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For historical reasons, the type of the C data structure that represents a stream is called FILE rather than "stream". This leads to unfortunate confusion over terminology in many books on C.
This manual, however, is careful to use the terms "file" and "stream" freopen stdin binary trading in the technical sense. FILE This is the data type used to represent stream objects. A FILE object holds all of the internal state information about the connection to the associated file, including such things as the file position indicator and buffering information.
Each stream also has error and end-of-file status indicators that can be tested with the ferror and feof functions; see section End-Of-File and Errors. Don't try to create your own objects of type FILE ; let the library do it. When the main function of your program is invoked, it already has three predefined freopen stdin binary trading open and available for use. These represent the "standard" input and output channels that have been established for the process.
In the GNU system, you can specify what files or processes correspond to these streams using the pipe and redirection facilities provided by the shell.
The primitives shells use to implement these facilities are described in section File System Interface. Most other operating systems provide similar mechanisms, but the details of how to use them can vary. In the GNU C library, stdinstdoutand stderr are normal variables which you can set just like any others. For example, to redirect the standard output to a freopen stdin binary trading, you could do:.
Note however, that in other systems stdinstdoutand stderr are macros that you cannot assign to in the normal way. But you can use freopen to get the effect of closing one and reopening it. See section Opening Streams. Opening a file with the fopen function creates a new stream freopen stdin binary trading establishes a connection between the stream and a file. This may involve creating a new file. The opentype argument is a string that controls how the freopen stdin binary trading is opened and specifies attributes of the resulting stream.
It must begin with one of the following sequences of characters:. The ANSI standard says that when using such a stream, you must call fflush see section Stream Buffering or a file positioning function such as fseek see section File Positioning when switching from reading to writing or vice versa.
Otherwise, internal buffers might not be emptied properly. The GNU C library does not have this limitation; you can do arbitrary reading and writing operations on a stream in whatever order. The GNU C library defines one additional character for use in opentype: See section Text and Binary Streams. Any other characters in opentype are simply ignored.
They may be meaningful in other systems. You can have multiple streams or file descriptors pointing to the same file open at the same time. If you do only input, this works straightforwardly, but you must be careful if any output streams are included. See section Dangers of Mixing Streams and Descriptors. This is equally true whether the streams freopen stdin binary trading in one program not usual or in several programs which can easily happen.
It may be advantageous to use the file locking facilities to avoid simultaneous access. See section File Locks. You might be able to open more than this many streams, but that is not guaranteed. The value of this constant is at least eight, which includes the three standard streams stdinstdoutand stderr. It first closes the stream referred to by streamignoring any errors that are detected in the process.
Because errors are ignored, you should not use freopen on an output stream if you have actually done any output using the stream. Then the file named by filename is opened with mode opentype as for fopenand associated with the same stream object stream.
If the operation fails, a null pointer is returned; otherwise, freopen freopen stdin binary trading stream. This is useful in programs in which use of a standard stream for certain purposes is hard-coded. In the GNU C library, you can simply close the standard streams and open new ones with fopen.
But other systems lack this ability, so using freopen is more portable. When a stream is closed with fclosethe connection between the stream and the file is cancelled. After you have closed a stream, you cannot perform any additional operations on it. Any buffered output is written and any buffered input is discarded. The fclose function returns a value of 0 if the file was closed successfully, and EOF if an error was detected. It is important to check for errors when you call fclose to close an output stream, because real, everyday errors can be detected at this time.
For example, when fclose writes the remaining buffered output, freopen stdin binary trading might get an error because the disk is full. Even if you know the buffer is empty, errors can still occur when closing a file if you are using NFS. If the main function to your program returns, or if you call the exit function see section Normal Terminationall open streams are automatically closed properly. If your program terminates in any other manner, such as by calling the abort function see section Aborting a Program or from a fatal signal see section Signal Handlingopen streams might not be closed properly.
Buffered output might not be flushed and files may be incomplete. For more information on buffering of streams, see section Stream Buffering. This section describes functions for performing character- and line-oriented output. EOF is returned if a write error occurs; otherwise the character c is returned.
One consequence is that freopen stdin binary trading may evaluate the stream argument more than once. The terminating null character is not written. This function does not add a newline character, either.
It outputs only the chars in the string. This function returns EOF if a write error occurs, and otherwise a non-negative value. The terminating null character of the string is not written. This section describes freopen stdin binary trading for performing character- and line-oriented input. If an end-of-file condition or read freopen stdin binary trading occurs, EOF is returned instead.
Here is an example freopen stdin binary trading a function that does input using fgetc. It would work just as well using getc instead, or using getchar instead of fgetc stdin. It's provided for compatibility with SVID. Since many programs interpret input on the basis of lines, it's convenient to have functions to read a line freopen stdin binary trading text from a stream.
Standard C has functions to freopen stdin binary trading this, but they aren't very safe: So the GNU library provides the nonstandard getline function that makes it easy to read lines reliably. Another GNU extension, getdelimgeneralizes getline. It reads a delimited record, defined as everything through the next occurrence of a specified delimiter character.
If this buffer is long enough to hold the line, getline stores the line in this buffer. See section Unconstrained Allocation. When getline is successful, it returns the number of characters read including the newline, but not including the terminating null. This value enables you to distinguish null characters that are part of the line from the null character inserted as a terminator.
This function is a GNU extension, but it is the recommended way to read lines from a stream. The alternative standard functions are unreliable. Freopen stdin binary trading an error occurs or end of file is reached, getline returns The argument delimiter specifies the delimiter character; getdelim keeps reading until it sees that character or end freopen stdin binary trading file. The text is stored in lineptrincluding the delimiter character and a terminating null.
Like getlinegetdelim makes lineptr bigger if it isn't big enough. You must supply count characters worth of space in sbut the number of characters read is at most count - 1.
The extra character space is used to hold the null character at the end of the string. If the system is already at end of file when you call fgetsthen the freopen stdin binary trading of the array s are unchanged and a null pointer is returned.
A null pointer is also returned if a read error occurs. Otherwise, the return value is the pointer s. If the input data has a null character, you can't tell. So don't use fgets unless you know the data cannot contain freopen stdin binary trading null. Don't use it to read files edited by the user because, if the user inserts a null character, you should either handle it properly or print a clear error message.
We recommend using getline instead of fgets. The newline character is discarded note that this differs from the behavior of fgetswhich copies the newline character into the string. If gets encounters a read error or end-of-file, it returns a null pointer; otherwise it returns s.
The gets function is very dangerous because it provides no protection against overflowing the string s. The GNU library includes it for compatibility only. You should freopen stdin binary trading use fgets or getline instead. To remind you of this, the linker if using GNU ld will issue a warning whenever you use gets.
In parser programs it is often useful to freopen stdin binary trading the next character in the input stream without removing it from the stream. This is called "peeking ahead" freopen stdin binary trading the input freopen stdin binary trading your freopen stdin binary trading gets a glimpse of the input it will read next.