C program debugging and exception handling (try catch)

Preface ：

This is an article worthy of your collection . When we are doing form applications or other programs, we will inevitably encounter some BUG, Some inexplicable effects when you run , Or the system directly reports an exception ,C# It provides a powerful exception handling mechanism , It is used to handle errors that may be generated by the application or other exceptions that may cause execution abort , Let's learn this article together , About debugging and exception handling . Okay , It's time to learn .

Once a day , Study makes me progress

1. Program debugging

1.1 Common mistakes

We are in development , Program debugging is an effective way to check and verify that it can run normally . It is inevitable to encounter some errors in writing programs , In order to solve the error, we need to debug the running program , Find out the root cause of the error . There are three common error messages ：

1. Compile error ： It refers to the errors in the compilation process of the program . Common grammatical errors , Missing parentheses, semicolons and so on .

2. Logic error ： When the application does not execute as expected, it will produce logical errors . This kind of grammar is generally right , Due to the wrong Algorithm , If the result is wrong , The formula is not equal . This kind of mistake is the hardest .

3. Running error ： It refers to the illegal sending operation or the failure of some operations during the operation of the program . If the file to be opened cannot be found , Memory leak , Divide by zero. These exceptions can only be expressed when running .

1.2. Debugging method

One method we often use when debugging programs is to use breakpoints . When we operate ： Insert breakpoints ---》 Debug to breakpoint ----》 Delete breakpoints . There are three shortcut keys when using breakpoints ：F11： Operate sentence by sentence , Execute a line of code ,F10： Process by process operation , Execute a piece of code ,shift+F10： Perform the jump operation

2. Exception capture and handling

Exceptions are problems that occur during program execution .C#  An exception in a program is a response to a special situation that occurs when the program runs , For example, try dividing by zero . Exceptions provide a way to transfer control of a program from one part to another .C#  Exception handling is based on four keywords ：

try

、

catch

、

finally

  and  

throw

.

// Concept
try： One  try  Block identifies a block of code for a specific exception that will be activated . One or more heels  catch  block .
catch： The program catches the exception through the exception handler .catch  The keyword represents the capture of an exception .
finally：finally  Block is used to execute a given statement , The exception is executed whether it is thrown or not . for example , If you open a file , No matter whether there is an exception or not, the file will be closed .
throw： When problems arise , The program throws an exception . Use  throw  Keyword to complete .
// usage
try ... catch{// Exception handling code } // Capture exception , Can be more catch
try ... finally{ // Used to eliminate try  Any resources allocated in the block and   Run any code that must be executed even when an exception occurs } // Clear exceptions
try ... catch ... finally //  Handle all exceptions , The combination of the first two
// You need to throw an object
If the exception is derived directly or indirectly from  System.Exception  class , You can throw an object . You can go to  catch  Block the use of  throw  Statement to throw the current object , As shown below ：
Catch(Exception e)
{
 ...
 Throw e
}


2.1 Exception classes understand

Understand some common exception classes , By the way Exception Display all the exception classes of .

// Common exception classes
Exception： Base class for all exception objects .
SystemException： Base class for all errors generated at runtime .
IndexOutOfRangeException： When the subscript of an array is out of range, the runtime raises .
NullReferenceException： Raised by the runtime when an empty object is referenced .
InvalidOperationException： When the call to a method is invalid for the current state of the object , Caused by certain methods .
ArgumentException： Base class for all parameter exceptions .
ArgumentNullException： When the parameter is empty ( Don't allow ) Under the circumstances , Raised by method .
ArgumentOutOfRangeException： When the parameter is not within a given range , Raised by method .
InteropException： The goal is or occurs in CLR The base class of exceptions in the external environment .
ComException： contain COM Class HRESULT Abnormal information .
SEHException： encapsulation Win32 Structural exception handling information exception .
SqlException： Encapsulates the SQL Abnormal operation .
// other Exception  Class description
SystemException  Basic classes of exceptions that other users can handle
ArgumentException  Method parameters are illegal
ArgumentNullException  An empty parameter is passed to the method , This method cannot accept this parameter
ArgumentOutOfRangeException  Parameter value is out of range
ArithmeticException  Arithmetic overflow or underflow occurs
ArrayTypeMismatchException  Trying to store an object of the wrong type in an array
BadImageFormatException  The graphics are in the wrong format
DivideByZeroException  Abnormal division by zero
DllNotFoundException  The referenced DLL
FormatException  Parameter format error
IndexOutOfRangeException  Array index out of range
InvalidCastException  Use invalid class
InvalidOperationException  Method call time error
MethodAccessException  Try to visit Siyou or protected methods
MissingMemberException  Access an invalid version of DLL
NotFiniteNumberException  Object is not a valid member
NotSupportedException  The method called is not implemented in the class
NullReferenceException  Trying to use an unassigned reference
OutOfMemoryException  Not enough memory
PlatformNotSupportedException  This error is thrown when the platform does not support a specific property
StackOverflowException  stack overflow
Exception： Base class for all exception objects .
SystemException： Base class for all errors generated at runtime .
IndexOutOfRangeException： When the subscript of an array is out of range, the runtime raises .
NullReferenceException： Raised by the runtime when an empty object is referenced .
InvalidOperationException： When the call to a method is invalid for the current state of the object , Caused by certain methods .
ArgumentException： Base class for all parameter exceptions .
ArgumentNullException： When the parameter is empty （ Don't allow ） Under the circumstances , Raised by method .
ArgumentOutOfRangeException： When the parameter is not within a given range , Raised by method .
InteropException： The goal is or occurs in CLR The base class of exceptions in the external environment .
ComException： contain COM Class HRESULT Abnormal information .
SEHException： encapsulation Win32 Structural exception handling information exception .
SqlException： Encapsulates the SQL Abnormal operation .


2.2  Custom exception

in application , If the exception class provided by the system cannot meet the requirements , We can customize exceptions by ourselves , You can create exception classes by yourself .

 class outException : ApplicationException// Our custom exception class inherits Exception The derived class ApplicationException To complete
 {
 string str;
 public outException():base()// Define the constructor
 {
 this.str = " We don't accept 1 This number is the divisor ,IC00 Yes ！";
 
 }
 public override string ToString()// Rewrite Tostring
 {
 return str.ToString();
 }
 }


summary

Debugging is an important step and means of writing programs , Exception handling is to avoid application errors , It is a firewall to prevent program errors . Debugging is an essential skill when we write programs , It can make our program query and correct errors faster , Convenient for our program development , Learning this skill can help us develop high-quality programs , Okay , Creation is not easy to like, pay attention to comment collection ！！！ Praise Oh ....