Using string class member functions - c++

Question

Here's my task and below is most of the code I already wrote:
Develop the program so that it finds and extracts specified items from the xmlstring file using start and end tags. Now we find and extract and display first the location information and then the temperature information.
Location can be found between the tags <location> and </location>. The temperature is between the tags <temp_c> and </temp_c>.
To make it easy to find whatever information from the, xml-string write a function that takes the xml-string and the "inner" text (same for start tag and end tag) of the tags as parameters and returns the text from between the start tag and end tags. If either start or end tag is not found the function must return "not found".
Note that when you search for the tag you must search for the whole tag (including angle brackets) not just the tag name that was given as parameter.
For example, if you wanted to find the location
location = find_field(page, "location");
and to get the temperature you could call it as follows:
temperature = find_field(page, "temp_c");
MY CODE:
#pragma warning (disable:4996)
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
string find_field(const string& xml, string tag_name);
int main() {
string page, line, location, temperature;
ifstream inputFile("weather.xml");
while (getline(inputFile, line)) {
page.append(line);
line.erase();
}
location = find_field(page, "location");
temperature = find_field(page, "<temp_c>");
cout << "Location: " << location << endl;
cout << "Temperature: " << temperature << endl;
}
string find_field(const string& xml, string tag_name)
{
string start_tag = "<" + tag_name + ">";
string end_tag = "<" + tag_name + ">";
return "not found";
}
SPECIFIC QUESTION
When I run the program it says:
Location: not found
Temperature: not found
Just not found. But it doesnt show the data that is in the file. How can I fix it? Thanks

Answer 1

I will not solve this completely for you, because I assume this is a task for you to actually learn, but I will give you some guidance.
In C++ you work on strings with iterators or offsets (positions). Since you are starting, I would suggest to first get familiar with offsets.
Basically, you need to search for the positions of start_tag and end_tag in your xml string and then return what is in between. The std::string class has a find method (http://www.cplusplus.com/reference/string/string/find/). You use it to find the start position of the search string. Additionally, you will probably need the length method (http://www.cplusplus.com/reference/string/string/length/) for position calculation and the substr method (http://www.cplusplus.com/reference/string/string/substr/) to get the interesting part.
Your pseudo logic of the find could be:
Find the start position of the start_tag in xml
Calculate the end position of the start_tag (start position + length of start_tag)
Find the start position of the end_tag in xml
Return sub-string between the two positions (the length is the difference between start position of end_tag and end position of start_tag)
Of course you need to check if the positions are valid before step 4 and if not return the "Not found".
Additionally, please consider Scheff's third comment on your question, that the end_tag starts with </ and that you need to call find_field without the angle brackets around your search string because you add them later in the function.
I hope this helps you find a solution.
Here is a very incomplete starter example:
string find_field(const string& xml, string tag_name)
{
std::string start_tag = "<" + tag_name + ">";
std::string end_tag = "</" + tag_name + ">";
size_t start_tag_start_pos = xml.find(start_tag);
// make some sanity checks to the position here (find returns std::string::npos if start_tag wasn't found)
size_t start_pos_of_interesting_string = start_tag_start_pos + start_tag.length();
// you can find the start_pos of the end tag similarly
// don't forget sanity checks
// calculate the length of between start and end tag
return xml.substr(start_pos_of_interesting_string, /* you need to add the length of the interesting string here*/);
}