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Using input files with Xcode

  1. Apr 9, 2009 #1
    I am in a C++ class, programming a command line utility, and I can't figure out how to open and read from an input file in xcode. any help?
  2. jcsd
  3. Apr 9, 2009 #2
    Is this a console app or an OS X (Carbon/Cocoa) app?

    If it's a console app you want to use the ifstream classes. Look for something like "ifstream example" on google. (Alternately you can use fopen/fclose and the related C methods.)
  4. Apr 9, 2009 #3
    Right. It's in the console. Here is what I have:

    string filecheck(string& tubein)
    ifstream InFile;

    cin.clear(); //resets input stream if it is in the fail state mode
    cout<<"Enter the input file name: ";
    cin>>tubein; //stores filename
    InFile.open(tubein.c_str()); //priming read for filename validity loop
    while(!InFile) //filename validity loop
    cout<<"\n Error: Filename invalid. Please Try again."<<endl<<endl;
    cout<<"Enter the input file name: ";
    InFile.close(); //closes input stream so it can be used by other functions
    return tubein;
  5. Apr 9, 2009 #4
    The problem is most likely that the "present working directory" when your program runs is not what you think it is. You need to either:

    - Specify the full path of the file, i.e. something like /Users/oops/filename.txt

    - Move the file you want to open into the "present working directory" of your program. I believe you can find this by looking in the "build" directory which is in the same directory as your xcode file, then looking inside "debug".
  6. Apr 9, 2009 #5
    No luck. The input stream goes in to the "fail-state" mode when it reads it in. Do I need to make any stipulations in the project to add the files in? (The files are .txt files)
  7. Apr 9, 2009 #6
    Stipulations in the project aren't what you want in this case, not for a console app.

    You need to figure out what the present working directory is. Try sticking a system("pwd"); at the top of your main() or something?

    You may also want to try printing back the filename you are trying to open. For example the code you've got there will fail if there are spaces in the filename.
  8. Apr 9, 2009 #7
    /Users/.../build/Debug/P11_in1.txt is the directory. What should I do about the spaces in the directory?

    I am going to be typing in the filename quite frequently is there some way I can shorten the process, besides typing in the ENTIRE directory
  9. Apr 9, 2009 #8


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    Staff Emeritus
    Science Advisor
    Gold Member

    Learn how to use your shell.

    - Warren
  10. Apr 9, 2009 #9
    Thanks for the encouragement :)

    I totally forgot about that! either way it's not working...
  11. Apr 9, 2009 #10


    User Avatar

    Staff: Mentor

    Why are you trying to compile a console app using Xcode, anyway? If you compile the code using the g++ command at the command line, your program looks for input files in your current working directory which is probably the place where your source code and compiled executable are.

    Code (Text):

    [Jons-Mac-Pro:~/Documents/c++] jtbell% ls
    csv.cpp     csv.dat
    [Jons-Mac-Pro:~/Documents/c++] jtbell% cat csv.cpp
    // Demonstrates using getline() and a stringstream to read a file
    // of comma-separated values.

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

    using namespace std;

    int main ()
        ifstream inFile ("csv.dat");
        string line;
        int linenum = 0;
        while (getline (inFile, line))
            cout << "\nLine #" << linenum << ":" << endl;
            istringstream linestream(line);
            string item;
            int itemnum = 0;
            while (getline (linestream, item, ','))
                cout << "Item #" << itemnum << ": " << item << endl;

        return 0;
    [Jons-Mac-Pro:~/Documents/c++] jtbell% cat csv.dat
    [Jons-Mac-Pro:~/Documents/c++] jtbell% g++ csv.cpp -o csv
    [Jons-Mac-Pro:~/Documents/c++] jtbell% ls
    csv csv.cpp     csv.dat
    [Jons-Mac-Pro:~/Documents/c++] jtbell% ./csv

    Line #1:
    Item #1: 8/29/2008
    Item #2: 19.54
    Item #3: 19.6
    Item #4: 19.28
    Item #5: 19.38
    Item #6: 11204900
    Item #7: 19.38

    Line #2:
    Item #1: 8/28/2008
    Item #2: 19.48
    Item #3: 19.76
    Item #4: 19.38
    Item #5: 19.65
    Item #6: 11729500
    Item #7: 19.65
    [Jons-Mac-Pro:~/Documents/c++] jtbell%
  12. Apr 9, 2009 #11
    xcode is just calling g++ anyway, there is no harm in using it to compile.

    But jtbell is right, it is definitely the case that if you run your console app from the command line rather than via xcode you will not have this uncertainty about pwd.

    If there are potentially spaces in the file name, you should use cin.getline instead of cin >>. cin >> will stop listening at the first whitespace character.
  13. Apr 9, 2009 #12
    ok, I think I fixed the problem. Apparently, you need to put the argument 'int argc, char * const argv[]' in int main. I didn't use this before, and I have noticed that xcode's template always has that as the argument. Anyone know why this works?
  14. Apr 10, 2009 #13


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    Staff: Mentor

    I have no idea why this would make a difference for you, if you're not actually using the command-line argument variables argc and argv[] in your program.
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