Stream I/O

Article
11/16/2012

These functions process data in different sizes and formats, from single characters to large data structures. They also provide buffering, which can improve performance. The default size of a stream buffer is 4K. These routines affect only buffers created by the run-time library routines, and have no effect on buffers created by the operating system.

Stream I/O Routines

Routine	Use	.NET Framework equivalent
clearerr, clearerr_s	Clear error indicator for stream	Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.
fclose	Close stream	System::IO::Stream::Close, System::IO::BinaryReader::Close, System::IO::BinaryWriter::Close, System::IO::TextReader::Close, System::IO::TextWriter::Close, System::IO::StringReader::Close, System::IO::StringWriter::Close, System::IO::StreamReader::Close, System::IO::StreamWriter::Close
_fcloseall	Close all open streams except stdin, stdout, and stderr	System::IO::Stream::Close, System::IO::BinaryReader::Close, System::IO::BinaryWriter::Close, System::IO::TextReader::Close, System::IO::TextWriter::Close, System::IO::StringReader::Close, System::IO::StringWriter::Close, System::IO::StreamReader::Close, System::IO::StreamWriter::Close
_fdopen, wfdopen	Associate stream with file descriptor of open file	System::IO::FileStream::FileStream
feof	Test for end of file on stream	System::IO::FileStream::Read
ferror	Test for error on stream	Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.
fflush	Flush stream to buffer or storage device	System::IO::FileStream::Flush
fgetc, fgetwc	Read character from stream (function versions of getc and getwc)	System::IO::StreamReader::Read
_fgetchar, _fgetwchar	Read character from stdin (function versions of getchar and getwchar)	System::Console::Read
fgetpos	Get position indicator of stream	System::IO::FileStream::Position
fgets, fgetws	Read string from stream	System::IO::StreamReader::ReadLine, System::IO::TextReader::ReadBlock
_fileno	Get file descriptor associated with stream	System::IO::FileStream::Handle
_flushall	Flush all streams to buffer or storage device	System::IO::FileStream::Flush, System::IO::StreamWriter::Flush, System::IO::TextWriter::Flush, System::IO::BinaryWriter::Flush
fopen, _wfopen, fopen_s, _wfopen_s	Open stream	System::IO::File::Open
fprintf, _fprintf_l, fwprintf, _fwprintf_l, fprintf_s, _fprintf_s_l, fwprintf_s, _fwprintf_s_l	Write formatted data to stream	System::IO::StreamWriter::Write
fputc, fputwc	Write a character to a stream (function versions of putc and putwc)	System::IO::StreamWriter::Write
_fputchar, _fputwchar	Write character to stdout (function versions of putchar and putwchar)	System::Console::Write
fputs, fputws	Write string to stream	System::IO::StreamWriter::Write
fread	Read unformatted data from stream	System::IO::FileStream::Read
freopen, _wfreopen, freopen_s, _wfreopen_s	Reassign FILE stream pointer to new file or device	System::IO::File::Open
fscanf, fwscanf, fscanf_s, _fscanf_s_l, fwscanf_s, _fwscanf_s_l	Read formatted data from stream	System::IO::StreamReader::ReadLine; see also Parse methods, such as System::Double::Parse.
fseek, _fseeki64	Move file position to given location	System::IO::FileStream::Position, System::IO::FileStream::Seek
fsetpos	Set position indicator of stream	System::IO::FileStream::Position
_fsopen, _wfsopen	Open stream with file sharing	Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.
ftell, _ftelli64	Get current file position	System::IO::FileStream::Position
fwrite	Write unformatted data items to stream	System::IO::FileStream::Write
getc, getwc	Read character from stream (macro versions of fgetc and fgetwc)	System::IO::StreamReader::Read
getchar, getwchar	Read character from stdin (macro versions of fgetchar and fgetwchar)	System::Console::Read
_getmaxstdio	Returns the number of simultaneously open files permitted at the stream I/O level.	Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.
gets, getws, gets_s, _getws_s	Read line from stdin	System::Console::Read
_getw	Read binary int from stream	Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.
printf, _printf_l, wprintf, _wprintf_l,printf_s, _printf_s_l, wprintf_s, _wprintf_s_l	Write formatted data to stdout	System::Console::Write
putc, putwc	Write character to a stream (macro versions of fputc and fputwc)	System::IO::StreamWriter::Write
putchar, putwchar	Write character to stdout (macro versions of fputchar and fputwchar)	System::Console::Write
puts, _putws	Write line to stream	System::Console::Write
_putw	Write binary int to stream	Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.
rewind	Move file position to beginning of stream	Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.
_rmtmp	Remove temporary files created by tmpfile	Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.
scanf, _scanf_l, wscanf, _wscanf_l,scanf_s, _scanf_s_l, wscanf_s, _wscanf_s_l	Read formatted data from stdin	System::Console::ReadLine; see also Parse methods, such as System::Double::Parse.
setbuf	Control stream buffering	Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.
_setmaxstdio	Set a maximum for the number of simultaneously open files at the stream I/O level.	Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.
setvbuf	Control stream buffering and buffer size	Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.
_snprintf, _snwprintf, _snprintf_s, _snprintf_s_l, _snwprintf_s, _snwprintf_s_l	Write formatted data of specified length to string	Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.
_snscanf, _snwscanf, _snscanf_s, _snscanf_s_l, _snwscanf_s, _snwscanf_s_l	Read formatted data of a specified length from the standard input stream.	Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.
sprintf, swprintf, sprintf_s, _sprintf_s_l, swprintf_s, _swprintf_s_l	Write formatted data to string	System::String::Format
sscanf, swscanf, sscanf_s, _sscanf_s_l, swscanf_s, _swscanf_s_l	Read formatted data from string	See Parse methods, such as System::Double::Parse
_tempnam, _wtempnam	Generate temporary filename in given directory	Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.
tmpfile, tmpfile_s	Create temporary file	Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.
tmpnam, _wtmpnam, tmpnam_s, _wtmpnam_s	Generate temporary filename	Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.
ungetc, ungetwc	Push character back onto stream	Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.
_vcprintf, _vcwprintf, _vcprintf_s, _vcprintf_s_l, _vcwprintf_s, _vcwprintf_s_l	Write formatted data to the console.	System::Console::Write
vfprintf, vfwprintf, vfprintf_s, _vfprintf_s_l, vfwprintf_s, _vfwprintf_s_l	Write formatted data to stream	Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.
vprintf, vwprintf, vprintf_s, _vprintf_s_l, vwprintf_s, _vwprintf_s_l	Write formatted data to stdout	System::Console::Write
_vsnprintf, _vsnwprintf, vsnprintf_s, _vsnprintf_s, _vsnprintf_s_l, _vsnwprintf_s, _vsnwprintf_s_l	Write formatted data of specified length to buffer	Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.
vsprintf, vswprintf, vsprintf_s, _vsprintf_s_l, vswprintf_s, _vswprintf_s_l	Write formatted data to buffer	System::String::Format

