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📜  LISP-字符串

📅  最后修改于: 2020-11-03 07:13:21             🧑  作者: Mango

Common Lisp中的字符串是向量，即一维字符数组。

字符串字面量用双引号引起来。字符集支持的任何字符都可以用双引号引起来，以构成一个字符串，除了双引号字符(“)和转义字符(\)之外。但是，可以通过用反斜杠(\)进行转义来包括这些字符。

例

创建一个名为main.lisp的新源代码文件，然后在其中键入以下代码。

现场演示
(write-line "Hello World")
(write-line "Welcome to Tutorials Point")

;escaping the double quote character
(write-line "Welcome to \"Tutorials Point\"")

当您执行代码时，它返回以下结果-

Hello World
Welcome to Tutorials Point
Welcome to "Tutorials Point"

字符串比较功能

数值比较函数和运算符(例如<和>)不适用于字符串。通用LISP提供了另外两组函数来比较代码中的字符串。一组区分大小写，另一组不区分大小写。

下表提供了功能-

Case Sensitive Functions Case-insensitive Functions Description
string= string-equal Checks if the values of the operands are all equal or not, if yes then condition becomes true.
string/= string-not-equal Checks if the values of the operands are all different or not, if values are not equal then condition becomes true.
string< string-lessp Checks if the values of the operands are monotonically decreasing.
string> string-greaterp Checks if the values of the operands are monotonically increasing.
string<= string-not-greaterp Checks if the value of any left operand is greater than or equal to the value of next right operand, if yes then condition becomes true.
string>= string-not-lessp Checks if the value of any left operand is less than or equal to the value of its right operand, if yes then condition becomes true.

例

创建一个名为main.lisp的新源代码文件，然后在其中键入以下代码。

现场演示
; case-sensitive comparison
(write (string= "this is test" "This is test"))
(terpri)
(write (string> "this is test" "This is test"))
(terpri)
(write (string< "this is test" "This is test"))
(terpri)

;case-insensitive comparision
(write (string-equal "this is test" "This is test"))
(terpri)
(write (string-greaterp "this is test" "This is test"))
(terpri)
(write (string-lessp "this is test" "This is test"))
(terpri)

;checking non-equal
(write (string/= "this is test" "this is Test"))
(terpri)
(write (string-not-equal "this is test" "This is test"))
(terpri)
(write (string/= "lisp" "lisping"))
(terpri)
(write (string/= "decent" "decency"))

当您执行代码时，它返回以下结果-

NIL
0
NIL
T
NIL
NIL
8
NIL
4
5

案例控制功能

下表描述了案例控制功能-

Sr.No. Function & Description
1

string-upcase

Converts the string to upper case
2

string-downcase

Converts the string to lower case
3

string-capitalize

Capitalizes each word in the string

例

创建一个名为main.lisp的新源代码文件，然后在其中键入以下代码。

现场演示
(write-line (string-upcase "a big hello from tutorials point"))
(write-line (string-capitalize "a big hello from tutorials point"))

当您执行代码时，它返回以下结果-

A BIG HELLO FROM TUTORIALS POINT
A Big Hello From Tutorials Point

修整弦

下表描述了字符串修剪功能-

Sr.No. Function & Description
1

string-trim

It takes a string of character(s) as first argument and a string as the second argument and returns a substring where all characters that are in the first argument are removed off the argument string.
2

String-left-trim

It takes a string of character(s) as first argument and a string as the second argument and returns a substring where all characters that are in the first argument are removed off the beginning of the argument string.
3

String-right-trim

It takes a string character(s) as first argument and a string as the second argument and returns a substring where all characters that are in the first argument are removed off the end of the argument string.

例

创建一个名为main.lisp的新源代码文件，然后在其中键入以下代码。

现场演示
(write-line (string-trim " " "   a big hello from tutorials point   "))
(write-line (string-left-trim " " "   a big hello from tutorials point   "))
(write-line (string-right-trim " " "   a big hello from tutorials point   "))
(write-line (string-trim " a" "   a big hello from tutorials point   "))

当您执行代码时，它返回以下结果-

a big hello from tutorials point
a big hello from tutorials point   
   a big hello from tutorials point
big hello from tutorials point

其他字符串函数

LISP中的字符串是数组，因此也是序列。我们将在以后的教程中介绍这些数据类型。适用于数组和序列的所有函数也适用于字符串。但是，我们将使用各种示例来演示一些常用功能。

计算长度

长度函数计算字符串的长度。

提取子串

subseq函数返回一个子字符串(因为字符串也是一个序列)，该子字符串从特定的索引开始，一直到特定的结束索引或字符串。

在一个字符串访问一个字符

char函数允许访问字符串的各个字符。

例

创建一个名为main.lisp的新源代码文件，然后在其中键入以下代码。

现场演示
(write (length "Hello World"))
(terpri)
(write-line (subseq "Hello World" 6))
(write (char "Hello World" 6))

当您执行代码时，它返回以下结果-

11
World
#\W

字符串的排序和合并

sort函数允许对字符串进行排序。它接受一个序列(向量或字符串)和一个两个参数的谓词，并返回该序列的排序版本。

合并函数接受两个序列和一个谓词，并根据该谓词返回通过合并两个序列而产生的序列。

例

创建一个名为main.lisp的新源代码文件，然后在其中键入以下代码。

现场演示
;sorting the strings
(write (sort (vector "Amal" "Akbar" "Anthony") #'string

当您执行代码时，它返回以下结果-

#("Akbar" "Amal" "Anthony")
#("Anju" "Anuj" "Avni" "Rishi" "Zara" "Priyanka")

反转字符串

反向函数反转字符串。

例如，创建一个名为main.lisp的新源代码文件，然后在其中键入以下代码。

现场演示
(write-line (reverse "Are we not drawn onward, we few, drawn onward to new era"))

当您执行代码时，它返回以下结果-

are wen ot drawno nward ,wef ew ,drawno nward ton ew erA

连接字符串

串联函数串联两个字符串。这是通用序列函数，您必须提供结果类型作为第一个参数。

例如，创建一个名为main.lisp的新源代码文件，然后在其中键入以下代码。

现场演示
(write-line (concatenate 'string "Are we not drawn onward, " "we few, drawn onward to new era"))

当您执行代码时，它返回以下结果-

Are we not drawn onward, we few, drawn onward to new era