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POC++: follow-up question on reading from an external file using getline(). How to get a subset of the file data?
 

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  1. POC++: follow-up question on reading from an external file using getline(). How to get a subset of the file data?
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    <p>I need to read in numbers from an external file and store them in a vector of ints. I can do this now thanks to Howard Hinnant and wilhelmtell, who patiently helped figure out why my coding was not working yesterday.</p> <p>I have been trying to figure out how to incorporate an additional feature into the code, but I have exhausted my knowledge of streams and would appreciate some advice.</p> <p>I want to be able to deal with files containing many sets of data. Is it possible to extract only certain data from the file into a vector? I want to end up with several vectors that contain data from different parts of the file. I searched online, but have not seen any mention of this. </p> <p>Here's the code plus an example of a file (let's call it "test") that I want to get data from.</p> <hr> <p><strong>Edit:</strong> <em>I edited the code based on CashCow's advice. I can now get a block out of the data file. But I don't know how to get the block I want. If I run the code as it is, I get a vector that contains the elements 2,5,8 (this is not what I want). To get vectorTwo (4,5,6 in the example I made), I tried adding this around the while statement:</em></p> <pre><code>if( line == "vectorTwo" ) { // The while statement and its contents } </code></pre> <p>It did not work. I did not get any results from running the code (it compiled though). Can anyone see what the problem is? I figured I could use this statement to search for the header for the block of data I need.</p> <hr> <p>//Here are the contents of the example file</p> <p>vectorOne // Identifier for subset of data for one vector</p> <p>'1' '2' '3'</p> <p><strong>vectorTwo</strong> <strong><em>// How would I get this one vector? Or any other one vector?</em></strong> </p> <p>'4' '5' '6'</p> <p>vectorThree // Identifier for subset of data for another vector</p> <p>'7' '8' '9'</p> <p>// Code: The '\'' character is the line delimiter. Everything is ignored up to the first ' and then everything until the next ' is part of a number. This continue until the logic fails (end of file). How can I get it to stop at the end of a data block instead?</p> <pre><code>#include &lt;fstream&gt; #include &lt;iostream&gt; #include &lt;vector&gt; #include &lt;string&gt; #include &lt;sstream&gt; #include &lt;iterator&gt; int main() { std::string line; std::string block; // Edited, from CashCow const std::string fileName = "test.dat"; std::ifstream theStream( fileName.c_str() ); if( ! theStream ) std::cerr &lt;&lt; "Error opening file test.dat\n"; std::vector&lt;int&gt; numbers; // This code is written for one vector only. There would be three vectors for the example file I provided above; one for the vectorOne data in the file, and so on. while (true) { // get first ' std::getline(theStream, line, '\''); // read until second ' std::getline(theStream, line, '\''); std::istringstream myStream( line ); std::getline( theStream, block, '\n' ); // Edited, from CashCow std::istringstream blockstream( block ); // Edited, from CashCow std::getline(blockstream, line, '\''); // Edited, from CashCow int i; myStream &gt;&gt; i; if (myStream.fail()) break; numbers.push_back(i); } std::copy(numbers.begin(), numbers.end(), std::ostream_iterator&lt;int&gt;(std::cout, "\n")); } </code></pre>
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