Fstream Open Error Handling
Contents |
here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of
C++ Ifstream Error Handling
this site About Us Learn more about Stack Overflow the company Business ofstream fail Learn more about hiring developers or posting ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask ifstream::failure 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; it only takes a minute: Sign
Ifstream Open Fail
up When will ofstream::open fail? up vote 10 down vote favorite 2 I am trying out try, catch, throw statements in C++ for file handling, and I have written a dummy code to catch all errors. My question is in order to check if I have got these right, I need an error to occur. Now I can easily check infile.fail() by simply
C++ Ifstream Exceptions
not creating a file of the required name in the directory. But how will I be able to check the same for outfile.fail() (outfile is ofstream where as infile is ifstream). In which case, will the value for outfile.fail() be true? sample code [from comments on unapersson's answer, simplified to make issue clearer -zack]: #include
here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site About Us Learn more about Stack Overflow the company ifstream::failbit Business Learn more about hiring developers or posting ads with us Stack Overflow Questions Jobs
Ofstream Example
Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 4.7 million programmers, c++ file error handling just like you, helping each other. Join them; it only takes a minute: Sign up Error handling in std::ofstream while writing data up vote 1 down vote favorite I have a small program where i initialize a http://stackoverflow.com/questions/5835848/when-will-ofstreamopen-fail string and write to a file stream: #include does not encounter the above issue, hence I am unable to know why it failed. Please tell me, by http://stackoverflow.com/questions/28342660/error-handling-in-stdofstream-while-writing-data 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 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.
= ios_base::in | ios_base::out); void open (const string& filename, ios_base::openmode mode = ios_base::in | ios_base::out); Open file Opens the file identified by argument filename, associating it with the stream object, so that input/output operations are performed http://www.cplusplus.com/reference/fstream/fstream/open/ on its content. Argument mode specifies the opening mode. If the stream http://www.cplusplus.com/forum/beginner/6033/ is already associated with a file (i.e., it is already open), calling this function fails. The file association of a stream is kept by its internal stream buffer: Internally, the function calls rdbuf()->open(filename,mode) The function sets failbit in case of failure. The function clears the stream's state flags error handling on success (setting them to goodbit). In case of failure, failbit is set. Parameters filename String with the name of the file to open. Specifics about its format and validity depend on the library implementation and running environment. mode Flags describing the requested input/output mode for the file. This is an object of the bitmask member type openmode that consists of a combination fstream open error of the following member constants: member constantstands foraccess ininputFile open for reading: the internal stream buffer supports input operations. outoutputFile open for writing: the internal stream buffer supports output operations. binarybinaryOperations are performed in binary mode rather than text. ateat endThe output position starts at the end of the file. appappendAll output operations happen at the end of the file, appending to its existing contents. trunctruncateAny contents that existed in the file before it is open are discarded. These flags can be combined with the bitwise OR operator (|). If the mode has both trunc and app set, the opening operation fails. It also fails if either is set but out is not, or if both app and in are set. If the mode has both trunc and app set, the opening operation fails. It also fails if trunc is set but out is not. Return Value none If the function fails to open a file, the failbit state flag is set for the stream (which may throw ios_base::failure if that state flag was registered using member exceptions). Example 1 working. I'm asking the user to give me the name of a file. If the file doesn't exist or does not open, I want it to prompt them again until they give me a good file name. The code I'm using now is: 1
2
3
4
5
6
7
8
9
10
11
12
13
14
// fstream::open / fstream::close #include
2
3
4
5
6
7
8
9
10
11
12
do { cout << "\nPlease enter the file path: "; cin >> file; fileName.open(file.c_str( )); if (fileName.fail()) { cout << "\Error!"; fileName.clear( ); } }while (fileName.fail()); Everything works great if they give me a good file name, but that's it... If they give me a bad file name, it doesn't work. Any suggestions? S Dec 1, 2008 at 8:54pm UTC Return 0 (1282) You can use is_open() to check if the file was successfully opened. If file is ! open then cout the Error and force rentry via a loop. example of use: 1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
#include
2
cout << "\nPlease enter the file path: "; getli