Accessing fields by name

[jslezosky]

Using the following yaml in file "test.yaml":

commands:
    IAU_BOOT_RST:
        - dmoab_scid: {value: 1, type: uint8_t, size: 4}
        - dmoab_opcode: {value: 2, type: uint8_t, size: 4}
        - dmoab_extension: {value: 3, type: uint8_t, size: 8}
        - dmoab_operand: {value: [0,0,0,0,17], type: vector<uint8_t>, size: 40}
        - dmoab_crc: {value: 0, type: uint8_t, size: 8}
    IAU_WD_EN:
        - dmoab_scid: {value: 4, type: uint8_t, size: 4}
        - dmoab_opcode: {value: 5, type: uint8_t, size: 4}
        - dmoab_extension: {value: 6, type: uint8_t, size: 8}
        - dmoab_operand: {value: [0,0,0,0,34], type: vector<uint8_t>, size: 40}
        - dmoab_crc: {value: 0, type: uint8_t, size: 8}

I want to access the integer value of dmoab_extension, size for each command.
I thought I could access the fields by name using the following code:

std::string contents = file_get_contents<std::string>("test.yaml");
ryml::Tree tree = ryml::parse_in_arena(ryml::to_csubstr(contents)); 

ryml::NodeRef root = tree["commands"];

// iterate children
for (ryml::NodeRef const& command : root.children())
{
    std::cout << "size " << command["IAU_BOOT_RST"]["dmoab_extension"]["size"].val() << std::endl
}

Of course this code crashes.
What is the correct method for accessing children by name?
Once I do access "size", how do I read it as an integer or uint8_t?

[biojppm]

Your loop variable is already the command, so you are looking twice for IAU_BOOT_RST. That is, you are doing the equivalent to tree["commands"]["IAU_BOOT_RST"]["IAU_BOOT_RST"]["dmoab_extension"]["size"], and it fails.

What you want is simply this:

for (ryml::NodeRef const& cmd : tree["commands"].children())
  std::cout << cmd.key() << ": size=" << cmd["dmoab_extension"]["size"].val() << "\n";

As for the conversion, it's in the quickstart. In this case:

int size;
cmd["dmoab_extension"]["size"] >> size;

[jslezosky]

I really appreciate you working with me on this.
I know this should work, but it crashes.
On the command line I get:

C:\EASY\rapidyaml\src_singleheader\ryml_all.hpp:24170:check failed: (is_map(node))

From the debugger, it is crashing at:
size_t Tree::find_child(size_t node, csubstr const& name) const
{
_RYML_CB_ASSERT(m_callbacks, node != NONE);
_RYML_CB_ASSERT(m_callbacks, is_map(node));

With node = 2, name = "dmoab_extension"

I must have something fundamentally wrong, but I can't figure it out.

[jslezosky]

I tried the following code:

for (ryml::NodeRef const& cmd : tree["commands"].children())
{
    std::cout << cmd.key() << ": size=" << cmd[0]["dmoab_scid"]["size"].val() << "\n";
    std::cout << cmd.key() << ": size=" << cmd[0]["dmoab_extension"]["size"].val() << "\n";
}

the dmoab_scid line prints : IAU_BOOT_RST: size=4
but the dmoab_extension line crashes.

[biojppm]

I overlooked that each command is a sequence and not a map. So to get at the scid/extension nodes you'll have to provide the proper sequence index:

for (ryml::NodeRef const& cmd : tree["commands"].children())
{
    // _scid is at position 0
    std::cout << cmd.key() << ": size=" << cmd[0]["dmoab_scid"]["size"].val() << "\n";
    // NOTE _extension is at position 2
    std::cout << cmd.key() << ": size=" << cmd[2]["dmoab_extension"]["size"].val() << "\n";
}

The solution is in realizing that dmoab_extension is the single child of cmd[2] and not cmd[0].

The assert is firing because when you write cmd[0]["dmoab_extension"], the cmd[0] part is going to return the first child node of cmd which is a map with a single keyval dmoab_scid: {..., size: 4}. Then cmd[0]["dmoab_extension"] does not exist, so it returns a seed node (ie, is typeless and can be written but not read), so calling cmd[0]["dmoab_extension"]["size"] fails because cmd[0]["dmoab_extension"] is typeless and not a map.

BTW, why use a sequence structure for the command? Why not a map directly, like this?

commands:
  IAU_BOOT_RST:
    # notice it is not this:
    #- dmoab_scid: {value: 1, type: uint8_t, size: 4}
    dmoab_scid: {value: 1, type: uint8_t, size: 4}
    dmoab_opcode: {value: 2, type: uint8_t, size: 4}
    dmoab_extension: {value: 3, type: uint8_t, size: 8}
    dmoab_operand: {value: [0,0,0,0,17], type: vector<uint8_t>, size: 40}
    dmoab_crc: {value: 0, type: uint8_t, size: 8}
  IAU_WD_EN:
    dmoab_scid: {value: 4, type: uint8_t, size: 4}
    dmoab_opcode: {value: 5, type: uint8_t, size: 4}
    dmoab_extension: {value: 6, type: uint8_t, size: 8}
    dmoab_operand: {value: [0,0,0,0,34], type: vector<uint8_t>, size: 40}
    dmoab_crc: {value: 0, type: uint8_t, size: 8}

With the above structure you would not need cmd[0]["dmoab_scid"] and cmd[2]["dmoab_extension"], just cmd["dmoab_scid"] and cmd["dmoab_extension"], as would generally be expected.

[jslezosky]

Thank you! This helps me iterate over my commands.
I am completely new to YAML, so I'm learning the difference between sequences and maps.
I converted the commands to maps and, just as you said, I can access the fields by name, without having to use the [0] index.
There are other consumers of this file, so I'd have to get their approval before switching all commands to maps.