cmake string的所有用法， 并给出示例

CMake中的string命令用于操作字符串，其语法为：

string(<COMMAND> [args...])

其中，`<COMMAND>`表示要执行的操作，`[args...]`则表示操作所需的参数。

下面是string命令的所有用法及示例：

1. `LENGTH`：返回字符串的长度

string(LENGTH "hello world" my_length)
message("Length of string is ${my_length}")

输出：

Length of string is 11

2. `SUBSTRING`：截取子字符串

string(SUBSTRING "hello world" 0 5 my_substring)
message("Substring is ${my_substring}")

输出：

Substring is hello

3. `REPLACE`：替换字符串中的子字符串

string(REPLACE "world" "CMake" my_replaced_string "hello world")
message("Replaced string is ${my_replaced_string}")

输出：

Replaced string is hello CMake

4. `FIND`：查找字符串中的子字符串

string(FIND "hello world" "world" my_position)
message("Position of substring is ${my_position}")

输出：

Position of substring is 6

5. `TOLOWER`：将字符串转换为小写

string(TOLOWER "HeLLo WoRLd" my_lowercase_string)
message("Lowercase string is ${my_lowercase_string}")

输出：

Lowercase string is hello world

6. `TOUPPER`：将字符串转换为大写

string(TOUPPER "HeLLo WoRLd" my_uppercase_string)
message("Uppercase string is ${my_uppercase_string}")

输出：

Uppercase string is HELLO WORLD

7. `COMPARE`：比较两个字符串

string(COMPARE EQUAL "hello" "hello" my_equal)
message("Strings are equal: ${my_equal}")
string(COMPARE EQUAL "hello" "world" my_equal)
message("Strings are equal: ${my_equal}")

输出：

Strings are equal: TRUE
Strings are equal: FALSE

8. `MATCH`：匹配正则表达式

string(MATCH "hello" "hello world" my_match)
message("Matched string is ${my_match}")

输出：

Matched string is hello

9. `REGEX`：正则表达式替换

string(REGEX REPLACE "world" "CMake" my_replaced_string "hello world")
message("Replaced string is ${my_replaced_string}")

输出：

Replaced string is hello CMake

10. `ASCII`：获取字符的ASCII码值

string(ASCII "a" my_ascii_value)
message("ASCII value is ${my_ascii_value}")

输出：

ASCII value is 97

11. `CONFIGURE`：在字符串中进行配置

set(my_string "Hello ${CMAKE_PROJECT_NAME}!")
string(CONFIGURE "${my_string}" my_configured_string)
message("Configured string is ${my_configured_string}")

输出：

Configured string is Hello <project-name>!

其中，`<project-name>`会被替换为实际的项目名称。