How to parse txt file from middle to particular string using C++?

Question

I have to parse a TXT file of XML messages and save the ID value in another file. I can reach up to the <ID> tag using find function. But how to get the value, also the length of value varies.

<note>
    <to>Tove</to>
    <from>Jani</from>
    <ID>Fx12345</ID>
    <body>Don't forget me this weekend!</body>
</note>
<note>
    <to>Tove</to>
    <from>Alex</from>
    <ID>Fx1236785</ID>
    <body>Don't forget me this weekend!</body>
</note>

I'm using this approach

while (!fileInput.eof()) {
   getline(fileInput, line);
    if ((offset = line.find("<ID>", 0)) != string::npos) {
        // How to get only value
    }
}

I'd suggest using a proper XML parsing library rather than rolling your own fragile parser. — cdhowie, Aug 22 '14 at 19:09
I would like to add a link to [this SO answer](http://stackoverflow.com/a/9387612/2700399) to what @cdhowie already said. — Bart van Nierop, Aug 22 '14 at 19:15
I would appreciate if anyone can share the logic atleast it will improve my concepts — Abhi, Aug 22 '14 at 19:16
_@Abhi _"atleast it will improve my concepts"_ Your _concept_ is very likely to fail parsing XML text properly. You should stick with @cdhowie's advice. — πάντα ῥεῖ, Aug 22 '14 at 19:23
Most, if not all of the libraries in the answer I've linked are open source. Study their code to improve your concepts. — Bart van Nierop, Aug 22 '14 at 19:23

score 4 · Accepted Answer · answered Aug 22 '14 at 19:16

string::find() has an overload that specifies the position to start the search. So simply start a second search, starting at the end of <ID>, to look for </ID>. You are after what comes in between the two. Pretty simple really.

However, as suggested elsewhere, there are a lot of XML parsers out there. Using a full XML parser would be recommended if the input file could have some variations.

How to parse txt file from middle to particular string using C++?

1 Answers1