LISP –字符和字符串的比较运算符

使用运算符将字段的内容与另一个字段的内容或常量进行比较。简单来说，运算符用于比较两个或多个不同的值是否相等。

字符：

数字比较函数和运算符（例如 < 和 >）不支持字符。除此之外，使用了 Common LISP 中的两组函数。第一组区分大小写，而第二组不区分大小写或（不区分大小写）。

以下是一些可用于查看两个字符是否相等的比较函数。

Case-Sensitive	Case-Insensitive	Explanation
CHAR=	CHAR-EQUAL	Checks if the operands’ values are all equal; if they are, the condition is true.
CHAR/=	CHAR-NOT-EQUAL	Checks if the operands’ values are all different or not; if they aren’t, the condition is true.
CHAR<	CHAR-LESSP	If the character1 is smaller than character2, the condition is true; otherwise, the condition is false.
CHAR<=	CHAR-NOT-GREATERP	If any of the left character’s values are less than or equal to the value of the following right character, the condition is true.
CHAR>	CHAR-GREATERP	If character1 is greater than character2, the condition is true; otherwise, it is false.
CHAR>=	CHAR-NOT-LESSP	If any left character’s value is more than or equal to its right character’s value, the condition is true.

示例 1：区分大小写的比较

Lisp

(write (CHAR= #\a #\A))
(terpri)
(write (CHAR> #\b #\a))
(terpri)
(write (CHAR< #\A #\a))

输出：运行上述代码时，输出如下。

NIL
T
T

示例 2：不区分大小写的比较

语言

(write (CHAR-EQUAL #\a #\A))
(terpri)
(write (CHAR-EQUAL #\a #\b))
(terpri)
(write (CHAR-LESSP #\a #\b #\c))
(terpri)
(write (CHAR-GREATERP #\a #\b #\c))

输出：运行上述代码时，输出如下。

T
NIL
T
NIL

字符串上的比较运算符：

在 Common Lisp 中，字符串是向量，是一维字符数组。除了双引号字符（“）和转义字符（\）之外，字符集支持的每个字符都可以包含在双引号之间形成一个字符串。和字符一样，字符串也有两组比较运算符，一组区分大小写，另一组不区分大小写。

因此，要检查两个字符串是否相等，下面是一些可以使用的比较函数。

Case-sensitive	Case-insensitive	Explanation
STRING=	STRING-EQUAL	Checks if the operands’ values are all equal; if they are, the condition is true.
STRING/=	STRING-NOT-EQUAL	Checks if the operands’ values are all unequal; if they are, the condition is true.
STRING<	STRING-LESSP	If string1 is smaller than string2, the condition is true; otherwise, the condition is false.
STRING<=	STRING-NOT-GREATERP	If any of the left operands’ values are less than or equal to the value of the following right operand, the condition is true.
STRING>	STRING-GREATERP	If string1 is greater than string2, the condition is true; otherwise, the condition is false.
STRING>=	STRING-NOT-LESSP	If any left operand’s value is more than or equal to its right operand’s value, the condition is true.

示例 1：区分大小写的比较。

语言

(write (STRING= "gfg" "GFG"))
(terpri)
(write (STRING> "gfg" "GFG"))
(terpri)
(write (STRING< "gfg" "GFG"))

输出：运行上述代码时，输出如下。

NIL
0
NIL

示例 2：不区分大小写的比较。

语言

(write (STRING-EQUAL "gfg" "GFG"))
(terpri)
(write (STRING-GREATERP "gfg" "GFG"))
(terpri)
(write (STRING-LESSP "gfg" "GFG"))

输出：比较运算符运行上述代码时，输出如下。

T
NIL
NIL