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+# Supplying main() yourself
+
+**Contents**<br>
+[Let Catch2 take full control of args and config](#let-catch2-take-full-control-of-args-and-config)<br>
+[Amending the Catch2 config](#amending-the-catch2-config)<br>
+[Adding your own command line options](#adding-your-own-command-line-options)<br>
+[Version detection](#version-detection)<br>
+
+The easiest way to use Catch2 is to use its own `main` function, and let
+it handle the command line arguments. This is done by linking against
+Catch2Main library, e.g. through the [CMake target](cmake-integration.md#cmake-targets),
+or pkg-config files.
+
+If you want to provide your own `main`, then you should link against
+the static library (target) only, without the main part. You will then
+have to write your own `main` and call into Catch2 test runner manually.
+
+Below are some basic recipes on what you can do supplying your own main.
+
+
+## Let Catch2 take full control of args and config
+
+This is useful if you just need to have code that executes before/after
+Catch2 runs tests.
+
+```cpp
+#include <catch2/catch_session.hpp>
+
+int main( int argc, char* argv[] ) {
+  // your setup ...
+
+  int result = Catch::Session().run( argc, argv );
+
+  // your clean-up...
+
+  return result;
+}
+```
+
+_Note that if you only want to run some set up before tests are run, it
+might be simpler to use [event listeners](event-listeners.md#top) instead._
+
+
+## Amending the Catch2 config
+
+If you want Catch2 to process command line arguments, but also want to
+programmatically change the resulting configuration of Catch2 run,
+you can do it in two ways:
+
+```c++
+int main( int argc, char* argv[] ) {
+  Catch::Session session; // There must be exactly one instance
+
+  // writing to session.configData() here sets defaults
+  // this is the preferred way to set them
+
+  int returnCode = session.applyCommandLine( argc, argv );
+  if( returnCode != 0 ) // Indicates a command line error
+        return returnCode;
+
+  // writing to session.configData() or session.Config() here
+  // overrides command line args
+  // only do this if you know you need to
+
+  int numFailed = session.run();
+
+  // numFailed is clamped to 255 as some unices only use the lower 8 bits.
+  // This clamping has already been applied, so just return it here
+  // You can also do any post run clean-up here
+  return numFailed;
+}
+```
+
+If you want full control of the configuration, don't call `applyCommandLine`.
+
+
+## Adding your own command line options
+
+You can add new command line options to Catch2, by composing the premade
+CLI parser (called Clara), and add your own options.
+
+```cpp
+int main( int argc, char* argv[] ) {
+  Catch::Session session; // There must be exactly one instance
+
+  int height = 0; // Some user variable you want to be able to set
+
+  // Build a new parser on top of Catch2's
+  using namespace Catch::Clara;
+  auto cli
+    = session.cli()           // Get Catch2's command line parser
+    | Opt( height, "height" ) // bind variable to a new option, with a hint string
+        ["-g"]["--height"]    // the option names it will respond to
+        ("how high?");        // description string for the help output
+
+  // Now pass the new composite back to Catch2 so it uses that
+  session.cli( cli );
+
+  // Let Catch2 (using Clara) parse the command line
+  int returnCode = session.applyCommandLine( argc, argv );
+  if( returnCode != 0 ) // Indicates a command line error
+      return returnCode;
+
+  // if set on the command line then 'height' is now set at this point
+  if( height > 0 )
+      std::cout << "height: " << height << std::endl;
+
+  return session.run();
+}
+```
+
+See the [Clara documentation](https://github.com/catchorg/Clara/blob/master/README.md)
+for more details on how to use the Clara parser.
+
+
+## Version detection
+
+Catch2 provides a triplet of macros providing the header's version,
+
+* `CATCH_VERSION_MAJOR`
+* `CATCH_VERSION_MINOR`
+* `CATCH_VERSION_PATCH`
+
+these macros expand into a single number, that corresponds to the appropriate
+part of the version. As an example, given single header version v2.3.4,
+the macros would expand into `2`, `3`, and `4` respectively.
+
+
+---
+
+[Home](Readme.md#top)