Section: Variables and Arrays
string array type that operates very
much as you would expect. Strings are stored internally as
8-bit values, and are otherwise similar to numerical arrays in
all respects. In some respects, this makes strings arrays
less useful than one might imagine. For example, numerical
arrays in 2-D are rectangular. Thus, each row in the array
must have the same number of columns. This requirement is
natural for numerical arrays and matrices, but consider a
string array. If one wants to store multiple strings in
a single data structure, they must all be the
same length (unlikely). The alternative is to use a cell
array of strings, in which case, each string can be of
arbitrary length. Most of the functions that support
strings in a set-theoretic way, like unique and sort
operate on cell-arrays of strings instead of string arrays.
Just to make the example concrete, here is the old way of
storing several strings in an array:
--> % This is an error
--> A = ['hello';'bye']
Error: Mismatch in dimension for rows in matrix definition
--> % This is OK, but awkward
--> A = ['hello';'bye ']
A =
hello
bye
--> % This is the right way to do it
--> A = {'hello','bye'}
A =
['hello'] ['bye']
One important (tricky) point in FreeMat is the treatment
of escape sequences. Recall that in C programming, an
escape sequence is a special character that causes the output
to do something unusual. FreeMat supports the following
escape sequences:
- causes a tab to be output
- causes a carriage return (return to the beginning
of the line of output, and overwrite the text)
- causes a linefeed (advance to next line)
Unix/Linux convention, that a
causes both a carriage return and a linefeed.
To put a single quote into a string use the MATLAB convention
of two single quotes, not the \' sequence. Here is an
example of a string containing some escape sequences:
--> a = 'I can''t use contractions Or can I? ' a = I can't use contractions Or can I?
Now, note that the string itself still contains the
characters. With the exception of the \', the escape
sequences do not affect the output unless the strings are
put through printf or fprintf. For example, if we
printf the variable a, we see the
and
take effect:
--> printf(a); I can't use contractions Or can I?
The final complicating factor is on MSWin systems. There,
filenames regularly contain \ characters. Thus, if you
try to print a string containing the filename
C:
edball imewarp
ewton.txt, the output will be mangled
because FreeMat thinks the
, and
are escape
sequences. You have two options. You can use disp to show
the filename (disp does not do escape translation to be
compatible with MATLAB). The second option is to escape the
backslashes in the string, so that the string you send to
printf contains C:\redball\timewarp\newton.txt.
--> % disp displays it ok --> a = 'C: edball imewarp ewton.txt' a = C: edball imewarp ewton.txt --> % printf makes a mess --> printf(a) C: edball imewarp ewton.txt--> % If we double up the slashes it works fine --> a = 'C:\redball\timewarp\newton.txt' a = C:\redball\timewarp\newton.txt --> printf(a) C: edball imewarp ewton.txt