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The following functions create strings, either from scratch, or by
putting strings together, or by taking them apart.
- Function: make-string COUNT CHARACTER
This function returns a string made up of COUNT repetitions of
CHARACTER. If COUNT is negative, an error is signaled.
(make-string 5 ?x)
(make-string 0 ?x)
Other functions to compare with this one include `char-to-string'
(Note: String Conversion.), `make-vector' (Note: Vectors.), and
`make-list' (Note: Building Lists.).
- Function: substring STRING START &optional END
This function returns a new string which consists of those
characters from STRING in the range from (and including) the
character at the index START up to (but excluding) the character
at the index END. The first character is at index zero.
(substring "abcdefg" 0 3)
Here the index for `a' is 0, the index for `b' is 1, and the index
for `c' is 2. Thus, three letters, `abc', are copied from the
full string. The index 3 marks the character position up to which
the substring is copied. The character whose index is 3 is
actually the fourth character in the string.
A negative number counts from the end of the string, so that -1
signifies the index of the last character of the string. For
(substring "abcdefg" -3 -1)
In this example, the index for `e' is -3, the index for `f' is -2,
and the index for `g' is -1. Therefore, `e' and `f' are included,
and `g' is excluded.
When `nil' is used as an index, it falls after the last character
in the string. Thus:
(substring "abcdefg" -3 nil)
Omitting the argument END is equivalent to specifying `nil'. It
follows that `(substring STRING 0)' returns a copy of all of
(substring "abcdefg" 0)
But we recommend `copy-sequence' for this purpose (Note: Sequence
A `wrong-type-argument' error is signaled if either START or END
are non-integers. An `args-out-of-range' error is signaled if
START indicates a character following END, or if either integer is
out of range for STRING.
Contrast this function with `buffer-substring' (Note: Buffer
Contents.), which returns a string containing a portion of the
text in the current buffer. The beginning of a string is at index
0, but the beginning of a buffer is at index 1.
- Function: concat &rest SEQUENCES
This function returns a new string consisting of the characters in
the arguments passed to it. The arguments may be strings, lists
of numbers, or vectors of numbers; they are not themselves
changed. If no arguments are passed to `concat', it returns an
(concat "abc" "-def")
(concat "abc" (list 120 (+ 256 121)) )
(concat "The " "quick brown " "fox.")
=> "The quick brown fox."
The second example above shows how characters stored in strings are
taken modulo 256. In other words, each character in the string is
stored in one byte.
The `concat' function always constructs a new string that is not
`eq' to any existing string.
When an argument is an integer (not a sequence of integers), it is
converted to a string of digits making up the decimal printed
representation of the integer. This special case exists for
compatibility with Mocklisp, and we don't recommend you take
advantage of it. If you want to convert an integer in this way,
use `format' (Note: Formatting Strings.) or `int-to-string'
(Note: String Conversion.).
(concat 54 321)
For information about other concatenation functions, see the
description of `mapconcat' in Note: Mapping Functions, `vconcat'
in Note: Vectors, and `append' in Note: Building Lists.
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