Read a line from xml file using C++

Question

My XML File has:

< Package > xmlMetadata < /Package >

I am searching for a tag in this file and the text between the startin

Answer 1

A single line of tags on a file can hardly be described as XML. Anyway, if you really want to parse a XML file, this could be accomplished so much easier using a parser library like RapidXML. This page is an excellent resource.

The code below is my attempt to read the following XML (yes, a XML file must have a header):

File: demo.xml

     xmlMetadata 

A quick note: rapidxml is consisted only of headers. On my system I unzipped the library to /usr/include/rapidxml-1.13, so the code below could be compiled with:

g++ read_tag.cpp -o read_tag -I/usr/include/rapidxml-1.13/

File: read_tag.cpp

#include 
#include 
#include 
#include 
#include 

using namespace std;
using namespace rapidxml;


int main()
{
    string input_xml;
    string line;
    ifstream in("demo.xml");

    // read file into input_xml
    while(getline(in,line))
        input_xml += line;

    // make a safe-to-modify copy of input_xml
    // (you should never modify the contents of an std::string directly)
    vector xml_copy(input_xml.begin(), input_xml.end());
    xml_copy.push_back('\0');

    // only use xml_copy from here on!
    xml_document<> doc;
    // we are choosing to parse the XML declaration
    // parse_no_data_nodes prevents RapidXML from using the somewhat surprising
    // behavior of having both values and data nodes, and having data nodes take
    // precedence over values when printing
    // >>> note that this will skip parsing of CDATA nodes <<<
    doc.parse(&xml_copy[0]);

    // alternatively, use one of the two commented lines below to parse CDATA nodes,
    // but please note the above caveat about surprising interactions between
    // values and data nodes (also read http://www.ffuts.org/blog/a-rapidxml-gotcha/)
    // if you use one of these two declarations try to use data nodes exclusively and
    // avoid using value()
    //doc.parse(&xml_copy[0]); // just get the XML declaration
    //doc.parse(&xml_copy[0]); // parses everything (slowest)

    // since we have parsed the XML declaration, it is the first node
    // (otherwise the first node would be our root node)
    string encoding = doc.first_node()->first_attribute("encoding")->value();
    // encoding == "utf-8"

    // we didn't keep track of our previous traversal, so let's start again
    // we can match nodes by name, skipping the xml declaration entirely
    xml_node<>* cur_node = doc.first_node("rootnode");
    string rootnode_type = cur_node->first_attribute("type")->value();
    // rootnode_type == "example"

    // go straight to the first Package node
    cur_node = cur_node->first_node("Package");
    string content = cur_node->value(); // if the node doesn't exist, this line will crash

    cout << content << endl;
}

Outputs:

xmlMetadata