[C #] Learn to handle exceptions

Learn to deal with anomalies

C # programmers can use a try block to partition code that might be affected by an exception. The associated catch block is used to handle any resulting exception. A finally block that contains code that runs regardless of try whether an exception is thrown in the block (for example, freeing try resources allocated in a block). A try block requires one or more associated catch blocks or a finally block, or both.

A statement try-catch , a statement try-finally , and a statement are given here respectively try-catch-finally .

Try-catch:

1         Static voidMain (string[] args)2         {3             Try4             {5                 //code that needs to be executed6             }7             Catch(Exception e)8             {9                 //Here you can get to the caught exceptionTen                 //you need to know how you should handle the exception One             } A}

Try-finally:

1             Try 2             {3                 // code 4            } required to execute 5              Finally6            {7                 // code 8 executed after the try block              }

Try-catch-finally:

1             Try2             {3                 //code that needs to be executed4             }5             Catch(Exception e)6             {7                 //Handling Exceptions here8             }9             finallyTen             { One                 //code that executes after a try block (or possibly a catch block) A}

A block with a "memo" that does not come with catch or finally blocks try will cause a compiler error.

catch block to catch exception

　　catchThe block can specify the type of exception to catch. The type specification is called an exception filter. The exception type should be derived from Exception. In general, Exception is not specified as an exception filter unless you know how to handle try any exceptions that might be thrown in a block, or you catch include a throw statement in a block.

Multiple blocks with different exception filters catch can be concatenated together. Multiple catch data blocks are evaluated in the code from the top to the bottom, but only one block of data is executed for each exception that is thrown catch . The first block that best matches the specified exact type or its base class catch is executed. If the catch block does not specify a matching exception filter, the catch block does not have the selected filter (if the statement has one). The block with the most specific (that is, the most derived) exception class needs to be catch placed at the front.

You should catch an exception when the following conditions are true:

• There is a specific understanding of why the exception was thrown, and a specific recovery can be implemented, for example, prompting the user to enter a new file name when capturing a FileNotFoundException object.

• You can create a new, more specific exception and throw the exception.

1         DoubleGetnum (Double[] Nums,intindex)2         {3             Try4             {5                 returnNums[index];6             }7             Catch(IndexOutOfRangeException e)8             {9                 Throw NewArgumentOutOfRangeException ("Sorry, the index you want is out of bounds! ");Ten             } One}

Hopefully, we'll usually handle some exceptions when passing exceptions. In the following example, the catch block is used to add an error log before the exception is thrown again, which is a common practice.

1             Try2             {3                 //try to access system resources4             }5             Catch(Exception e)6             {7                 //Pseudo code: Log error Logs8 log. Error (e);9 Ten                 //and then re-throw the error One                 Throw; A}

release a Finally block of resources

You can use finally blocks to clean up try operations that are performed in a block. If present, the finally block is executed at the end try , after the block and any matching catch blocks. Always runs regardless of whether an exception is thrown or if a block that matches the type of the exception is found catch finally .

You can use finally blocks to free resources (such as file streams, database connections, and graphics handles) without waiting for the garbage collector in the runtime to complete the object. In fact, we recommend using a USE statement.

In the following example, a block is used to finally close try a file that is opened in a block. Note that you check the status of the file handle before closing the file. If the try block cannot open the file, the file handle still has a value null , and the finally block does not attempt to close it. Or, if try the file is successfully opened in a block, the finally block closes the open file.

1         Static voidMain (string[] args)2         {3FileStream fs =NULL;4FileInfo fi =NewSystem.IO.FileInfo ("c:\\ The story of Xiao ER and small three. txt");5 6             Try7             {8FS =fi. OpenWrite ();9Fs. WriteByte (0);Ten             } One             finally A             { -                 //Remember to judge null Oh, otherwise it may trigger other exceptions -                 if(FS! =NULL) the                 { - FS. Close (); -                 } -             } +  -}

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"Original" http://www.cnblogs.com/liqingwen/p/6193999.html

"Reference" Official Microsoft documentation

[C #] Learn to handle exceptions