To register an operator, call v2_operator_create from init :

extern "C" V2_EXPORT void init( v2_context_t ctx )
{
  v2_operator_t op = v2_operator_create(
    ctx,             // the context passed by the engine to init
    "demo.strlen",   // operator ID; must be globally unique
    "Strlen Demo",   // user-friendly operator name
    init_strlen      // initialization handler (see below)
  );

  // Add an input port so the operator can receive and process data:
  v2_operator_add_input(
    op,         // pointer returned by v2_operator_create
    "inString", // port name; must be unique within this operator
    "string"    // port type
  );

  // Add an output port so the operator can send data:
  v2_operator_add_output( op, "outLength", "int64" );
}

The subengine does not impose any special format for port names, but we recommended prefixing them with in or out. The prefixing makes it easier to identify them apart when their names appear in the logs.

const char* init_strlen( v2_process_t proc )
{
  v2_process_set_port_handler(
    proc,             // the process, created by the engine
    "inString",       // which port this handler is associated with
    strlen_on_input   // the actual handler (below)
  );

  return NULL; // no error
}

const char* strlen_on_input( v2_process_t proc, v2_datum_t datum )
{
  // Extract the string contained in `datum`
  const char* str = v2_datum_get_string( datum );

  size_t len = strlen( str );

  // Create the output datum containing the length
  // of the input string
  v2_datum_t out = v2_datum_from_int64( (int64_t)len );
  // Write it to the output port
  v2_process_output( proc, "outLength", out );
  // Release the `out` handle (see explanation below)
  v2_datum_release( out );

  return NULL; // no error
}

Result

You have created a basic operator. The initialization and termination, configuration properties, and timed handlers (timers) are described in the subsequent chapters of this guide.

# Compile C/C++ sources into position-independent object files (.o)
$ gcc -c -fPIC <sources>
# Link the object files together into a shared object
$ gcc -shared -o <output-name>.so <object-files>