does file related functions throw an exception when it fails OR just return false.
Coz even if I use it in try-catch, there is no point in catching an exception if fopen/fwrite does not throw it at all…
Return Values
Returns a file pointer resource on success, or FALSE on error.
Errors/Exceptions
If the open fails, an error of level E_WARNING is generated. You may use # to suppress this warning.
Check documentation. you can throw custom exception if you want to.
Related
I notices some code that made me think the Exception function call was optional? E.g., do these two lines perform the same function?
throw Exception('oops!');
throw 'oops!'
No.
The former, throw Exception('oops!');, creates a new Exception object using the Exception constructor, then throws that object.
It can be caught by try { ... } on Exception catch (e) { ... }.
The latter, throw 'oops!'; throws the string object.
It can be caught by try { ... } on String catch (e) { ... }.
Generally, you shouldn't be doing either.
If someone made an error, something that would have been nice to catch at compile-time and reject the program, but which happens to not be that easy to detect, throw an Error (preferably some suitable subclass of Error).
Errors are not intended to be caught, but to make the program fail visibly. Some frameworks do catch errors and log them instead. They're typically able to restart the code which failed and carry on, without needing to understand why.
If your code hit some exceptional situation which the caller should be made aware of (and which prevents just continuing), throw a specific subclass of Exception, one which contains the information the caller needs to programmatically handle that situation. Document that the code throws this particular exception. It's really a different kind of return value more than it's an error report. Exceptions are intended to be caught and handled. Not handling an exception is, itself, an error (which is why it's OK for an uncaught exception to also make the program fail visibly).
If you're debugging, by all means throw "WAT!"; all you want. Just remove it before you release the code.
I am using CTFontManagerRegisterGraphicsFont to register CGFont loaded at runtime from various sources (files, memory, ..), but some fonts raises an Exception with the following message:
Exception: "*** -[__NSPlaceholderArray initWithObjects:count:]: attempt to insert nil object from objects[0]"
an alternative to CTFontManagerRegisterGraphicsFont is CTFontManagerRegisterFontsForURL:
using this function I did not have any exception raised.
My Questions:
What is the cause of this behavior difference
How to catch & discard the exception raised by CTFontManagerRegisterGraphicsFont
Is there any thing to be done before calling CTFontManagerRegisterGraphicsFont to prevent the exception.
What .persistent scope mean for 2nd parameter in CTFontManagerRegisterFontsForURL.
I'm using Error Handling in WorkFusion.
Is there a way to see the error message in the catch block i.e. exception occurred block.
How about using:
<log>exception_msg_var</log>
or
println exception_msg_var
exporting exceptions to datastore?
To get the error message in RPA Express, you can keep the code outside of exception handling and then, the software will through error message on its' own. Once you get the type of error (by running the bot once), you can put the solution in catch block by keeping the code inside exceptional handling feature.
I have an iOS application written in Swift 2 in Xcode 8.2.1, that's built for iOS 10.2.
I've had a number of crash reports from TestFlight and despite symbolication, none of the crash logs show any program state besides the stack-traces (no argument values, no locals, no heap objects, etc).
...but inside those functions I can see code which is likely to fail (e.g. a forced unwrap) but the crash log isn't telling me where or why it's failing.
When debugging in Xcode, I can use fatalError(message: String) where I can put my own message like "functionFoo returned nil" or "variable bar == \"" + bar + "\"", except when deployed using TestFlight or the App Store the fatalError will be hit and the program terminates, but the message value is not saved to the crash log, making it pointless.
In other environments, like C#/.NET and Java I can simply throw new SomeExceptionType("my message") and all information is available in whatever global catch(Exception) handler I have.
How can I achieve the same goal in iOS / Swift?
Swift does support error handling. You can create your own error type by confirming to Error protocol or use existing error types and then throw an error by invoking throw error.
But Swift forces you add error handling to any code that can throw an error. There are multiple way you can handle error in swift.
Apply throws keyword to your function, this indicates that the function can throw an error when invoked and the error should be handled by the caller.
func canThrowErrors() throws -> String
When invoking methods with throws keyword you have to add try keyword at the beginning of the invocation. All these try invocations should be handled either by applying throws to method to just propagate the errors or wrapping inside a do-catch block:
do {
try canThrowErrors()
try canThrowOtherErrors()
} catch is SpecificError {
// handling only specific error type
} catch let error as SpecificError {
// catches only specific error for type
} catch {
// catches all errors
}
Additionally you can use try? and try! for throwing function invocation to disable error propagation and retrieve optional result that returns nil in case of error and runtime assertions respectively.
By forcing you to handle all the errors at compile time swift avoids any undefined runtime behavior and debugging nightmare.
I would suggest to use fatalError or any other runtime assertion only if scenarios when there is no way to recover from a state without crashing the app. Unfortunately, there is no way to handle errors from fatalError as its use is only reserved for such scenarios only. Also, in your crashlog you will only get the line number that caused the crash to get additional info for the cause of crash I would suggest to use custom logging or analytics.
I have a project that runs perfect under windows xp.
Now I have tried to run it under Windows 7 and got there a lot of exceptions under Immediate window.
A first chance exception of type 'System.ArgumentNullException' occurred in Microsoft.VisualBasic.dll
A first chance exception of type 'System.IO.FileNotFoundException' occurred in LP_Wizard.exe
A first chance exception of type 'System.ArgumentException' occurred in LP_Wizard.exe
A first chance exception of type 'System.NullReferenceException' occurred in LP_Wizard.exe
A first chance exception of type 'System.InvalidCastException' occurred in Microsoft.VisualBasic.dll
A first chance exception of type 'System.ArgumentNullException' occurred in Microsoft.VisualBasic.dll
A first chance exception of type 'System.IO.FileNotFoundException' occurred in LP_Wizard.exe
A first chance exception of type 'System.InvalidCastException' occurred in Microsoft.VisualBasic.dll
A first chance exception of type 'System.ArgumentNullException' occurred in Microsoft.VisualBasic.dll
A first chance exception of type 'System.IO.FileNotFoundException' occurred in LP_Wizard.exe
A first chance exception of type 'System.ArgumentNullException' occurred in Microsoft.VisualBasic.dll
A first chance exception of type 'System.IO.FileNotFoundException' occurred in LP_Wizard.exe
Any idea what wrong with that Microsoft.VisualBasic.dll in windows 7 and how i correct that problem ?
Thanks a lot for help .
If you want to pinpoint where the exceptions are occurring, you can select the Debug->Exceptions menu item, and in the dialog that appears, check the first checkbox for "Common Language Runtime Exceptions". This will make the debugger break as soon as an exception occurs instead of only breaking on unhandled exceptions.
This is also one reason why it is generally a bad idea to catch generic exceptions unless you are clearly logging the information caught.
What is happening is the debugger can "see" exceptions as soon as they are raised (hence the "first chance") before any catch block is hit. Any exception which is not handled by a catch block is considered a "second chance" exception and will break normally.
If these exceptions aren't stopping the running of your application because they are unhandled then you are probably OK. Most of the time the exception is handled by code and this isn't a problem. The output is simply Visual Studio letting you know the exceptions were raised.
See the "Avoiding first chance exception messages when the exception is safely handled" question for some methods to reduce this if there are too many to ignore.
Are your in the debugger? Are these exceptions your program is handling? If so you need to find a setting that tells VB to supress warning you of handled exceptions. Maybey this was set when installed on XP but not when you installed on W7. See if this helps:
http://www.helixoft.com/blog/archives/24