File Handling

Using C# we can handle files and folders present in the local drive of the system. This function of handling files and folders using C# is known as File Handling. When you open a file for reading or writing, it becomes stream. Stream is a sequence of bytes traveling from a source to a destination over a communication path. All files and folders related classes available in C# are present inside System.IO namespace. We'll learn more about this using code examples.

NOTE:
In order to handle files in a folder, we need to know the folder path. If we copy folder path and store it inside a string, system will start to show error because compiler will get confused with Escape sequences. In order to come out of this, while storing path we need to always use @ symbol before "*PATH*"

CODE

EG 1 . Reading, Writing, Deleting files using C# Code.

//Files and Folders related classes available in C# are present inside following namespace
using System.IO;

namespace projectName{
    class Program{
        static void Main() {
            //------ 1. Printing all file names in Console ------
            string folderPath = @"D:\Personal\Works";
            string[] folderFiles = Directory.GetFiles(folderPath);
            foreach (string folderFile in folderFiles) {
                Console.WriteLine(folderFile);
            }

            //------ 2. Printing only Notepad file names in Console ------
            string folderPath = @"D:\Personal\Works";
            string[] folderFiles = Directory.GetFiles(folderPath, "*.txt");
            foreach (string folderFile in folderFiles) {
                Console.WriteLine(folderFile);
            }

            //------ 3. Deleting all Notepad files in a folder ------
            string folderPath = @"D:\Personal\Works";
            string[] folderFiles = Directory.GetFiles(folderPath, "*.txt");
            foreach (string folderFile in folderFiles) {
                File.Delete(folderFile);
            }

            //------ 4. Creating New file in the folder ------
            File.Create(@"D:\Personal\Works\CodersCapsule.txt");

            //------ 5. Writing content inside file using code ------
            string fileLocation = @"D:\Personal\Works\CodersCapsule.txt";
            File.WriteAllText(fileLocation, "hello there");

            //------ 6. Appending content inside file using code ------
            string fileLocation = @"D:\Personal\Works\CodersCapsule.txt";
            File.AppendAllText(fileLocation, "We are studying File Handling");

            //------ 7. Printing 17th multication table in file using code ------
            string fileLocation = @"D:\Personal\Works\CodersCapsule.txt";
            int tableNumber = 17;
            int limit = 30;
            for (int i = 1; i <= limit; i++) {
                File.AppendAllText(fileLocation, tableNumber + " * " + i + " = " + tableNumber * i + "\n");

            //------ 8. Reading File and printing out in console ------
            string fileLocation = @"D:\Personal\Works\CodersCapsule.txt";
            string[] Lines = File.ReadAllLines(fileLocation);
            foreach (string Line in Lines) {
                Console.WriteLine(Line);
            }
        }
    }
}

CODE EXPLANATION
In the above code, we've taken Works folder present inside Personal folder of Local Drive D. You can create your own path and pass it to folderPath string.

1. We created a string variable called folderPath where we stored the path of Works folder what we going to handle. We used GetFiles() method present inside Directory class to get all the files present inside folder. Now collection of file names(Collection of string values) need to be stored so we are creating a new string[] called folderFiles and stored all file names. Once after doing this we printed out all values stored inside that string[] folderFiles using foreach loop.

2. While getting file names inside GetFiles() method itself we specified what files need to be taken by giving the extension of that file. Here i need to take only the notepad files so we mentioned .txt extension as the second argument of GetFiles() method. Now system will take only the notepad files present inside Works folder. Other operations are same as that of Printing all file names in console.

3. Function wise it is same as that of First 2 explanations, Here instead of printing out file names in Console, we used Delete() method inside File class to delete all the notepad files.

4. In order to create new file using C# code, we used Create() method inside File class. While creating new files we need to cleary mention the path, file name with its extension. If path what we mentioned is incorrect, system will throw run time error stating 'Could not find a part of the path'.

5. We used WriteAllText() method present inside File class to write content inside the file. WriteAllText() method will get 2 arguments. 1st argument is the file location, 2nd argument is the content what we need to write. If we pass both arguments correctly system will simply write given content to the mentioned file. If already some text present inside that file, WriteAllText() method will delete all those text and write the content what we've given.

6. Function wise it is same as that of 5th code explanation, the only difference here is WriteAllText() method will delete the already existing content inside the file and write newly given content inside it. If we use AppendAllText() method, system will keep all the already existing contents and simply append the newly given content inside it.

7. Using some above mentioned classes and methods we printed out 17th multiplication table upto the limit of 30. The logic is same as that of printing out multiplication table what we studied in previous articles. The only difference is, Here instead of printing out multiplication table in console we printed out values in the notepad file using AppendAllText() method.

8. We studied how to Write, Append content to a file. Let's see how to read File. In order to read a file we need to use ReadAllLines() method inside File class. Once system read all lines from file it will have collection of string values so we created a string[] called Lines where we stored all the lines which we read from the file. Now using foreach loop we printed out all the values stored inside Lines in the console.

Exercises
1. Get number of rows value from user in console, Print Triangle shape using * in Notepad file.
2. Get required values from user in console, Calculate Torque required to raise load. Print output in Notepad file.

(Click Here, For more exercises)