{"id":667,"date":"2022-05-09T16:56:00","date_gmt":"2022-05-09T09:56:00","guid":{"rendered":"https:\/\/csharptutorial.net\/?page_id=667"},"modified":"2022-06-03T15:08:25","modified_gmt":"2022-06-03T08:08:25","slug":"csharp-try-catch-finally","status":"publish","type":"page","link":"https:\/\/www.csharptutorial.net\/csharp-tutorial\/csharp-try-catch-finally\/","title":{"rendered":"C# try catch finally"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn how to use the C# try...catch...finally<\/code> statement to handle exceptions and clean up resources.<\/p>\n\n\n\n

Introduction to the C# try…catch…finally statement<\/h2>\n\n\n\n

The try...catch<\/a><\/code> statement has an optional finally<\/code> clause as follows:<\/p>\n\n\n

try<\/span>\n{\n    \/\/ execute statement<\/span>\n}\ncatch<\/span> (Exception<\/span> e)\n{\n    \/\/ handle execeptions<\/span>\n}\nfinally<\/span>\n{\n    \/\/ always execute<\/span>\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
When a try...catch<\/code> statement contains a finally<\/code>, it always executes the finally<\/code> block whether an exception occurs inside the try<\/code> block or not:<\/p>\n\n\n\n
  • If no exception occurs inside the try<\/code> block, the control skips over any catch<\/code> block and goes to the finally<\/code> block.<\/li>
  • If an exception occurs inside the try<\/code> block, the appropriate catch<\/code> clauses are executed followed by the execution of the finally<\/code> block.<\/li><\/ul>\n\n\n\n
    It’s important to note that even if the try<\/code> clause has a return<\/code> statement, the finally<\/code> block will always execute.<\/p>\n\n\n\n
    Also, the finally<\/code> block cannot contain a return<\/code> statement. Otherwise, the program will fail to compile.<\/p>\n\n\n\n
    In practice, you often use the finally<\/code> block to clean up the resources such as closing a stream or a database connection.<\/p>\n\n\n\n
    C# try…catch…finally statement example<\/h2>\n\n\n\n
    Let’s take some examples of using the try...catch..finally<\/code> statment.<\/p>\n\n\n\n
    1) Using the C# try…catch…finally statement example<\/h3>\n\n\n\n
    The following program reads a text file line by line and displays the file contents to the console. It uses the try...catch...finally<\/code> statement to handle exceptions:<\/p>\n\n\n
    StreamReader? reader = null<\/span>;\ntry<\/span>\n{\n    reader = new<\/span> StreamReader(@\"C:\\csharptutorial\\test.txt\"<\/span>);\n    string? line = reader.ReadLine();\n    while<\/span> (line != null<\/span>)\n    {\n        Console.WriteLine(line);\n        line = reader.ReadLine();\n    }\n}\ncatch<\/span> (Exception<\/span> e)\n{\n    Console.WriteLine($\"Error: {e.Message}\"<\/span>);\n}\nfinally<\/span>\n{\n    \/\/close the file<\/span>\n    if<\/span> (reader != null<\/span>) reader.Close();\n}<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
    In this example, the finally<\/code> block closes the stream reader whether an exception occurs inside the try<\/code> block or not.<\/p>\n\n\n\n
    2) Using the C# try…catch…finally statement with the return statement<\/h3>\n\n\n\n
    The following illustrates the control flow of the program when using a return<\/code> statement inside the try<\/code> block:<\/p>\n\n\n
    \n\nint Test()\n{\n    int result = 100<\/span>;\n    try<\/span>\n    {\n        return<\/span> result;\n    }\n    catch<\/span> (Exception<\/span> e) \n    {\n        Console.WriteLine(e.Message);\n    } \n    finally<\/span>\n    {\n        result = 200<\/span>;\n        Console.WriteLine(\"Execute the finally block...\"<\/span>);\n    }\n\n    \/\/ these statement won't execute<\/span>\n    Console.WriteLine(\"Bye!\"<\/span>);\n    return<\/span> result;\n}\n\nConsole.WriteLine(Test());<\/code><\/span>Code language:<\/span> PHP<\/span> (<\/span>php<\/span>)<\/span><\/small><\/pre>\n\n\n
    Output:<\/p>\n\n\n
    Execute the finally<\/span> block...\n100<\/span><\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>\n\n\n
    In this example, the program returns the result<\/code> variable in the try<\/code> block. The program also executes the finally<\/code> block. However, it ends immediately as long as it reaches the end of the finally<\/code> block.<\/p>\n\n\n\n
    Summary<\/h2>\n\n\n\n
    • Use the C# try...catch...finally<\/code> block to handle exceptions and clean up the resources.<\/li>
    • The finally<\/code> block always executes whether an exception occurs in the try<\/code> block or not.<\/li><\/ul>\n
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