When a program begins execution, the startup code automatically opens several streams: standard input (pointed to by stdin), standard output (pointed to by stdout), and standard error (pointed to by stderr). These streams are directed to the console (keyboard and screen) by default. Use freopen to redirect stdin, stdout, or stderr to a disk file or a device.

Files opened using the stream routines are buffered by default. The stdout and stderr functions are flushed whenever they are full or, if you are writing to a character device, after each library call. If a program terminates abnormally, output buffers may not be flushed, resulting in loss of data. Use fflush or _flushall to ensure that the buffer associated with a specified file or all open buffers are flushed to the operating system, which can cache data before writing it to disk. The commit-to-disk feature ensures that the flushed buffer contents are not lost in the event of a system failure.

There are two ways to commit buffer contents to disk:

Link with the file COMMODE.OBJ to set a global commit flag. The default setting of the global flag is n, for "no-commit."
Set the mode flag to c with fopen or _fdopen.

Any file specifically opened with either the c or the n flag behaves according to the flag, regardless of the state of the global commit/no-commit flag.

If your program does not explicitly close a stream, the stream is automatically closed when the program terminates. However, you should close a stream when your program finishes with it, as the number of streams that can be open at one time is limited. See _setmaxstdio for information on this limit.

Input can follow output directly only with an intervening call to fflush or to a file-positioning function (fseek, fsetpos, or rewind). Output can follow input without an intervening call to a file-positioning function if the input operation encounters the end of the file.

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Stream I/O

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