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Program to read file

  1. Dec 9, 2007 #1
    hi! i was writing a program which asks the user to input the file name. the program then reads the file and prints out how many times each characeter has occured in the file(uppercase and lowercase are different). Pls help me out.
    this is what i have got-i know this is not correct.

    #include<iostream>
    #include<fstream>
    #include<stdlib.h>

    using namespace std;

    int main()
    {
    fstream file_ptr;
    char filename[81];
    int a = 65;
    int e=0;
    char number[58]={0};
    for(int i=0; i<58; i++)
    {
    number=a;
    a++;
    }
    // Get name of file
    cout << "Enter filename : ";
    cin.getline(filename,81);
    // Open data file for READING
    cout << "Opening file "<< filename << endl;
    file_ptr.open(filename, ios::in);
    if (!file_ptr.good())
    {
    //The file could not be opened
    cout << "ERROR - file " << filename << " could not be opened";
    exit(1);
    }
    // READ data from file until the end-of-file (EOF) is reached.

    do {
    file_ptr >> number;
    cout << "Read " << number << " from file." << endl;
    } while(file_ptr.peek()!=EOF);
    // Close file
    cout << "Closing file " << filename << endl;
    file_ptr.close();
    system("pause");
    return 0;
    }
     
  2. jcsd
  3. Dec 9, 2007 #2

    KTC

    User Avatar

    Code (Text):
    char filename[81];
    Why 81? What's 81 char big? Don't use magic number.

    Code (Text):
    int a = 65;
    Why 65? What's 65? Don't use magic number. You don't need to tell the program what it's internal representation is in numerically for characters. Use char's and it'll work it out itself.

    Code (Text):
    int e=0;
    What's e? Where have you used it?

    Code (Text):
    char number[58]={0};
    Why 58? What's 58? Don't use magic number.

    Code (Text):
    for(int i=0; i<58; i++)
    {
    number[i]=a;
    a++;
    }
    Don't need that.

    Code (Text):
    cin.getline(filename,81);
    Use std::string, and not some random arbitrary length for the filename.

    Code (Text):
    do {
    file_ptr >> number;
    cout << "Read " << number << " from file." << endl;
    } while(file_ptr.peek()!=EOF);
    >> reads in from the first non-whitespace character until the next non-whitespace character. number confusing though you've made it, is char array of 58 char's long. You're wanting to read in each character one at a time, and count it. Why are you reading in phase at a time?
     
  4. Dec 9, 2007 #3
    hmm, man, I hate C++. C++ is way too overloaded (it's a joke). Try placing comments or exlanations on each part of your code, so you, yourself, and others know what a section does. Look at all those questions by KTC. Try simplifying your code, or remove code that isn't really needed. And I believe, C++ has helper functions for getting on a character by character basis. Anyway, I'll check again and post here another time.
     
  5. Dec 9, 2007 #4
    this is something different which i wrote

    #include<iostream>
    #include<fstream>
    #include<stdlib.h>

    using namespace std;

    int main()
    {
    fstream file_ptr;
    char filename[81];
    // Get name of file
    cout << "Enter the filename (make sure that the test file and the program is in the same directory): ";
    cin.getline(filename,81);
    // Open data file for READING
    cout << "Opening file "<< filename << endl;
    file_ptr.open(filename, ios::in);
    if (!file_ptr.good())
    {
    //The file could not be opened
    cout << "ERROR - file " << filename << " could not be opened";
    exit(1);
    }
    int a = 65;
    char number[58]={0};
    for(int i=0; i<58; i++)
    {
    number=a;
    a++;
    }
    int x[58]={0};
    char c;
    // READ data from file until the end-of-file (EOF) is reached.
    while(file_ptr.eof()==0)
    {
    file_ptr.get(c); //reading character
    for(int i=0; i<58; i++)
    {
    if(number==c)
    {
    x=x+1;
    break;
    }
    }
    }
    for(int i=0; i<58; i++)
    {
    cout<<number<<"="<<x<<endl;
    }

    // Close file
    cout << "Closing file " << filename << endl;
    file_ptr.close();
    system("pause");
    return 0;
    }
     
  6. Dec 9, 2007 #5
    i took 65 because 65 is ASCII equivalent of 'a'. as i wnt to get all the alphabets(both uppercase and lowercase) so i used size of d array as 58.
    65 + 58 =123 which is ASCII equivalent of 'Z'.

    i still dont know how to correct the filename part in d code.
     
  7. Dec 9, 2007 #6

    jtbell

    User Avatar

    Staff: Mentor

    When reading files using a "while" loop in C++, it is almost never a good idea to use the eof() member function or the predefined EOF symbol, because it gives you "true" only after the program has tried to read past the end of file and failed. Therefore the loop makes one more cycle after the last real data item, giving you some garbage input.

    In your case, the usual way to read one character at a time is:

    Code (Text):

    while (file_ptr.get(c))
    {
        // do your stuff with c here
    }
     
    When you use any of the standard C++ input operations in a boolean context, it evaluates as "true" or "false" depending on whether the operation succeeded or not, in addition to actually performing the input operation. Therefore, when file_ptr.get() tries to read past the last character in the file, it fails, and the loop terminates immediately without trying to do anything with the garbage that is now in c.

    The appropriate way to use eof() is to test whether the loop ended because of end of file or some other kind of input error:

    Code (Text):

    while (file_ptr.get(c))
    {
        // do your stuff with c here
    }

    if (file_ptr.eof())
        cout << "End of file reached normally." << endl;
    else
        cout << "There was an input error." << endl;
     
     
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