Fstream Error

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C++ Ifstream Exceptions

them; it only takes a minute: Sign 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

Ifstream::failbit

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 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, c++ file error handling simplified to make issue clearer -zack]: #include using std::ofstream; int main() { ofstream outfile; outfile.open("test.txt"); if (outfile.fail()) // do something...... else // do something else..... return 0; } c++ share|improve this question edited Apr 29 '11 at 19:01 Robᵩ 82.7k677144 asked Apr 29 '11 at 18:25 Scranton 51113 add a comment| 3 Answers 3 active oldest votes up vote 14 down vote The open(2) man page on Linux has about 30 conditions. Some intresting ones are: If the file exists and you don't have permission to write it. If the file doesn't exist, and you don't have permission (on the diretory) to create it. If you don't have search permission on some parent directory. If you pass in a bogus char* for the filename. If, while opening a device file, you press CTRL-C. If the kernel encountered too many symbolic links while resolving the name. If you try to open a directory for writing. If the pathname is too long. If your process has too many files open already. If the system has too many files open already. If the pathname refers to a device file, and there is no such device in the system. If the kernel has run out of memory. If the filesystem is full. If a component of the pathname is not a directory. If the file is on a read-only filesystem. If the file is an executable f

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C++ Strerror

this site About Us Learn more about Stack Overflow the company Business strerror_s Learn more about hiring developers or posting ads with us Code Review Questions Tags Users Badges Unanswered Ask Question basic_ios::clear _ Code Review Stack Exchange is a question and answer site for peer programmer code reviews. Join them; it only takes a minute: Sign up Here's how it works: Anybody can ask http://stackoverflow.com/questions/5835848/when-will-ofstreamopen-fail a question Anybody can answer The best answers are voted up and rise to the top Better option than “errno” for file IO error handling up vote 10 down vote favorite 3 I have the following method for opening a file: void TankFile::OpenForReading(const std::string & filename) { assert(!filename.empty()); errno = 0; file.exceptions(0); // Don't throw file.open(filename, (std::fstream::in | std::fstream::binary)); if (!file.is_open() || !file.good()) http://codereview.stackexchange.com/questions/57829/better-option-than-errno-for-file-io-error-handling { const char * errorStr = strerror(errno); throw TankFileError(Format("Failed to open Tank file \"%s\": '%s'", filename.c_str(), errorStr)); } } The objective here is to attempt to open a file and throw TankFileError with a proper error description on failure. The caller will be expecting this exception type. Everything works fine and I get a nice error message like this if the exception is thrown: Failed to open Tank file "unexistent_file": 'No such file or directory' But what I don't like in that block is having to use the errno global and strerror(). A way around it would be to let the stream throw an exception, then catch it, get the error message from the what() member and re-throw with TankFileError, but I find this solution also a bit hackish, plus, in the tests I did, the resulting error message from std::fstream::failure was pretty cryptic: void TankFile::OpenForReading(const std::string & filename) { assert(!filename.empty()); try { file.exceptions(std::fstream::failbit); file.open(filename, (std::fstream::in | std::fstream::binary)); } catch (std::fstream::failure & err) { throw TankFileError(Format("Failed to open Tank file \"%s\": '%s'", filename.c_str(), err.what())); } } Produced the error message: Failed to open Tank file "unexistent_file": 'ios_bas

the following simple program: #include #include #include #include using namespace http://www.cplusplus.com/forum/beginner/13793/ std; int main(int argc, char *argv[]) { ifstream infile; infile.open("testFile.txt"); if http://www.cplusplus.com/reference/fstream/ifstream/ (infile.fail()) { cout << "file opening failed" << endl; } system("PAUSE"); exit (1); } When I run the program, I get the "file opening failed" message. I've tried variations in the code for opening the file, and they all seem to fail, although the fstream error file is clearly in the directory. For example, this code (taken from http://www.cplusplus.com/reference/iostream/ifstream/is_open/) also produces the error-opening-file message: // ifstream::is_open #include #include using namespace std; int main () { ifstream infile; infile.open ("testFile.txt"); if (infile.is_open()) { while (infile.good()) cout << "file opened successfully" << endl; infile.close(); } else { cout << "Error opening file"; ifstream open fail } return 0; } And this program also fails to open the file: #include #include #include #include using namespace std; void readInputFile (ifstream &infile, char buf[]); int main(int argc, char *argv[]) { string fileName; fileName= "mystring"; cout << "What is the file's name?" << endl; cin >> fileName; ifstream infile; infile.open(fileName.c_str()); char buf[1024]={0}; // Read file into array readInputFile (infile, buf); system("PAUSE"); return 0; } // FUNCTION DEFINITION void readInputFile (ifstream &infile, char buf[]) { if (infile.is_open()) { while (! infile.eof() ) { infile.read(&(buf[0]),1024); } cout << "File reading was successful" << endl; infile.close(); } else cout << "Unable to open file" << endl; } The strange thing is that similar code worked perfectly in the same computer and the same directory a few days ago. It seems that file opening somehow has stopped working. I suspect the problem is not the code, but something related to the directory; but what it is exactly, I have no idea. Any sugges

object as their internal stream buffer, which performs input/output operations on the file they are associated with (if any). File streams are associated with files either on construction, or by calling member open. This is an instantiation of basic_ifstream with the following template parameters: template parameterdefinitioncomments charTcharAliased as member char_type traitschar_traitsAliased as member traits_type Apart from the internal file stream buffer, objects of this class keep a set of internal fields inherited from ios_base, ios and istream: fieldmember functionsdescription Formattingformat flagsflagssetfunsetfA set of internal flags that affect how certain input/output operations are interpreted or generated. See member type fmtflags. field widthwidthWidth of the next formatted element to insert. display precisionprecisionDecimal precision for the next floating-point value inserted. localegetlocimbueThe locale object used by the function for formatted input/output operations affected by localization properties. fill characterfillCharacter to pad a formatted field up to the field width (width). Stateerror staterdstatesetstateclearThe current error state of the stream. Individual values may be obtained by calling good, eof, fail and bad. See member type iostate. exception maskexceptionsThe state flags for which a failure exception is thrown. See member type iostate. Othercallback stackregister_callbackStack of pointers to functions that are called when certain events occur. extensible arraysiwordpwordxallocInternal arrays to store objects of type long and void*. tied streamtiePointer to output stream that is flushed before each i/o operation on this stream. stream bufferrdbufPointer to the associated streambuf object, which is charge of all input/output operations. character countgcountCount of characters read by last unformatted input operation. Member types The class declares the following member types: member typedefinition char_typechar traits_typechar_traits int_typeint pos_typestreampos off_typestreamoff These member types are inherited from its base classes istream and ios_base: eventType to indicate event type (public member type )event_callbackEvent callback function type (public member type )failureBase class for stream except