How To Print Error Message In C
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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
C Error Handling Best Practices
to the name of the program that encountered the error. Function: char c error codes * strerror (int errnum) Preliminary: | MT-Unsafe race:strerror | AS-Unsafe heap i18n | AC-Unsafe mem | See POSIX Safety Concepts.
Error.h C
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. c programming error codes 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 c stderr | 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
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Error Handling In C++
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Print To Stderr C
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 http://www.gnu.org/s/libc/manual/html_node/Error-Messages.html other. Join them; it only takes a minute: Sign up Error checking fprintf when printing to stderr up vote 8 down vote favorite 3 According to the docs, fprintf can fail and will return a negative number on failure. There are clearly many situations where it would be useful to check this value. However, I usually use fprintf http://stackoverflow.com/questions/4846562/error-checking-fprintf-when-printing-to-stderr to print error messages to stderr. My code will usually look something like this: rc = foo(); if(rc) { fprintf(stderr, "An error occured\n"); //Sometimes stuff will need to be cleaned up here return 1; } In these cases, is it still possible for fprintf to fail? If so, is there anything that can be done to display the error message somehow or is there is a more reliable alternative to fprintf? If not, is there any need to check fprintf when it is used in this way? c share|improve this question asked Jan 31 '11 at 0:18 Rupert Madden-Abbott 5,988104055 add a comment| 5 Answers 5 active oldest votes up vote 11 down vote accepted The C standard says that the file streams stdin, stdout, and stderr shall be connected somewhere, but they don't specify where, of course. It is perfectly feasible to run a program with them redirected: some_program_of_yours >/dev/null 2>&1
there are ways to do error handling. Of course the programmer needs to prevent errors during coding and should always test the return values https://www.codingunit.com/c-tutorial-error-handling-exception-handling of functions called by the program. A lot of C function calls return a -1 or NULL in case of an error, so quick test on these return values are 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 operating in c 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 need to how to print 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