Basic Fstream Error Handling
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Ifstream::failure
ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join c++ ofstream error handling 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 ifstream::failbit a minute: Sign up C++ ifstream Error Checking up vote 11 down vote favorite 3 I am new to C++ and want to add error checking to my code plus I want to make sure I'm using good coding practices. I
Ifstream Exceptions
read a line from an ASCII file into a string using: ifstream paramFile; string tmp; //open input file tmp.clear(); paramFile >> tmp; //parse tmp How can I error check to make sure the input file read was successful? I'm seeing much more complicated ways of reading from an ASCII file out there. Is the way I'm doing it "safe/robust"? c++ error-handling ifstream share|improve this question edited Nov 19 '12 at 1:51 Lightness Races in Orbit 216k34332580 asked Nov 19 '12 at 1:36
Ofstream Fail
slowmotionfred 63117 1 std::string's default constructor makes an empty string. No need for the clear(). Also, if you want a line, use std::getline. –chris Nov 19 '12 at 1:38 Thanks for the link lightness –slowmotionfred Nov 19 '12 at 1:59 add a comment| 1 Answer 1 active oldest votes up vote 8 down vote accepted paramFile >> tmp; If the line contains spaces, this will not read the whole line. If you want that use std::getline(paramFile, tmp); which reads up until the newline. Basic error checking is done by examining the return values. For example: if(paramFile>>tmp) // or if(std::getline(paramFile, tmp)) { std::cout << "Successful!"; } else { std::cout << "fail"; } operator>> and std::getline both return a reference to the stream. The stream evaluates to a boolean value which you can check after the read operation. The above example will only evaluate to true if the read was successful. Here is an example of how I might make your code: ifstream paramFile("somefile.txt"); // Use the constructor rather than `open` if (paramFile) // Verify that the file was open successfully { string tmp; // Construct a string to hold the line while(std::getline(paramFile, tmp)) // Read file line by line { // Read was successful so do something with the line } } else { cerr << "File could not be opened!\n"; // Report error cerr << "Error code: " << strerror(errno); // Get some info as to why } share|improve t
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C++ File Error Handling
posting ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow c++ strerror 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 up Exception Handling and Opening a File? up vote 18 http://stackoverflow.com/questions/13446593/c-ifstream-error-checking down vote favorite 1 Is it possible to use exceptions with file opening as an alternative to using .is_open()? For example: ifstream input; try{ input.open("somefile.txt"); }catch(someException){ //Catch exception here } If so, what type is someException? c++ exception-handling inputstream file-handling share|improve this question edited Sep 26 '12 at 0:15 Bill the Lizard 221k138446737 asked Mar 12 '12 at 15:56 Moshe 30.2k55208355 1 en.cppreference.com/w/cpp/io/basic_ios/exceptions –R. Martinho Fernandes Mar http://stackoverflow.com/questions/9670396/exception-handling-and-opening-a-file 12 '12 at 16:01 add a comment| 3 Answers 3 active oldest votes up vote 20 down vote accepted http://en.cppreference.com/w/cpp/io/basic_ios/exceptions // ios::exceptions #include
fstream Donate $1 now to see this question answered quickly Sponsored questions offer a monetary incentive to answerers to produce quality responses. Be intelligently matched with 5 likely answerers who will be alerted to help. 2Contributors 2Replies 4Views 5 https://www.daniweb.com/programming/software-development/threads/350603/handle-exception-on-fstream YearsDiscussion Span 5 Years Ago Last Post by TheFueley 0 5 Years Ago https://gehrcke.de/2011/06/reading-files-in-c-using-ifstream-dealing-correctly-with-badbit-failbit-eofbit-and-perror/ I'm having trouble figuring out how to use exceptions to check if a file stream was created successfully. I know I can use if statements, but how do I do this using try/catch statements? It compiles successfully but it gives me an error when I supply a non-existent filename as an argument. If I supply error handling a file that does exist, it runs fine. The message I get when I give it a bogus filename is: terminate called after throwing an instance of 'char*' Abort trap #include
Motivated by this POV-Ray issue I tried to find a reliable way to read a file line by line in C++ using std::ifstream in combination with std::getline(). While doing so, the goal was to handle all underlying stream errors as well as file opening errors, and to emit as precise error messages as possible. In a high-level programming language such as Python this level of reliability and usability is not difficult to obtain. However, in C++ this turned out to be a rather complex topic. Proper handling of the stream error bits eofbit, failbit, and badbit requires a tremendous amount of care, as discussed for example here, here, and here, and finally at cplusplus.com. It is worth mentioning that although cplusplus.com is a convenient reference, it does not provide us with a rock-solid solution for the above-stated problem and also does not mention all the important details. When it comes to the idea of providing meaningful error messages, things become quite complicated. Proper evaluation of errno, respectively perror(), in response to the stream error bits is not a trivial task as can be inferred from discussions like this and this. From these discussions we learn that most of the related uncertainty comes from a lack of centralized documentation or even missing documentation. The exact behavior of C++ code with respect to file handling and stream manipulation is defined by an intertwining of language specification (C++ in this case), operating system interface (e.g. POSIX) and low-level APIs (provided by e.g. libc) -- they all are documented in different places and to a different extent. We for example expect that when fopen() returns NULL, errno is set to something meaningful. But where is this actually documented? In order to understand the relation between the language and operating system constructs involved, I performed quite some research and testing. Of course there are many obvious and non-obvious ways to write unreliable code. As expected, for writing reliable code, there also best practices or "recipes" to follow. To name, explain, and share those with the community is the goal of this article. We all know that re-using established recipes saves time and improves software quality in the long-term. Update (January 18th, 2015): In the mean time, this article has made it into the top Google search results for "c++ read file ifst