Re: Parsing YAML into key:value tree nodes with C library
"Felix Krause" <[email protected]> Mon, 16 Aug 2021 21:01:02 +0200
| Newsgroups | gmane.text.yaml.general |
|---|---|
| Message-ID | <[email protected]> |
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Hi David,
libyaml does contain such an API:
https://github.com/yaml/libyaml/blob/master/include/yaml.h#L1457
This gives you a `yaml_document_t` with a root node accessible via
`yaml_document_get_root_node`. The API is not well-documented but
basically nodes can refer to sub-nodes via an `int` index and you use
`yaml_document_get_node` to retrieve subnodes.
mapping and sequence nodes store their children in a stack structure –
you iterate them via
```
for (yaml_node_item_t *cur = node->data.sequence.start; cur !=
node->data.sequence.top; ++cur) {
// ...
}
```
Now if you load in a YAML that contains a mapping with scalar key/value
pairs, your root node will be a mapping and the subnodes will be
scalars.
---
If you want a more convenient API, I did write this utility in the past:
https://github.com/flyx/libyaml_constructor
It is a code generator that reads in a C header containing type
definitions and autogenerates code that loads YAML into those types
(using libyaml). With this, you can define how your YAML structure must
look via C types and some annotations in the given header.
That tool was a part of a project which I abandoned, hence I never did a
proper release. However it did work quite well for all I can remember.
The compile-time dependency on libclang (to parse your C header) may be
a bit of a hurdle.
Cheers,
Felix
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<meta http-equiv=3D"Content-Type" content=3D"text/xhtml; charset=3Dutf-8"=
>
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<body>
<div style=3D"font-family:sans-serif"><div style=3D"white-space:normal">
<p dir=3D"auto">Hi David,</p>
<p dir=3D"auto">libyaml does contain such an API: <a href=3D"https://gith=
ub.com/yaml/libyaml/blob/master/include/yaml.h#L1457" style=3D"color:#398=
3C4">https://github.com/yaml/libyaml/blob/master/include/yaml.h#L1457</a>=
</p>
<p dir=3D"auto">This gives you a <code style=3D"background-color:#F7F7F7;=
border-radius:3px; margin:0; padding:0 0.4em" bgcolor=3D"#F7F7F7">yaml_d=
ocument_t</code> with a root node accessible via <code style=3D"backgroun=
d-color:#F7F7F7; border-radius:3px; margin:0; padding:0 0.4em" bgcolor=3D=
"#F7F7F7">yaml_document_get_root_node</code>. The API is not well-documen=
ted but basically nodes can refer to sub-nodes via an <code style=3D"back=
ground-color:#F7F7F7; border-radius:3px; margin:0; padding:0 0.4em" bgcol=
or=3D"#F7F7F7">int</code> index and you use <code style=3D"background-col=
or:#F7F7F7; border-radius:3px; margin:0; padding:0 0.4em" bgcolor=3D"#F7F=
7F7">yaml_document_get_node</code> to retrieve subnodes.</p>
<p dir=3D"auto">mapping and sequence nodes store their children in a stac=
k structure =E2=80=93 you iterate them via</p>
<pre style=3D"background-color:#F7F7F7; border-radius:5px 5px 5px 5px; ma=
rgin-left:15px; margin-right:15px; max-width:90vw; overflow-x:auto; paddi=
ng:5px" bgcolor=3D"#F7F7F7"><code style=3D"background-color:#F7F7F7; bord=
er-radius:3px; margin:0; padding:0" bgcolor=3D"#F7F7F7">for (yaml_node_it=
em_t *cur =3D node->data.sequence.start; cur !=3D node->data.sequen=
ce.top; ++cur) {
// ...
}
</code></pre>
<p dir=3D"auto">Now if you load in a YAML that contains a mapping with sc=
alar key/value pairs, your root node will be a mapping and the subnodes w=
ill be scalars.</p>
<hr style=3D"background:#333; background-image:linear-gradient(to right, =
#ccc, #333, #ccc); border:0; height:1px" height=3D"1">
<p dir=3D"auto">If you want a more convenient API, I did write this utili=
ty in the past: <a href=3D"https://github.com/flyx/libyaml_constructor" s=
tyle=3D"color:#3983C4">https://github.com/flyx/libyaml_constructor</a></p=
>
<p dir=3D"auto">It is a code generator that reads in a C header containin=
g type definitions and autogenerates code that loads YAML into those type=
s (using libyaml). With this, you can define how your YAML structure must=
look via C types and some annotations in the given header.</p>
<p dir=3D"auto">That tool was a part of a project which I abandoned, henc=
e I never did a proper release. However it did work quite well for all I =
can remember. The compile-time dependency on libclang (to parse your C he=
ader) may be a bit of a hurdle.</p>
<p dir=3D"auto">Cheers,<br>
Felix</p>
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