Conteúdo do Curso

C# Beyond Basics

1. Additional Structures & File Handling

What are Lists?Practicing List Declaration List Methods What are Dictionaries?Practicing Dictionaries Reading Files using StreamReader Reading Files using File Methods Writing Files Error Handling Practicing Error Handling

2. Structs & Enumerators

What are Structs?Defining & Using a Structure Practicing Structs Structs with Other Data Structures Struct Methods Correctly Accessing Fields in Struct Methods Practicing Methods Struct Constructors Practicing Constructors Enumerators Practicing Enumerator

3. Introduction to Object-Oriented Programming (OOP)

What is Object-Oriented Programming?Defining Classes Practice: Creating Classes Class Objects Class Objects vs Struct Objects Practice: Objects Class Methods Practice: Methods Class Constructors Practice: Constructors

4. OOP Essentials

Derived Classes Derived Classes Practice Common Access Modifiers Access Modifiers Practice The `static` Keyword Practicing `static` Keyword Method Overloading Method Overloading Practice

5. OOP Principles

What are the Principles of OOP?Inheritance Practicing Inheritance Polymorphism Practicing Polymorphism Encapsulation Encapsulation Practice Abstraction Abstraction Practice What's Next?

Reading Files using StreamReader

We can open and read files using the C# programming language.

For reading a file, we create a new StreamReader object. The StreamReader object takes in the path of the file.

index


              1
            
StreamReader fileVarName = new StreamReader(fullPath);

Here fileVarName represents the variable name in which we will store the StreamReader object, and fullPath is supposed to be the full path of the file in the form of a string.

For-example we want to open a file "text.txt" on Desktop which has the path C:/Users/Admin/Desktop/text.txt:

index


              1
            
StreamReader textFile = new StreamReader("C:/Users/Admin/Desktop/text.txt");

Consider the text.txt file has the following content:

text


              12345
            
This
is
some
example
text

A StreamReader object has a ReadLine method which reads one line from the file and returns it:

index


              1234
            
var textFile = new StreamReader("C:/Users/Admin/Desktop/text.txt");

string line = textFile.ReadLine();
Console.WriteLine(line);

Output:

The ReadLine method automatically switches the cursor to the next line so when it's called again, it reads the next line if there is any, otherwise it simply returns null (nothing):

index


              12345678
            
var textFile = new StreamReader("C:/Users/Admin/Desktop/text.txt");

Console.WriteLine(textFile.ReadLine()); // This
Console.WriteLine(textFile.ReadLine()); // is
Console.WriteLine(textFile.ReadLine()); // some
Console.WriteLine(textFile.ReadLine()); // example
Console.WriteLine(textFile.ReadLine()); // text
Console.WriteLine(textFile.ReadLine()); // NULL

Output:

For reading all the lines from a file we can use the while loop with a condition which checks if the next line is null or not. Following is a simple way we can do that:

index


              12345678
            
var textFile = new StreamReader("C:/Users/Admin/Desktop/text.txt");

string line = textFile.ReadLine();
while(line != null)
{
    Console.WriteLine(line);
    line = textFile.ReadLine();
}

Output:

We can make the above code a bit neater using a trick, for that lets take a look at the assignment statements. An assignment statement has a return value as well, which is the value that is being assigned. It can be understood with an example:

index


              12
            
int a;
Console.WriteLine(a = 7);

Output:

It outputs 7 because the statement a = 7 returns 7 which is the value being assigned to a.

We can use this information to do some creative things like assigning the same value to multiple variables in a single statement:

index


              123456789
            
int a = 1;
int b = 1;
int c = 1;

a = b = c = 9;

Console.WriteLine(a);
Console.WriteLine(b);
Console.WriteLine(c);

Output:

Using this information, we can modify the file reading code to make it shorter removing unnecessary code:

index


              1234567
            
var textFile = new StreamReader("C:/Users/Admin/Desktop/text.txt");

string line;
while((line = textFile.ReadLine()) != null)
{
    Console.WriteLine(line);
}

Inside the condition we first used an assignment statement line = textFile.ReadLine() which automatically updates the line variable and then checks if it's null from the statement's return value.

After reading the file we must also close it using the Close method, otherwise it can potentially cause memory leaks or the file can be locked and become inaccessible from other places as long as the program is running.

The final code will look something like this:

index


              123456789
            
var textFile = new StreamReader("C:/Users/Admin/Desktop/text.txt");

string line;
while ((line = textFile.ReadLine()) != null)
{
    Console.WriteLine(line);
}

textFile.Close();

Tudo estava claro?

Obrigado pelo seu feedback!

Seção 1. Capítulo 6