(octave.info)Formatted Input

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14.2.11 Formatted Input
-----------------------

Octave provides the ‘scanf’, ‘fscanf’, and ‘sscanf’ functions to read
formatted input.  There are two forms of each of these functions.  One
can be used to extract vectors of data from a file, and the other is
more ‘C-like’.

 -- : [VAL, COUNT, ERRMSG] = fscanf (FID, TEMPLATE, SIZE)
 -- : [V1, V2, ..., COUNT, ERRMSG] = fscanf (FID, TEMPLATE, "C")
     In the first form, read from FID according to TEMPLATE, returning
     the result in the matrix VAL.

     The optional argument SIZE specifies the amount of data to read and
     may be one of

     ‘Inf’
          Read as much as possible, returning a column vector.

     ‘NR’
          Read up to NR elements, returning a column vector.

     ‘[NR, Inf]’
          Read as much as possible, returning a matrix with NR rows.  If
          the number of elements read is not an exact multiple of NR,
          the last column is padded with zeros.

     ‘[NR, NC]’
          Read up to ‘NR * NC’ elements, returning a matrix with NR
          rows.  If the number of elements read is not an exact multiple
          of NR, the last column is padded with zeros.

     If SIZE is omitted, a value of ‘Inf’ is assumed.

     A string is returned if TEMPLATE specifies only character
     conversions.

     The number of items successfully read is returned in COUNT.

     If an error occurs, ERRMSG contains a system-dependent error
     message.

     In the second form, read from FID according to TEMPLATE, with each
     conversion specifier in TEMPLATE corresponding to a single scalar
     return value.  This form is more “C-like”, and also compatible with
     previous versions of Octave.  The number of successful conversions
     is returned in COUNT

     See the Formatted Input section of the GNU Octave manual for a
     complete description of the syntax of the template string.

     See also: Note: fgets, Note: fgetl, Note:
     fread, Note: scanf, Note: sscanf,
     Note: fopen.

 -- : [VAL, COUNT, ERRMSG] = scanf (TEMPLATE, SIZE)
 -- : [V1, V2, ..., COUNT, ERRMSG] = scanf (TEMPLATE, "C")
     This is equivalent to calling ‘fscanf’ with FID = ‘stdin’.

     It is currently not useful to call ‘scanf’ in interactive programs.

     See also: Note: fscanf, Note: sscanf, Note:
     printf.

 -- : [VAL, COUNT, ERRMSG, POS] = sscanf (STRING, TEMPLATE, SIZE)
 -- : [V1, V2, ..., COUNT, ERRMSG] = sscanf (STRING, TEMPLATE, "C")
     This is like ‘fscanf’, except that the characters are taken from
     the string STRING instead of from a stream.

     Reaching the end of the string is treated as an end-of-file
     condition.  In addition to the values returned by ‘fscanf’, the
     index of the next character to be read is returned in POS.

     See also: Note: fscanf, Note: scanf, Note:
     sprintf.

   Calls to ‘scanf’ are superficially similar to calls to ‘printf’ in
that arbitrary arguments are read under the control of a template
string.  While the syntax of the conversion specifications in the
template is very similar to that for ‘printf’, the interpretation of the
template is oriented more towards free-format input and simple pattern
matching, rather than fixed-field formatting.  For example, most ‘scanf’
conversions skip over any amount of “white space” (including spaces,
tabs, and newlines) in the input file, and there is no concept of
precision for the numeric input conversions as there is for the
corresponding output conversions.  Ordinarily, non-whitespace characters
in the template are expected to match characters in the input stream
exactly.

   When a “matching failure” occurs, ‘scanf’ returns immediately,
leaving the first non-matching character as the next character to be
read from the stream, and ‘scanf’ returns all the items that were
successfully converted.

   The formatted input functions are not used as frequently as the
formatted output functions.  Partly, this is because it takes some care
to use them properly.  Another reason is that it is difficult to recover
from a matching error.