Octave provides the
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’.
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
Read as much as possible, returning a column vector.
Read up to nr elements, returning a column vector.
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.
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.
This is equivalent to calling
fscanf with fid =
It is currently not useful to call
scanf in interactive programs.
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.
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
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. For example, note that
sscanf parses the string and whitespace differently when using
mixed numeric and string output types:
teststr = "1 is a lonely number"; sscanf (teststr, "%s is a %s") ⇒ 1lonelynumber sscanf (teststr, "%g is a %s") ⇒ 1 108 111 110 101 108 121 [a, b, c] = sscanf ("1 is a lonely number", "%g is a %s %s", "C") ⇒ a = 1 ⇒ b = lonely ⇒ c = number
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
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.
The specific flags and modifiers that are permitted in the template string and their interpretation are all described in more detail in the following sections.