C Error Trapping
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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
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functions. For example, -1 and NULL are used in several functions error trapping excel vba such as socket() (Unix socket programming) or malloc() respectively to indicate problems that the programmer should be
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aware about. In a worst case scenario where there is an unavoidable error and no way to recover from it, a C programmer usually tries to log the error error trapping java and "gracefully" terminate the program. There is an external variable called "errno", accessible by the programs after including
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Questions Jobs Documentation Tags Users 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 https://en.wikibooks.org/wiki/C_Programming/Error_handling other. Join them; it only takes a 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 http://stackoverflow.com/questions/385975/error-handling-in-c-code would look like this: MYAPI_ERROR getObjectSize(MYAPIHandle h, int* returnedSize); The 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
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 http://www.on-time.com/ddj0011.htm design of RTFiles, the embedded filesystem component of On Time RTOS-32, our Win32-compatible RTOS http://en.cppreference.com/w/cpp/error for 32-bit x86 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 error trapping this problem is return codes. 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 error trapping java hierarchy up to about 15 levels deep, 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 allocat
Containers library Algorithms library Iterators library Numerics library Input/output library Localizations library Regular expressions library (C++11) Atomic operations library (C++11) Thread support library (C++11) Filesystem library (C++17) Technical Specifications [edit] Utilities library Type support (basic types, RTTI, type traits) Dynamic memory management Error handling Program utilities Variadic functions Date and time Function objects initializer_list(C++11) bitset hash(C++11) Relational operators rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>= optional, any and variant (C++17) optional any variant in_placein_place_tin_place_type_tin_place_index_t Pairs and tuples pair tuple(C++11) apply(C++17) make_from_tuple(C++17) piecewise_construct_t(C++11) piecewise_construct(C++11) integer_sequence(C++14) Swap, forward and move swap exchange(C++14) forward(C++11) move(C++11) move_if_noexcept(C++11) Type operations declval(C++11) as_const(C++17) [edit] Error handling Exception handling exception uncaught_exceptionuncaught_exceptions(C++17) exception_ptr(C++11) make_exception_ptr(C++11) current_exception(C++11) rethrow_exception(C++11) nested_exception(C++11) throw_with_nested(C++11) rethrow_if_nested(C++11) Exception handling failures terminate terminate_handler get_terminate(C++11) set_terminate unexpected(deprecated) bad_exception unexpected_handler(deprecated) get_unexpected(C++11)(deprecated) set_unexpected(deprecated) Exception categories logic_error invalid_argument domain_error length_error out_of_range runtime_error range_error overflow_error underflow_error tx_exception(TM TS) Error codes Error codes errno Assertions assert system_error facility error_category(C++11) generic_category(C++11) system_category(C++11) error_condition(C++11) errc(C++11) error_code(C++11) system_error(C++11) [edit] Contents 1 Exception handling 1.1 Capture and storage of exception objects 1.2 Handling of failures in exception handling 1.3 Handling of exception specification violations 1.