Error Handling Function In C
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the company Business Learn more about hiring developers or posting ads with us Stack Overflow Questions Jobs Documentation php error handling function 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 other. Join them; vbscript error handling function 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 would look like this: MYAPI_ERROR
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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 not involving exceptions since it's not an option for me a
there are ways to do error handling. Of course the programmer needs to prevent errors during coding and should always test the return file handling function in c values of functions called by the program. A lot of C function calls string handling function in c return a -1 or NULL in case of an error, so quick test on these return values are
C Error Handling Best Practices
easily done with for instance an ‘if statement’. In previous tutorials we already mention that this behavior (returning numbers to indicate an error) is also used in Unix or Linux like http://stackoverflow.com/questions/385975/error-handling-in-c-code operating systems. For instance if a program successful ends the return value of the program is zero. If the program ends with an error usually a number larger than zero is returned (for example 1). (With command ‘echo $?’ on the command line you can display the return code of a program that has previously run). So the one thing you https://www.codingunit.com/c-tutorial-error-handling-exception-handling need to remember is that you (the programmer) are responsible for error handling. You’re the person that needs to make sure that a program will gracefully terminate and not just CRASH unexpectedly! It is you that need to take appropriate action depending on the return values of function calls. Global Variable errno The global variable errno is used by C functions and this integer is set if there is an error during the function call. To make use of errno you need to include errno.h and you need to call ‘extern int errno;’ Let us take a look at an example: #include
of a library call. The functions strerror and perror give you the standard error message for a given error code; the http://www.gnu.org/s/libc/manual/html_node/Error-Messages.html 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 https://news.ycombinator.com/item?id=3883310 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 handling 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 error handling function 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 lo
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 get the job done in the cleanest possible way, so you should use them for 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 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 1631 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() { 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 1631 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 1631 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 is not the case. Also, that code is not portable since NULL does not have to be 0. cdellin 1631 days ago Just a correction: the code is actually perfectly portable. The integer constant 0 is the canonical definition of the null point