commandIO: a CLI and REPL interface generator for C++

This library provides a simple way to expose any C/C++ function in a Read-eval-print loop (REPL) interactive environment.


  • Easy interface definition.
  • Interface support for: - Positional parameters. - Optional parameters with default values. - Flags.
  • Class methods.
  • Automatic parameter- and return type inference.
  • Full help system.
  • Method discovery.



We show how to use simple functions in the demo program. In this program we export three functions: greet, inc and mul.

The built in help function shows a list of available commands.

> help
Available commands:
  greet         Say hi to someone.
  inc           Increment a value.
  mul           Multiply a floating point number.
  help          Help on a specific command.
  exit          Exit.

For more information about a specific command, pass the name of a command to the help function.

> help greet
greet: Say hi to someone.

positional arguments:
  name          someone's name (type string)

optional arguments:
  -t            greet multiple times (type int, default: 1)
  -s            shout (type flag)


This particular command has one positional (mandatory) parameter and two optional parameters, of which one is a flag.

From the description, we see that we can call the greet function by providing only one argument as follows.

> greet world
Hi world.

Stings consisting of multiple words should be quoted.

> greet "Dan the man"
Hi Dan the man.

We can override the default value of the optional parameter by adding the -t option.

> greet -t 3 world
Hi world.
Hi world.
Hi world.

Flags do not take an additional argument.

> greet -t 3 -s world
HI world!
HI world!
HI world!

Optional arguments can be provided in any order.

> greet -s world -t 3
HI world!
HI world!
HI world!


In the calculator program we show how to use class methods. In this program we export some simple arithmetic functions.

> help
name (return type: parameter types) ; documentation

add (void: int) ; Add something.
sub (void: int) ; Subtract something.
show (int:) ; Show result.
help (string:) ; This help message.
exit (void:) ; Exit.

These functions operate on an object.

$ ./calculator
> show
> add 10
> sub 2
> show
> exit