels can be changed without recompiling.