Reading a line from a file

This is a discussion on Reading a line from a file within the C++ Programming forums, part of the General Programming Boards category; I'm trying to read in a file and store each line in the file into an array? I need some ...

  1. #1
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    Reading a line from a file

    I'm trying to read in a file and store each line in the file into an array? I need some help, I think im doing something wrong



    Code:
    int main()
    
    {
    ifstream input;
    ofstream output;
    int count=0;
    string word;
    char inFileName[20];
    char outFileName[20];
    cout << "Enter the input file name >> ";
    cin >> inFileName;
    cout << "Enter the output file name >> ";
    cin >> outFileName;
    
    
    input.open(inFileName);
    if(input.fail())
    	{
    	cout << "Unable to open " << input << " now exiting." << endl;
    	exit(1);
    	}
    
    
    output.open(outFileName);
    if(output.fail())
    	{
    	cout << "Unable to open " << output << " now exiting." << endl;
    	exit(1);
    	}
    cout << "Enter the number of entry to be read >>";
    cin >> count;
    char temp[count];
    for (int i =0; i <count; i++)
    	{
    	input >> temp[count];
    	count++;
    	}
    for(int i =0; i <count; i++)
    {
    cout << temp[count]<< endl;
    }
    input.close();
    output.close();
    return 0;
    }

  2. #2
    Registered User major_small's Avatar
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    are you getting any errors?
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  3. #3
    Registered User jlou's Avatar
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    Problem one:

    You cannot create an array of chars with a variable size the way you are trying to do it: char temp[count]; is wrong if the compiler doesn't know what count is (which in your case it doesn't). The solution is to use new:

    char* temp = new char[count];
    // ... All your code that uses temp
    delete [] temp;


    Problem two:

    Inside your for loops, you should be using i, not count as the index to the array.

    Problem three:

    You aren't reading in a line at a time, you are reading a character at a time from the input file. Fix your other two problems first, and then try and figure out this one.

  4. #4
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    is their a way to use "getline" and store into an array?

  5. #5
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    sure.

    fin.getline(CstyleStringArray[i], MaxCharToRead, terminatingChar);

    or

    fin.getline(STLstringVector[i], terminatingChar);

    where fin is an open stream capable of reading from file and associated with a file. The other parameter names seem self explanatory.

  6. #6
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    i'm still have a lil hard time using getline. All i want to do is read in a file that contains a sentences for each line. And store that stentences into an array. so i can print it out.

  7. #7
    Registered User jlou's Avatar
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    Do you really need to store each line, or just the line the user asks for?

    By the way, a C-style string is an array itself (actually a null terminated character array), but I will just refer to it as a string. If you only need one line, you don't need a separate array of strings. You can just loop through the input file a line at a time until you reach the line that the user asked for.

    This is one way to get a line from a file into a C-style string and then output the string:
    Code:
    char currentSentence[100]; // Maximum size of line is 100 characters.
    input.getline(currentSentence, 100); // Get either 99 characters + null, or the entire line, whichever is first.
    cout << currentSentence << endl;  // Output the string
    If you can understand that code, then you should be able to use it in your program.

    If you do want to store every line as an array of sentences, you will want to use an array of strings. In this case, that would be an array of character arrays. That is more complicated, so I won't give you details on that unless you really need to do it.

    And as always, if you can use the standard string class (std::string) you would probably have an easier time getting this to work.

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