Error Trapping In C
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known as exception handling). By convention, the programmer is expected to prevent errors from occurring in the first place, and test return values from functions. For example, -1 and NULL are used php error trapping in several functions such as socket() (Unix socket programming) or malloc() respectively to
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indicate problems that the programmer should be aware about. In a worst case scenario where there is an unavoidable error trapping powershell error and no way to recover from it, a C programmer usually tries to log the error and "gracefully" terminate the program. There is an external variable called "errno", accessible by the programs error trapping java after including
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allocation completed properly: #include
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Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 4.7 million programmers, just like you, helping each other. Join them; it only takes a https://en.wikibooks.org/wiki/C_Programming/Error_handling minute: Sign up Error handling in C code up vote 102 down vote favorite 59 What do you consider "best practice" when it comes to error handling errors in a consistent way in a C library. There are two ways I've been thinking of: Always return error code. A typical function would look like this: MYAPI_ERROR getObjectSize(MYAPIHandle h, int* returnedSize); The http://stackoverflow.com/questions/385975/error-handling-in-c-code always provide an error pointer approach: int getObjectSize(MYAPIHandle h, MYAPI_ERROR* returnedError); When using the first approach it's possible to write code like this where the error handling check is directly placed on the function call: int size; if(getObjectSize(h, &size) != MYAPI_SUCCESS) { // Error handling } Which looks better than the error handling code here. MYAPIError error; int size; size = getObjectSize(h, &error); if(error != MYAPI_SUCCESS) { // Error handling } However, I think using the return value for returning data makes the code more readable, It's obvious that something was written to the size variable in the second example. Do you have any ideas on why I should prefer any of those approaches or perhaps mix them or use something else? I'm not a fan of global error states since it tends to make multi threaded use of the library way more painful. EDIT: C++ specific ideas on this would also be interesting to hear about as long as they are not involving exceptions since it's not an option for me at the moment... c error-handling share|improve this question edited Nov 6
Peter Petersen Error handling is an important issue in embedded systems, and it can account for a substantial portion of a project's code. We were faced with this issue during the design of http://www.on-time.com/ddj0011.htm RTFiles, the embedded filesystem component of On Time RTOS-32, our Win32-compatible RTOS for 32-bit x86 http://rlc.vlinder.ca/blog/2010/01/error-handling-in-c/ targets. The core filesystem is portable with a C function API to the application and a device-driver interface below it. Typically, errors can occur in device drivers and must be reported to the application with suitable return codes, so errors must travel through the complete core filesystem. The classic C approach to this problem is return codes. error trapping Each function returns a value indicating success or failure. However, with a nontrivial function call hierarchy, this approach clutters the code significantly. Every function must check the return code of every function call it makes and take care of errors. In most cases, the function will merely pass any errors back up to its caller. RTFiles has several hundred internal functions and a call hierarchy up to about 15 levels deep, error trapping in so this approach would have been a nightmare to maintain. Programming languages such as Ada or C++ address this issue with exceptions. Exceptions make it easy to separate error handling from the rest of the code. Intermediate functions can completely ignore errors occurring in functions they call, if they can't handle them anyway. Exceptions are much easier to maintain than error return codes, so we definitely wanted to use them for RTFiles. Unfortunately, we had to write RTFiles in C, and not C++ or Ada, for portability. RTFiles must support compilers without C++ support. Another issue is overhead and reliability. C++ exception handling needs a lot of run-time system support routines, which might add too much code to a small embedded system. C++ exceptions are objects dynamically allocated from the heap, but many embedded systems do not want to use any dynamic memory allocation to avoid heap fragmentation and out-of-heap-space problems. For example, what would happen if an RTFiles device driver throws a disk-write-protection exception, and the heap allocation called by throw throws an out-of-memory exception? The solution to the problem is to implement a simple exception-handling library in C with the following goals: No dynamic memory allocation. Robust (the exception handling library itself must not fail). Must support both exception-handlers and finally-han
handling in C Posted on January 16, 2010 by rlc One of the things I do as a analyst-programmer is write software - that would be the "programmer" part. I usually do that in C++ but, sometimes, when the facilities of C++ aren't available (e.g. no exception handling and no RTTI) C becomes a more obvious choice. When that happens, RTTI is not the thing I miss the most - you can get around that using magic numbers if you need to. Exceptions, on the other hand, become a very painful absence when you're used to using them. Error handling is a very important part of programming: a lot of things can go wrong when a program runs and most of those things need to be handled properly because the functionalities of your program depend on them. C++ uses exceptions for this purpose, so that if a call to foo fails, you don't have to handle that failure in the context of your call - especially if you wouldn't be able to do anything about it anyway. Thus, the following code: foo(); bar(); will call bar only if foo didn't throw any exceptions. Presumably both do something useful and neither of them return anything useful. Now, the same thing would be true in C if we did something like this: int result = foo(); if (result == 0) result = bar(); Now, both foo and bar return a result code which, in this case, is 0 if all is well. Windows programmers will be more familiar with this: HRESULT result = foo(); if (SUCCEEDED(result)) result = bar(); which amounts to the same thing. HRESULT, after all, is a 32-bit unsigned integer of which a few bits are reserved to indicate where the error originated and the other bits indicate the error. An HRESULT value of 0 means no error, so the SUCCEEDED basically checks whether the result is 0. The trouble starts when the function returned an integer already - e.g. a getFooCount function: unsigned int foo_count(getFooCount()); foo(foo_count); In this code, foo only gets called when getFooCount returns a valid value - which