5.3.1 Concatenating Strings

Strings can be concatenated using matrix notation (see Strings, 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 cat, horzcat, and 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 (see 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 (see 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: strvcat, 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: char, strcat, 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: cstrcat, char, 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: strcat, char, strvcat.