Add feature: Output human readable error codes

[dave992]

Originally added by @rtonnaer:

The Micro-Epsilon SDK outputs numerical error codes that are explained in the SDK Manual. The driver should output the error code with a text message containing the explanation in the SDK manual.

@gavanderhoorn I intend to make a translator function that translates a numerical value into a numerical value + text string. Is there a C++ structure (e.g. an error code function) that I should use.

---

Response by @gavanderhoorn :

These sort of things are typically done using either a map (which maps int to std::string), or even just a simple switch:

switch(error_code)
{
  ...

  case 302:
    return "Sensor is already connected";

  ...

  default:
    return "Unknown error code (please report)";
}

You could wrap this in a function which takes the error code and returns a std::string.

[dave992]

For the 0.2.0 version of the API (as used by this driver):
C++-Linux-InterfaceDocumentation.pdf

[rtonnaer]

@dave992 I created a feature branch and (very naively) just started to make a function in driver.cpp. The function is not a member of "scancontrol_driver::ScanControlDriver".

How to proceed, in general I want to:

1. define a function that returns a string does this work: std::string function_name(arg,arg1){ }
2. as a test: call this function directly as a first thing in the driver. As I want to test without sensor....

[dave992]

1. That prototype is nearly correct, the definition also needs the type of the input, in this case, an int or a derivative thereof, e.g:

std::string function_name(int error_code)
{
    std::string error_string;
    ....
    return error_string;
}

2. To test the function you do not need the driver, so calling your function at the beginning of main() should be okay for testing purposes. When it works you can move it to the correct place(s) in the driver code.

[gavanderhoorn]

1. To test the function you do not need the driver, so calling your function at the beginning of main() should be okay for testing purposes

suggestion: write an actual test and integrate it with the regular rostest framework.