Fprintf Error Checking
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C Error Handling
Developer's Best Practices Questions and Answers Effective Resume 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 error handling in c++ an error code errno. It is set as a global variable and indicates an error occurred during any function call. You can find various error codes defined in
Question Need help? Post your question and get tips & solutions from a community of 418,551 IT Pros & Developers. It's quick & easy. Checking fprintf for errors and testing for existence of a file P: n/a Jim Hunter From
C Error Codes
what I've read, the only indication fprintf gives of an error is a negative return value.
C Error Handling Best Practices
I have a series of writes to a file using fprintf, and, while I need to know if a failure has occurred, I don't particularly exception handling in c sharp care which call failed - just that one of them did. I was thinking I might simply check the return value of the last call to fprintf. Is it reasonable to assume that if one call to fprintf fails, then all https://www.tutorialspoint.com/cprogramming/c_error_handling.htm subsequent calls will fail? Or should I check (shudder) after every call? Secondly, what's the best way to portably determine whether a file exists? The only way I can see to do it is to attempt to open it for reading, and see if that fails, but then you still aren't guaranteed that the file doesn't exist. Thanks in advance. Jim Nov 14 '05 #1 Post Reply Share this Question 3 Replies P: n/a Mark McIntyre On 06 Mar 2005 01:08:17 -0600, in https://bytes.com/topic/c/answers/220724-checking-fprintf-errors-testing-existence-file comp.lang.c , Jim Hunter
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 http://www.gnu.org/s/libc/manual/html_node/Error-Messages.html the program that encountered the error. Function: char * strerror (int errnum) Preliminary: | http://www.cplusplus.com/reference/cstdio/fprintf/ 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 c error 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 c error handling 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-nul
beginning with %), the additional arguments following format are formatted and inserted in the resulting string replacing their respective specifiers. After the format parameter, the function expects at least as many additional arguments as specified by format. Parameters stream Pointer to a FILE object that identifies an output stream. format C string that contains the text to be written to the stream. It can optionally contain embedded format specifiers that are replaced by the values specified in subsequent additional arguments and formatted as requested. A format specifier follows this prototype: %[flags][width][.precision][length]specifier Where the specifier character at the end is the most significant component, since it defines the type and the interpretation of its corresponding argument: specifierOutputExample d or iSigned decimal integer392 uUnsigned decimal integer7235 oUnsigned octal610 xUnsigned hexadecimal integer7fa XUnsigned hexadecimal integer (uppercase)7FA fDecimal floating point, lowercase392.65 FDecimal floating point, uppercase392.65 eScientific notation (mantissa/exponent), lowercase3.9265e+2 EScientific notation (mantissa/exponent), uppercase3.9265E+2 gUse the shortest representation: %e or %f392.65 GUse the shortest representation: %E or %F392.65 aHexadecimal floating point, lowercase-0xc.90fep-2 AHexadecimal floating point, uppercase-0XC.90FEP-2 cCharactera sString of characterssample pPointer addressb8000000 nNothing printed. The corresponding argument must be a pointer to a signed int. The number of characters written so far is stored in the pointed location. %A % followed by another % character will write a single % to the stream.% The format specifier can also contain sub-specifiers: flags, width, .precision and modifiers (in that order), which are