C Print To Error Stream
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templates, inheritance, etc. new and delete the stream operators << >> the // comment character the bool keyword all those weird casting operators (dynamic_cast, static_cast) the standard libraries you're used to (e.g. iostream) lots python print to error stream of other stuff We'll cover some of the basics here. I've also written up some c print standard error linked list code both in C++ and C to give you a sense of the differences. The end of this document has a c print stdout couple of recommended books where you can go for further information (including classic book on C written by Kernighan and Ritchie and referred to here as K&R). The man pages are also a great source of information. Comments print to stderr c The only valid way to specify a comment in C is like so: /* this is a comment */ /* This is a multiline comment */ You cannot nest comments. /* This is /*nested */ comment. And is illegal. */ I/O C doesn't have stream operators. Instead you'll want to use the functions provided in the stdio library. In particular: printf, fprintf, fgets, fputs. Output: printf, fprintf, fputs The most common output function in C is
Fprintf Stderr C
printf() which prints characters to the screen (or wherever standard out is directed to go). Here's a quick hello world program that illustrates its use: #include
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Print To Stderr Bash
workings and policies of this site About Us Learn more about Stack stderr c example Overflow the company Business Learn more about hiring developers or posting ads with us Stack Overflow Questions Jobs print to stderr perl 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 other. Join http://people.cs.uchicago.edu/~iancooke/osstuff/ccc.html them; it only takes a minute: Sign up When should I use perror(“…”) and fprintf(stderr, “…”)? up vote 54 down vote favorite 24 Reading the man pages and some code did not really help me in understanding the difference between - or better, when I should use - perror("...") or fprintf(stderr, "..."). c stderr share|improve this question edited Jan http://stackoverflow.com/questions/12102332/when-should-i-use-perror-and-fprintfstderr 11 at 22:36 Jamal 56061625 asked Aug 24 '12 at 2:03 freeboy1015 6771612 add a comment| 4 Answers 4 active oldest votes up vote 56 down vote accepted Calling perror will give you the interpreted value of errno, which is a thread-local error value written to by POSIX syscalls (i.e., every thread has it's own value for errno). For instance, if you made a call to open(), and there was an error generated (i.e., it returned -1), you could then call perror immediately afterwards to see what the actual error was. Keep in mind that if you call other syscalls in the meantime, then the value in errno will be written over, and calling perror won't be of any use in diagnosing your issue if an error was generated by an earlier syscall. fprintf(stderr, ...) on the other-hand can be used to print your own custom error messages. By printing to stderr, you avoid your error reporting output being mixed with "normal" output that should be going to stdout. Keep in mind that fprintf(stderr, "%s\n", strerror(errno))
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 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 print 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 print to stderr 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-Uns