catch2/docs/own-main.md

Supplying main() yourself

The easiest way to use Catch is to let it supply main() for you and handle configuring itself from the command line.

This is achieved by writing #define CATCH_CONFIG_MAIN before the #include "catch.hpp" in exactly one source file.

Sometimes, though, you need to write your own version of main(). You can do this by writing #define CATCH_CONFIG_RUNNER instead. Now you are free to write main() as normal and call into Catch yourself manually.

You now have a lot of flexibility - but here are three recipes to get your started:

Let Catch take full control of args and config

If you just need to have code that executes before and/ or after Catch this is the simplest option.

#define CATCH_CONFIG_RUNNER
#include "catch.hpp"

int main( int argc, char* argv[] ) {
  // global setup...

  int result = Catch::Session().run( argc, argv );

  // global clean-up...

  return result;
}

Amending the config

If you still want Catch to process the command line, but you want to programatically tweak the config, you can do so in one of two ways:

#define CATCH_CONFIG_RUNNER
#include "catch.hpp"

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;
}

Take a look at the definitions of Config and ConfigData to see what you can do with them.

To take full control of the config simply omit the call to applyCommandLine().

Adding your own command line options

Catch embeds a powerful command line parser called Clara. As of Catch2 (and Clara 1.0) Clara allows you to write composable option and argument parsers, so extending Catch's own command line options is now easy.

#define CATCH_CONFIG_RUNNER
#include "catch.hpp"

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 Catch's
  auto cli 
    = session.cli() // Get Catch's composite 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 Catch so it uses that
  session.cli( cli ); 
  
  // Let Catch (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 for more details.

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