(octave.info)Concatenating Strings

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5.3.1 Concatenating Strings
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Strings can be concatenated using matrix notation (Note: Strings,
Note: Character Arrays) which is often the most natural method.  For
example:

     fullname = [fname ".txt"];
     email = ["<" user "@" domain ">"];

In each case it is easy to see what the final string will look like.
This method is also the most efficient.  When using matrix concatenation
the parser immediately begins joining the strings without having to
process the overhead of a function call and the input validation of the
associated function.

   Nevertheless, there are several other functions for concatenating
string objects which can be useful in specific circumstances: ‘char’,
‘strvcat’, ‘strcat’, and ‘cstrcat’.  Finally, the general purpose
concatenation functions can be used: see Note: cat, Note:
horzcat, and Note: vertcat.

   • All string concatenation functions except ‘cstrcat’ convert
     numerical input into character data by taking the corresponding
     ASCII character for each element, as in the following example:

          char ([98, 97, 110, 97, 110, 97])
             ⇒ banana

   • ‘char’ and ‘strvcat’ concatenate vertically, while ‘strcat’ and
     ‘cstrcat’ concatenate horizontally.  For example:

          char ("an apple", "two pears")
              ⇒ an apple
                 two pears

          strcat ("oc", "tave", " is", " good", " for you")
               ⇒ octave is good for you

   • ‘char’ generates an empty row in the output for each empty string
     in the input.  ‘strvcat’, on the other hand, eliminates empty
     strings.

          char ("orange", "green", "", "red")
              ⇒ orange
                 green

                 red

          strvcat ("orange", "green", "", "red")
              ⇒ orange
                 green
                 red

   • All string concatenation functions except ‘cstrcat’ also accept
     cell array data (Note: Cell Arrays).  ‘char’ and ‘strvcat’
     convert cell arrays into character arrays, while ‘strcat’
     concatenates within the cells of the cell arrays:

          char ({"red", "green", "", "blue"})
               ⇒ red
                  green

                  blue

          strcat ({"abc"; "ghi"}, {"def"; "jkl"})
               ⇒
                  {
                    [1,1] = abcdef
                    [2,1] = ghijkl
                  }

   • ‘strcat’ removes trailing white space in the arguments (except
     within cell arrays), while ‘cstrcat’ leaves white space untouched.
     Both kinds of behavior can be useful as can be seen in the
     examples:

          strcat (["dir1";"directory2"], ["/";"/"], ["file1";"file2"])
               ⇒ dir1/file1
                  directory2/file2

          cstrcat (["thirteen apples"; "a banana"], [" 5$";" 1$"])
                ⇒ thirteen apples 5$
                   a banana        1$

     Note that in the above example for ‘cstrcat’, the white space
     originates from the internal representation of the strings in a
     string array (Note: Character Arrays).

 -- : char (X)
 -- : char (X, ...)
 -- : char (S1, S2, ...)
 -- : char (CELL_ARRAY)
     Create a string array from one or more numeric matrices, character
     matrices, or cell arrays.

     Arguments are concatenated vertically.  The returned values are
     padded with blanks as needed to make each row of the string array
     have the same length.  Empty input strings are significant and will
     concatenated in the output.

     For numerical input, each element is converted to the corresponding
     ASCII character.  A range error results if an input is outside the
     ASCII range (0-255).

     For cell arrays, each element is concatenated separately.  Cell
     arrays converted through ‘char’ can mostly be converted back with
     ‘cellstr’.  For example:

          char ([97, 98, 99], "", {"98", "99", 100}, "str1", ["ha", "lf"])
             ⇒ ["abc "
                 "    "
                 "98  "
                 "99  "
                 "d   "
                 "str1"
                 "half"]

     See also: Note: strvcat, Note: cellstr.

 -- : strvcat (X)
 -- : strvcat (X, ...)
 -- : strvcat (S1, S2, ...)
 -- : strvcat (CELL_ARRAY)
     Create a character array from one or more numeric matrices,
     character matrices, or cell arrays.

     Arguments are concatenated vertically.  The returned values are
     padded with blanks as needed to make each row of the string array
     have the same length.  Unlike ‘char’, empty strings are removed and
     will not appear in the output.

     For numerical input, each element is converted to the corresponding
     ASCII character.  A range error results if an input is outside the
     ASCII range (0-255).

     For cell arrays, each element is concatenated separately.  Cell
     arrays converted through ‘strvcat’ can mostly be converted back
     with ‘cellstr’.  For example:

          strvcat ([97, 98, 99], "", {"98", "99", 100}, "str1", ["ha", "lf"])
                ⇒ ["abc "
                    "98  "
                    "99  "
                    "d   "
                    "str1"
                    "half"]

     See also: Note: char, Note: strcat, Note:
     cstrcat.

 -- : strcat (S1, S2, ...)
     Return a string containing all the arguments concatenated
     horizontally.

     If the arguments are cell strings, ‘strcat’ returns a cell string
     with the individual cells concatenated.  For numerical input, each
     element is converted to the corresponding ASCII character.
     Trailing white space for any character string input is eliminated
     before the strings are concatenated.  Note that cell string values
     do *not* have whitespace trimmed.

     For example:

          strcat ("|", " leading space is preserved", "|")
              ⇒ | leading space is preserved|

          strcat ("|", "trailing space is eliminated ", "|")
              ⇒ |trailing space is eliminated|

          strcat ("homogeneous space |", "  ", "| is also eliminated")
              ⇒ homogeneous space || is also eliminated

          s = [ "ab"; "cde" ];
          strcat (s, s, s)
              ⇒
                  "ababab   "
                  "cdecdecde"

          s = { "ab"; "cd " };
          strcat (s, s, s)
              ⇒
                  {
                    [1,1] = ababab
                    [2,1] = cd cd cd
                  }

     See also: Note: cstrcat, Note: char, Note:
     strvcat.

 -- : cstrcat (S1, S2, ...)
     Return a string containing all the arguments concatenated
     horizontally with trailing white space preserved.

     For example:

          cstrcat ("ab   ", "cd")
                ⇒ "ab   cd"

          s = [ "ab"; "cde" ];
          cstrcat (s, s, s)
                ⇒ "ab ab ab "
                   "cdecdecde"

     See also: Note: strcat, Note: char, Note:
     strvcat.