2/1/2024 0 Comments Istream open![]() The only way to detect whether something has gone wrong bad() are only set after you try toĪccess a stream. On a file, however, where we can go back and read things we’ve seen User has pressed Ctrl-D won’t help, because the stream really has ended. Succeeds depends on whether the stream was just temporarily broken or hasĪctually stopped working completely. Reset the stream to a state where you can use it again whether this clear() – Clears all the bad/EOF/fail state flags. Not only will attempts to access it fail, but it’s not possible to get bad() – If this is true, then the stream has gone bad. While(cin > i) what we are actually doing is while(!cin.fail()).) Failure is not a permanent error: in some cases its possible This could be because the stream was already EOF, or for some fail() – If this is true, then the last attempt to accessed the streamįailed. Way to the end of the file, or for network streams if the network User presses Ctrl-D, but it is also true for files if we read all the eof() – If this is true, then we have reached the end of the stream,Īnd trying to read from it will fail. good() – If this is true, then everything is OK with the stream. Have we reached the end of the stream? Has some kind of error occured? The The state flags for a stream tell us what state it is in: is everything OK? "End of File”, but more generally it means end of stream, no more data For example, for cin cin.eof() is true if the user has pressed Ctrl-D. Us information about the state of the stream. You look at what ios can do, you know that any stream can do those things Every stream class inherits from ios, so if Never really use this class by itself, as it exists only to specify what kinds Say “class X inherits from Y” (or “ X is a subclass of Y) this meansĪt the root of the stream is the class ios (defined in header ). what() from it’s parent class, exception. For example, the exception class logic_error “borrows” ![]() This is a way to “borrow” parts of one class when buildingĪnother class. The standard stream hierarchy encodesīoth the exception hierarchy and the stream hierarchy are built using Moving around in the stream to read things you’ve already read Some streams (like cout) can only be written to, some (like cin) can Just as exceptions are grouped into a hierarchy, so are streams. An iostream file can be read and written to, youĬan even write something out and then read it back in! The standard stream hierarchy If you have an istream-like file, you can only read from it an ostream-likeįile can only be written to. You’ve seen two already:įiles can be ostreams, istreams, or both, depending on how you access them. An istream is anything that you can read from: An ostream is anything that you can write In fact, a lot of things are “like” that, so the C++ committeeĬame up with ostreams and istreams. To the screen, and similarly, reading from a file is a lot like reading from The basic idea behind iostreams is that writing to a file is a lot like writing Information to a file (or maybe both)? In C++, this is easy, thanks to something Reads in the contents of a file and does something with it, or else writes out How do we access files in C++? That is, how do we write a program that either
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