Delphi – Is there a general E-unfailed exception: exception?

try
 i := StrToInt(s);
 {...do a lot more...}
 except
 on E: EConvertError do begin
 ShowMessage('You need to input a valid number.');
 end;
 on E: Exception do begin
 ShowMessage('Something went wrong.'); 
 Raise; 
 end;
 end;

try
 i := StrToInt(s);
 {...do a lot more.. .}
 except
 on E: EConvertError do begin
 ShowMessage('You need to input a valid number.');
 end;
 else begin // swapped on e: Exception with else
 ShowMessage('Something went wrong.');
 Raise; 
 end;
 end;

try
 ....
except 
 // deal with all exceptions
end;

if TryStrToInt(s, i) then
 // do stuff with i
else
 // deal with conversion error

I want to know if there are exceptions/errors, which will cause your code to jump to an except block but will not be processed by the E: exception.

try
 i := StrToInt(s);
 {...do a lot more...}
 except
 on E: EConvertError do begin
 ShowMessage('You need to input a valid number.');
 end;
 on E: Exception do begin
 ShowMessage('Something went wrong.'); 
 Raise; 
 end;
 end;

Is there a way to make a program erroneously ignore the two statements other than the block?
Or should I do this:

try
 i := StrToInt(s);
 {...do a lot more.. .}
 except
 on E: EConvertError do begin
 ShowMessage('You need to input a valid number.');
 end;
 else begin // swapped on e: Exception with else
 ShowMessage('Something went wrong.');
 Raise; 
 end;
 end;

< /p>

You can throw anything derived from TObject. In order to capture each such class, you need to specify TObject in the on statement.

From the documentation:

Exception types are declared just like other classes. In fact, it is possible to use an instance of any class as an exception, but it is recommended that exceptions be derived from the SysUtils.Exception class defined in SysUtils.

Actually, I know that there is no code that can throw anything that is not derived from Exception, although @TLama pointed out in the comments that the old version is deprecated An example in the VCL class. Of course StrToInt will only throw Exception descendants.

If you don’t need to access the exception object, you can use the plain except clause instead of the on statement.

try
 ....
except 
 // deal with all exceptions
end;

Or you can use on Els of the statement The e clause serves as catch all, and again you will not access the exception object immediately.

Otherwise, you can specify the base class for the exception to be caught. For example, E: TObject captures all content derived from TObject.< /p>

So, as we have seen, something that is not derived from Exception may be thrown. But you have to ask yourself, has your code ever done this? If not, then it makes the most sense to test the Exception in a catch catch all handler. This will give you access to the members of the Exception. Of course, people do want to know why you have a catch all exception handler. Their presence often indicates the design Poor.

Continuing the topic of StrToInt, you only need to catch EConvertError. This is the problem that is raised when the conversion fails. You should ignore any other exception classes, because in your example, the code will not know how Handle any other exceptions. One of the goals of writing exception handling code is to handle the content you know how to handle, and ignore everything else.

In fact, TryStrToInt is what you need:

if TryStrToInt(s, i) then
 // do stuff with i
else
 // deal with conversion error

This eliminates It eliminates the need to handle any exceptions and makes your code more readable.

I know StrToInt is just an example, but it is a good demonstration of the benefits of trying to avoid exceptions.