How to build a node with yaml-cpp?

Question

I want to use yaml-cpp for a project of mine to generate a yaml-file however I have trouble figuring out how exactly I have to go about this. The yaml file I need to emit should look like this:

action_counts:
  version: 0.3
  subtree:
    - name: system
      local:
      - name: adder
        action_counts:
          - name: add
            counts: 1000
          - name: idle
            counts: 10000

So far I haven't been able to write the last four lines. I know that a '-' represents an array but I don't know how I can print the name and counts keys like that.

I have written some bits of code to experiment with yaml-cpp. The code looked like this:

    YAML::Node node;

    node["action_counts"] = YAML::Null;
    node["action_counts"]["version"] = "0.3";

    node["action_counts"]["subtree"].push_back("system");

    std::ofstream fout("fileUpdate.yaml"); 
    fout << node; 

    return 0;

And the output it produces is this:

action_counts:
  version: 0.3
  subtree:
    - system

The last line here is wrong but I haven't managed to find out how to print - name: system instead of this. How do I do this?

Once thats done how do I print the rest? Is local a part of the - name array? I think once I know how to format those to two lines I can figure out the rest by myself.

score 4 · Accepted Answer · answered Nov 17 '20 at 12:39

Lots of examples of creating messages can be found in the tests of yaml-cpp library.

The desired structure can be formed as follows:

#include <fstream>
#include "yaml-cpp/yaml.h"

int main() {
    YAML::Node action_1;
    action_1["name"] = "add";
    action_1["counts"] = 1000;

    YAML::Node action_2;
    action_2["name"] = "idle";
    action_2["counts"] = 10000;

    YAML::Node local_item;
    local_item["name"] = "adder";
    local_item["action_counts"].push_back(action_1);
    local_item["action_counts"].push_back(action_2);

    YAML::Node local;
    local.push_back(local_item);

    YAML::Node subtree_item;
    subtree_item["name"] = "system";
    subtree_item["local"] = local;

    YAML::Node root;
    root["action_counts"]["version"] = "0.3";
    root["action_counts"]["subtree"].push_back(subtree_item);

    std::ofstream fout("fileUpdate.yaml");
    fout << root;

    return 0;
}

score 1 · Answer 2 · answered Nov 17 '20 at 10:53

The value in the array is just another mapping with the keys name and local, so you need to put that mapping into the array, e.g.:

YAML::Node systemTree;

systemTree["name"] = "system";
/* assuming you have put together adderTree similarly */
systemTree["local"].push_back(adderTree);

YAML::Node root;

root["action_counts"] = YAML::Null;
root["action_counts"]["version"] = "0.3";

root["action_counts"]["subtree"].push_back(systemTree);

How to build a node with yaml-cpp?

2 Answers2