Ofstream Error Handling
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Ofstream Fail
up Error handling in std::ofstream while writing data up vote 1 down vote favorite I have a small program where i initialize a string and write to a file stream: #include
Ofstream Open Error
how are you"; if(ofs) ofs< does not encounter the above issue, hence I am unable to know why it failed. Please tell me, by which other options I would be able to know that "ofs< has failed. Thanks in advance. c++ ofstream share|improve this question asked Feb 5 '15 at 11:23 Santosh ofstream example Sahu 79821126 Have you checked that the ofstream is actually open before trying to ofs < –tuple_cat Feb 5 '15 at 11:25 @zenith: Edited it –Santosh Sahu Feb 5 '15 at 11:27 ofstream::operator<< will modify the internal state flags if it fails. Have you checked ofstream::eof/bad/fail? –tuple_cat Feb 5 '15 at 11:31 @zenith: internal state flags will change if it fails to open the file. can you confirm if it fails while writing also? Request you to please show some cod e if possible. –Santosh Sahu Feb 5 '15 at 11:36 Check the Return value section here. Does that answer your question? –tuple_cat Feb 5 '15 at 11:45 | show 4 more comments 2 Answers 2 active oldest votes up vote 4 down vote In principle, if there is a write error, badbit should be set. The error will only be set when the stream actually tries to write, however, so because of buffering, it may be set on a later write than when the error occurs, or even after close. And the bit is “sticky”, so once set, it will stay set. Given the above, the usual procedure is to just verify the status of the output after close; when outputting to std::cout or std::cerr, after the final flush. Something like: std::ofstream f(...); // all sorts of output (usually to the `std::ostream&` in a // function). f.close(); if ( ! f ) { // Error handling. Most i
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Std Ofstream Write
ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the c++ ifstream open fail Stack Overflow Community Stack Overflow is a community of 6.2 million programmers, just like you, helping each other. Join them; it only takes a fstream write error minute: Sign up How to get error message when ifstream open fails up vote 39 down vote favorite 7 ifstream f; f.open(fileName); if ( f.fail() ) { // I need error message here, like "File not found" etc. - // the http://stackoverflow.com/questions/28342660/error-handling-in-stdofstream-while-writing-data reason of the failure } How to get error message as string? c++ error-handling stream std share|improve this question edited Mar 7 '14 at 2:28 lpapp 35.4k134766 asked Jun 27 '13 at 7:51 0123456789 24.2k2191157 2 possible duplicate of C++ ifstream Error Checking –Matthieu Rouget Jun 27 '13 at 8:19 1 possible duplicate of Can you get a specific error condition when a C++ stream open fails? –arne Jun 27 '13 at 8:28 3 @Alex Farber: Sure. cerr << "Error http://stackoverflow.com/questions/17337602/how-to-get-error-message-when-ifstream-open-fails code: " << strerror(errno); // Get some info as to why seems relevant to the question. –Matthieu Rouget Jun 27 '13 at 8:28 @MatthieuRouget: Check the possible duplicate I posted -- it seems this is non-standard behaviour only implemented by gcc. –arne Jun 27 '13 at 8:29 @MatthieuRouget: strerror(errno) works. Post this as answer, I will accept it. –0123456789 Jun 27 '13 at 8:37 add a comment| 3 Answers 3 active oldest votes up vote 30 down vote accepted Every system call that fails update the errno value. Thus, you can have more information about what happens when a ifstream open fails by using something like : cerr << "Error: " << strerror(errno); However, since every system call updates the global errno value, you may have issues in a multithreaded application, if another system call triggers an error between the execution of the f.open and use of errno. Edit (thanks to Arne Mertz and other people in the comments): e.what() seemed at first to be a more C++-idiomatically correct way of implementing this, however the string returned by this function is implementation-dependant and (at least in G++'s libstdc++) this function useful information about the reason behind the error... share|improve this answer edited Jun 27 '13 at 11:53 answered Jun 27 '13 at 9:02 Matthieu Rouget 2,026720 1 e.what() does not seem to give much information, see updates to my answer. –Arne Mertz Jun 27 '13 at 10:41 5 errno
your question and get tips & solutions from a community of 418,606 IT Pros & Developers. It's quick & easy. how to check write failure in ofstream?? P: n/a shyam HI I have a logging application https://bytes.com/topic/c/answers/478937-how-check-write-failure-ofstream wherin I create a ofstream object say, ofstream logger; by doing this logger.open(/* some path*/,ios_base:app); and then i do some logging by writing to this ofstream object like this logger << buffer << endl; here buffer is some string object http://karthikeyansukumaran.blogspot.com/2013/01/c-fstream-error-handling.html now my problem is that how to accurately check for write failure ( for example in case when disc is full) I have tried something like this logger.fail(); & also logger.bad(); but both these do not return true in case error handling of write failure.i am not sure if i can use these with o/p stream. I am sure theres got to be a way but I am a novice in c++ so I need some help in getting around this problem thanks shyam Apr 11 '06 #1 Post Reply Share this Question 5 Replies P: n/a veldwolf hi,shyam,i think if write failure,the system will throw a exception, so you may use try..catch to catch this exception. Apr 11 '06 #2 ofstream error handling P: n/a shyam veldwolf wrote: hi,shyam,i think if write failure,the system will throw a exception, so you may use try..catch to catch this exception. which particular exception should i catch ? can you give me an example using some pseudo code regards shyam Apr 11 '06 #3 P: n/a Tom Widmer shyam wrote: HI I have a logging application wherin I create a ofstream object say, ofstream logger; by doing this logger.open(/* some path*/,ios_base:app); and then i do some logging by writing to this ofstream object like this logger << buffer << endl; here buffer is some string object now my problem is that how to accurately check for write failure ( for example in case when disc is full) I have tried something like this logger.fail(); & also logger.bad(); but both these do not return true in case of write failure.i am not sure if i can use these with o/p stream. use !logger to check for any error, and then fail(), bad() and eof() to narrow things down. These should work. If not, what platform and compiler are you using? What exactly is the disk error you are causing (e.g. is it disk full, or something else, such as removing a memory stick halfway through the write operation)? You can also try "errno", which may give you extra information in a non-portable manner. Tom Apr 11 '06 #4 P: n/a Daniel T. In article <11**********************@z34g2000
data to a file and reading from a file respectively. These fstream classes are smart classes which would hide everything about working on the raw FILE pointer. These classes offer methods to verify if that file exists when trying to open a file or not. But when we reading or writing a file after that with the fstream objects, those APIs won't throw any exceptions or errors. You might think when that might happen....Let me put forward some real world examples when it might fail a) if the file you are creating in a share and the network goes down.. b) if the file you are creating is in a file share which is in a cluster, when the cluster group resource is taken offline after your write call. ... ... Below is an example where the issue might happen for the above said reasons.. #include