# mopen

opens a file in Scilab

## Calling Sequence

    [fd, err] = mopen(file [, mode, swap ])

## Arguments

file

  a character string containing the path of the file to open.

mode

  a character string specifying the access mode requested for the file.

swap

  a scalar. If `swap` is present and `swap = 0` then automatic bytes swap is disabled.

  The default value is 1.

err

  a scalar. Error indicator.

  error value: | error message:
  0 | No error
  -1 | no more logical units
  -2 | cannot open file
  -3 | no more memory
  -4 | invalid name
  -5 | invalid status

fd

  a scalar: a file descriptor (it's a positive integer).

## Description

`mopen` may be used to open a `file` in a way compatible with the C `fopen` procedure. Without `swap` argument the `file` is supposed to be coded in "little endian IEEE format" and data are swapped if necessary to match the IEEE format of the processor.

The `mode` parameter controls the access type requested for the stream. The parameter can have one of the following values:

r

  opens for reading (default). The file must exist, otherwise it fails.

w

  opens for writing. If the file exists, its contents are destroyed.

a

  opens for appending. It creates the file if it does not exist.

r+

  opens for both reading and writing. The file must exist, otherwise it fails.

w+

  opens for both reading and writing. If the file exists, its contents are destroyed.

a+

  opens for both reading and appending. It creates the file if it does not exist.

In addition, the following characters can be used to specify the type of file:

t

  text file.

b

  binary file (default).

The default access mode is `'rb'` (binary file reading).

Note: on Windows, in text file mode, CR (carriage return) - LF (linefeed) combinations are translated into LF on reading, and LF are translated to CR-LF combinations on writing.

When you open a file for update, you can perform both input and output operations on the resulting stream. However, an output operation cannot be directly followed by an input operation without a file-positioning operation (`mseek` function). Also, an input operation cannot be directly followed by an output operation without an intervening file positioning operation, unless the input operation encounters the end of the file.

When you open a file for append (that is, when the `mode` parameter is `a` or `a+`), it is impossible to overwrite information already in the file. You can use the `mseek` function to reposition the file pointer to any position in the file, but when output is written to the file, the current file pointer is ignored. All output is written at the end of the file and the file pointer is repositioned to the end of the output.

To open files in a way compatible with Fortran-like functions use function `file`.

## Examples

    // open a SCI+'/ACKNOWLEDGEMENTS' as text and read only
    fd_r = mopen(SCI+'/ACKNOWLEDGEMENTS', 'rt')

    // read five lines of fd_r
    mgetl(fd_r, 5)

    // another way to read file
    // here read five words
    mfscanf(5, fd_r, '%s')

    // close file descriptor associated to SCI+'/ACKNOWLEDGEMENTS' as text and read only
    mclose(fd_r);

    // open a file as text with write property
    fd_w = mopen(TMPDIR+'/write.txt', 'wt');

    // write a line in fd_w
    mputl('This is a line of text', fd_w);
    mclose(fd_w);

    // read text
    fd_r2 = mopen(TMPDIR+'/write.txt', 'rt');
    mgetl(fd_r2)
    mclose(fd_r2);

    // read/write a file as binary

    // first we write file
    fd_wb = mopen(TMPDIR+'/writeread.bin', 'wb')

    // put values as binary
    mput(2003, 'l', fd_wb);
    mput(2008, 'i', fd_wb);
    mput(2012, 's', fd_wb);
    mput(98, 'c', fd_wb);

    // close file descriptor associated to TMPDIR+'/writeread.bin'
    mclose(fd_wb);

    // we read file
    fd_rb = mopen(TMPDIR+'/writeread.bin', 'rb')

    mget(fd_rb, 'l')
    mget(fd_rb, 'i')
    mget(fd_rb, 's')
    mget(fd_rb, 'c')

    mclose(fd_rb)

## See Also

- file
- mclose
- merror
- meof
- mfprintf
- fprintfMat
- mfscanf
- fscanfMat
- mget
- mgetl
- mgetstr
- mprintf
- mput
- mputl
- mputstr
- mseek
- mtell
- mdelete