C/C++ library for non-intrusive user-friendly configuration

Question

I am looking for a C or C++ open-source library for exposing configuration-related variable via an API and a web UI. The requirements are:

R1. It should be non-intrusive for the programmer. Assume an existing code has a global variable const bool show_fps = false (i.e., a debugging relic), a programmer should be able to write something like:

bool show_fps = true;  // only "const" is removed
CONFIG(&show_fps,  // variable
    "debug.show_fps",  // API identifier
    "Show FPS",  // short user-friendly title
    "Enable/disable displaying the number of frames per second of the video pipeline",  // long user-friendly description
);

R2. It should expose an API (e.g., REST, line-oriented) which allows:

• to list configuration variables, their user-friendly title and their description;
• to determine their current value;
• to set the value of a variable.

R3. It should expose a single-page web UI which present the above API in a user-friendly manner.

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Since, I got the question previously: I know that C and C++ are not the same thing, however, I believe that writing an adapter from one language to another implies a lot less effort that writing a library fulfilling the above requirements from scratch. Hence, I am open to both C and C++ libraries.

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Below are some examples of libraries and frameworks I came across during my research and why they fall short:

• Boost program_options fits R1 quite nicely:

  int opt;
  po::options_description desc("Allowed options");
  desc.add_options()
      ("optimization", po::value<int>(&opt)->default_value(10), "optimization level")
  ;
  

  However, it seems to be geared towards the command-line, environment variables and configuration files, hence not fulfilling R2 and R3.

• I drew a lot of inspiration from the Linux kernel's moduleparam.h header:

  static int max_loop;
  module_param(max_loop, int, 0444);
  MODULE_PARM_DESC(max_loop, "Maximum number of loop devices");
  

  It fits requirement R1 quite well. R2 is almost fulfilled, i.e., said configuration can be manipulated via sysfs, however, an API that is not kernel-specific is required. R3 is not fulfilled.

• etcd is an excellent server-software for storing key-value configuration variables organized as a tree, partially fulfilling R2 and R3. However, it does not have a notion of user-friendly title and description for each variable. Furthermore, I found no library to integrate with it non-intrusively (R1).

Answer 1

I ended up writing my own library under a MIT license. If anybody ever has the same problem feel free to use it: https://github.com/cristiklein/cpprestconfig

Contributions welcome!