Implement mssql outer apply functionality for parsing xml - c++

Question

I want to implement the mssql outer apply functionality for parsing xml in an imperative language (c/c++, vba, java etc.), in principle any, the algorithm itself is interesting.
For example, I have a such xml:
<?xml version="1.0" encoding="utf-8"?>
<main>
<fio n="attr">
<name>name1</name>
<pasp>
<pi>pi1</pi>
<pi>pi2</pi>
</pasp>
</fio>
<fio n="attr">
<name>name2</name>
</fio>
<sub_node>
<cr>
<val>val1</val>
<val>val2</val>
<extra>
<ex>ex1</ex>
<ex>ex2</ex>
</extra>
</cr>
<cr>
<val>val3</val>
<val>val4</val>
</cr>
</sub_node>
</main>
On mssql I can parse it like this:
declare #sCmd nvarchar(max), #sFullPath varchar(max), #x xml
set #sFullPath = 'c:\in\test2.xml'
set #sCmd = N'select #xml = cast(t.data as xml) from OPENROWSET (BULK '+quotename(#sFullPath, N'''') + N', SINGLE_BLOB) t(data)'
exec sp_executesql #sCmd, N'#xml xml output', #x output;
select distinct
fio.n.value('name[1]', 'varchar(32)') 'fio.name'
, pi_.n.value('.', 'varchar(32)') 'pi_'
, val.n.value('.', 'varchar(5)') 'val'
, ex.n.value('.', 'varchar(10)') 'ex'
from #x.nodes('main') as main(n)
outer apply main.n.nodes('fio[#n="attr"]') as fio(n)
outer apply fio.n.nodes('pasp/pi') as pi_(n)
outer apply main.n.nodes('sub_node/cr') as cr(n)
outer apply cr.n.nodes('val') as val(n)
outer apply cr.n.nodes('extra/ex') as ex(n)
And I get the following result:
name1 pi1 val1 ex1
name1 pi1 val1 ex2
name1 pi1 val2 ex1
name1 pi1 val2 ex2
name1 pi1 val3 NULL
name1 pi1 val4 NULL
name1 pi2 val1 ex1
name1 pi2 val1 ex2
name1 pi2 val2 ex1
name1 pi2 val2 ex2
name1 pi2 val3 NULL
name1 pi2 val4 NULL
name2 NULL val1 ex1
name2 NULL val1 ex2
name2 NULL val2 ex1
name2 NULL val2 ex2
name2 NULL val3 NULL
name2 NULL val4 NULL
Tell me please how this can be implemented in an any imperative language using, for example, only loops, recursion, SelectNodes(), SelectSingleNode(), etc. Despite the fact that this is only an exemplary xml, for example, tags may be missing in some other file, and nested loops just don’t work correctly... And the xpath strings can be different, how to make a universal algorithm?