[RESOLVED] File I/O and String question
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  1. #1
    Join Date
    Feb 2012
    Posts
    9

    [RESOLVED] File I/O and String question

    i have a text file called example.txt and it contains the following lines.

    21 squarepants,Spongebob
    115 barack,Obama
    7 Carter,Mc Farland
    227 Abraham Carter,Lincoln

    Basically, I have to read into this file, take the last name and capitalize it. I need to have the capitalized last name outputed onto another text file, which i called outfile.
    I just started c++ and the class is basically self-teaching. I am not an expert, but i do have 2 approaches to this program. I just need help writing the code.

    My first approach is if i can use a substring and take out the string between the first space and the comma. I tried it but when compiling it never seems to work. I feel it has something to do with my syntax. Another possible approach could be if i can clear all the numbers and get the postion of the comma and clear everything after the comma. That way all i have left is a string with just the last name. Well, below is what I have so far. I have included both of my approaches, so someone can correct my code.

    Thank You in advance for your help. I would really appreciate it!

    #include <iostream>
    #include <fstream>
    #include <string>

    using namespace std;

    int main ()
    {

    string line, str, str1;
    ifstream infile; //object for reading from a file
    ofstream outfile; // object for writing to a file
    size_t pos;

    infile.open ("example.txt", ios::app); //open a file for writing
    outfile.open ("results.txt");

    if (infile.is_open()) // if file was able to open
    {
    while (!infile.eof())

    cout << (char) infile.get();
    getline(infile,line); //print out the lines in the entire file

    str1 = line;

    //Approach #1
    pos = str.find(" "); // position of " " in str
    pos = str.find(","); // position of "," in str
    str1 = str.substr (" ", ","); // get the string between the first
    space and the comma


    // Approach #2
    pos = str.find(" "); // position of " " in str
    pos = str.find(","); // position of "," in str
    str2 = str.substr (pos); // get everything after the comma
    str2.erase(pos); // erase everything after the comma. Is this line
    even correct?

    str1=last;
    cout << uppercase << last << endl;
    outfile << last << endl;

    infile.close();
    outfile.close();
    }
    else
    {
    cout << "Error opening file";
    }
    return 0;
    }

  2. #2
    Join Date
    Jan 2006
    Location
    Singapore
    Posts
    6,244

    Re: File I/O and String question

    Your idea to find the position of the space and then the comma is workable, but your implementation is wrong. For example, you are overwriting the pos variable prematurely.
    C + C++ Compiler: MinGW port of GCC
    Build + Version Control System: SCons + Bazaar

    Look up a C/C++ Reference and learn How To Ask Questions The Smart Way
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  3. #3
    Join Date
    Feb 2012
    Posts
    9

    Re: File I/O and String question

    Ya I figured my implementation was wrong. I just started C++.
    I can't seem to get it right when implementing with substring.

    How would you recommend to do it?

  4. #4
    Join Date
    Jan 2006
    Location
    Singapore
    Posts
    6,244

    Re: File I/O and String question

    I would expect something like this:
    Code:
    string line;
    while (getline(infile, line))
    {
        string::size_type pos1 = line.find(' ');
        if (pos1 != string::npos)
        {
            ++pos1;
            string::size_type pos2 = line.find(',', pos1);
            if (pos2 != string::npos)
            {
                string surname = line.substr(pos1, pos2 - pos1);
                // ...
            }
        }
    }
    C + C++ Compiler: MinGW port of GCC
    Build + Version Control System: SCons + Bazaar

    Look up a C/C++ Reference and learn How To Ask Questions The Smart Way
    Kindly rate my posts if you found them useful

  5. #5
    Join Date
    Feb 2012
    Posts
    9

    Question Re: File I/O and String question

    this is what i have so far. The only problem is that it outputs only the last name for the first line and not the last names in the next 3 lines. shouldn't my while loop get the next line and repeat the positions again?



    #include <iostream>
    #include <fstream>
    #include <string>

    using namespace std;

    int main ()
    {

    string line, str, str1;
    ifstream infile; //object for reading from a file
    ofstream outfile; // object for writing to a file
    size_t pos;

    infile.open ("example.txt", ios::app); //open a file for writing
    outfile.open ("results.txt");

    if (infile.is_open()) // if file was able to open
    {

    string line;
    while (getline(infile, line))
    {
    string::size_type pos1 = line.find(' '); //pos1 is the position of the first space
    if (pos1 != string::npos)
    {
    ++pos1;
    string::size_type pos2 = line.find(',', pos1); //pos2 is the position of the comma
    if (pos2 != string::npos)
    {
    string last = line.substr(pos1, pos2 - pos1); //remove everything before the first space
    cout << uppercase << last << endl;
    outfile << last << endl;
    }
    }

    infile.close();
    outfile.close();
    }
    }
    else
    {
    cout << "Error opening file";
    }
    return 0;
    }

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