C Error Handling
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C - Basic Syntax C - Data Types C - Variables C - Constants C - Storage Classes C - Operators C - Decision Making C - Loops C - Functions C - Scope Rules C - Arrays C - Pointers C - Strings c error handling best practices C - Structures C - Unions C - Bit Fields C - Typedef C - Input &
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Output C - File I/O C - Preprocessors C - Header Files C - Type Casting C - Error Handling C - Recursion C objective c error handling - Variable Arguments C - Memory Management C - Command Line Arguments C Programming Resources C - Questions & Answers C - Quick Guide C - Useful Resources C - Discussion Selected Reading Developer's Best Practices Questions and Answers Effective Resume c error handling goto Writing HR Interview Questions Computer Glossary Who is Who C - Error Handling Advertisements Previous Page Next Page As such, C programming does not provide direct support for error handling but being a system programming language, it provides you access at lower level in the form of return values. Most of the C or even Unix function calls return -1 or NULL in case of any error and set an error code errno. It is set as a global variable
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and indicates an error occurred during any function call. You can find various error codes defined in
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 in several functions such as socket() (Unix socket programming) c coding style error handling or malloc() respectively to indicate problems that the programmer should be aware about. In c sharp error handling a worst case scenario where there is an unavoidable error and no way to recover from it, a C programmer usually tries to
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log the error and "gracefully" terminate the program. There is an external variable called "errno", accessible by the programs after including
single target inside a function) is just perfect for C error handling code. Don't be misguided by a silly principle of goto's being always bad. They https://news.ycombinator.com/item?id=3883310 get the job done in the cleanest possible way, so you should use them for http://www.gnu.org/s/libc/manual/html_node/Error-Messages.html doing cleanups.The examples did not have any resources to clean up, and that is what makes error handling in C painful. In the absence of any cleanup routines, this will do: return ( do_something() == SUCCESS && do_something_else() == SUCCESS && do_final_thing() == SUCCESS) ? SUCCESS : FAILURE; Of course, once you add resources to clean up error handling or error codes that are meaningful (not just success/fail) error handling gets more painful.You should not try to perfect something as mundane as error handling. Just write the damn code and get over it. tspiteri 1624 days ago Why should the goto be to one single target? Multiple goto statements are good for multiple clean ups without adding indentation levels and without having artificially long logic ands. For example: int init_abc() { c error handling if (!init_a()) goto err_a; if (!init_b()) goto err_b; if (!init_c()) goto err_c; return 1; err_c: cleanup_b(); err_b: cleanup_a(); err_a: return 0; } seems to be the cleanest way to do what it does in C. For what it's worth, it is the way a lot of error handling is done in the Linux kernel. exDM69 1624 days ago I guess it's fine to use multiple targets too. However, usually you can get away with one, because free(NULL) and similar cleanups tend to be no-ops. So you have something like: char *foo = 0, *bar = 0; if((foo = malloc(X)) == NULL || (bar = malloc(Y)) == NULL) goto cleanup; make_me_millions(foo, bar); cleanup: free(bar); free(foo); In this case, and many cases like it, there's no need to have two jump targets, because one is good enough. You'll have to declare the variables early on anyway to avoid warnings/errors from definitions that cross jump labels.So there's probably nothing wrong with multiple jump targets but that might not be needed with well-behaving cleanup functions. adestefan 1624 days ago because free(NULL) and similar cleanups tend to be no-ops. So you have something likeYou really need to check the specification on each function. free is defined that free(NULL) is no-op, but there are other things where that
of a library call. The functions strerror and perror give you the standard error message for a given error code; the variable program_invocation_short_name gives you convenient access to the name of the program that encountered the error. Function: char * strerror (int errnum) Preliminary: | MT-Unsafe race:strerror | AS-Unsafe heap i18n | AC-Unsafe mem | See POSIX Safety Concepts. The strerror function maps the error code (see Checking for Errors) specified by the errnum argument to a descriptive error message string. The return value is a pointer to this string. The value errnum normally comes from the variable errno. You should not modify the string returned by strerror. Also, if you make subsequent calls to strerror, the string might be overwritten. (But it’s guaranteed that no library function ever calls strerror behind your back.) The function strerror is declared in string.h. Function: char * strerror_r (int errnum, char *buf, size_t n) Preliminary: | MT-Safe | AS-Unsafe i18n | AC-Unsafe | See POSIX Safety Concepts. The strerror_r function works like strerror but instead of returning the error message in a statically allocated buffer shared by all threads in the process, it returns a private copy for the thread. This might be either some permanent global data or a message string in the user supplied buffer starting at buf with the length of n bytes. At most n characters are written (including the NUL byte) so it is up to the user to select a buffer large enough. This function should always be used in multi-threaded programs since there is no way to guarantee the string returned by strerror really belongs to the last call of the current thread. The function strerror_r is a GNU extension and it is declared in string.h. Function: void perror (const char *message) Preliminary: | MT-Safe race:stderr | AS-Unsafe corrupt i18n heap lock | AC-Unsafe corrupt lock mem fd | See POSIX Safety Concepts. This function prints an error message to the stream stderr; see Standard Streams. The orientation of stderr is not changed. If you call perror with a message that is either a null pointer or an empty string, perror just prints the error message corresponding to errno, adding a trailing newline. If you supply a non-