fstream open

프로그래밍/C++ 2009. 4. 22. 11:02

void open ( const char * filename,
            ios_base::openmode mode = ios_base::in | ios_base::out );

Open file

Opens a file whose name is s, associating its content with the stream object to perform input/output operations on it. The operations allowed and some operating details depend on parameter mode.

The function effectively calls rdbuf()->open(filename,mode).

If the object already has a file associated (open), the function fails.

On failure, the failbit flag is set (which can be checked with member fail), and depending on the value set with exceptions an exception may be thrown.

Parameters

filename

C-string containing the name of the file to be opened.

mode

Flags describing the requested i/o mode for the file. This is an object of type ios_base::openmode, which consists on a combination of one or more of the following flags defined as member constants:

flag value	opening mode
`app`	(append) Set the stream's position indicator to the end of the stream before each output operation.
`ate`	(at end) Set the stream's position indicator to the end of the stream on opening.
`binary`	(binary) Consider stream as binary rather than text.
`in`	(input) Allow input operations on the stream.
`out`	(output) Allow output operations on the stream.
`trunc`	(truncate) Any current content is discarded, assuming a length of zero on opening.

Return Value

none

Example

// fstream::open
#include <fstream>
using namespace std;

int main () {

  fstream filestr;

  filestr.open ("test.txt", fstream::in | fstream::out | fstream::app);

  // >> i/o operations here <<

  filestr.close();

  return 0;
}

This example opens a file to append content.