Arduino - 字符函数
所有数据都以字符形式输入计算机，包括字母、数字和各种特殊符号。在本节中，我们将讨论用于检查和操作单个字符的 C++的函数。
字符处理库包括几个执行有用的测试和字符数据操作的函数。每个函数接收一个字符(类型为 int)，或 EOF 作为参数。字符通常被当作整数来操作。
请记住，EOF 通常具有值-1，并且某些硬件体系结构不允许将负值存储在 char 变量中。因此，字符处理函数将字符操作为整数。
下表总结了字符处理库的功能。使用字符处理库中的函数时，请包含 <cctype> 标头。
例子
以下示例演示了函数 isdigit，isalpha，isalnum 和 isxdigit 的使用。函数 isdigit 确定其参数是否为数字（0-9）。函数 isalpha 确定其参数是大写字母（AZ）还是小写字母（a-z）。函数 isalnum 确定其参数是大写，小写字母还是数字。函数 isxdigit 确定其参数是否为十六进制数字（A-F，a-f，0-9）。
例 1
void setup () {
Serial.begin (9600);
Serial.print ("According to isdigit:\r");
Serial.print (isdigit( '8' ) ? "8 is a": "8 is not a");
Serial.print (" digit\r" );
Serial.print (isdigit( '8' ) ?"# is a": "# is not a") ;
Serial.print (" digit\r");
Serial.print ("\rAccording to isalpha:\r" );
Serial.print (isalpha('A' ) ?"A is a": "A is not a");
Serial.print (" letter\r");
Serial.print (isalpha('A' ) ?"b is a": "b is not a");
Serial.print (" letter\r");
Serial.print (isalpha('A') ?"& is a": "& is not a");
Serial.print (" letter\r");
Serial.print (isalpha( 'A' ) ?"4 is a":"4 is not a");
Serial.print (" letter\r");
Serial.print ("\rAccording to isalnum:\r");
Serial.print (isalnum( 'A' ) ?"A is a" : "A is not a" );
Serial.print (" digit or a letter\r" );
Serial.print (isalnum( '8' ) ?"8 is a" : "8 is not a" ) ;
Serial.print (" digit or a letter\r");
Serial.print (isalnum( '#' ) ?"# is a" : "# is not a" );
Serial.print (" digit or a letter\r");
Serial.print ("\rAccording to isxdigit:\r");
Serial.print (isxdigit( 'F' ) ?"F is a" : "F is not a" );
Serial.print (" hexadecimal digit\r" );
Serial.print (isxdigit( 'J' ) ?"J is a" : "J is not a" ) ;
Serial.print (" hexadecimal digit\r" );
Serial.print (isxdigit( '7' ) ?"7 is a" : "7 is not a" ) ;
Serial.print (" hexadecimal digit\r" );
Serial.print (isxdigit( '$' ) ? "$ is a" : "$ is not a" );
Serial.print (" hexadecimal digit\r" );
Serial.print (isxdigit( 'f' ) ? “f is a" : "f is not a");
}
void loop () {
}
结果
According to isdigit:
8 is a digit
According to isalpha:
A is a letter
b is a letter
& is not a letter
4 is not a letter
According to isalnum:
A is a digit or a letter
8 is a digit or a letter
According to isxdigit:
F is a hexadecimal digit
J is not a hexadecimal digit
7 is a hexadecimal digit
$ is not a hexadecimal digit
f is a hexadecimal digit
我们对每个函数使用条件运算符 ?: 来确定在输出中应该打印字符串 is a 还是字符串 is not a。例如，行 a 表示如果'8’是数字 - 即，如果 isdigit 返回真（非零）值 - 则打印字符串 8 is a 。如果'8’不是数字（即，如果 isdigit 返回 0），则打印字符串 8 is not a 。
例 2
以下示例演示了函数 islower 和 isupper 的使用。函数 islower 确定其参数是否为小写字母（a-z）。函数 isupper 确定其参数是否为大写字母（A-Z）。
int thisChar = 0xA0;
void setup () {
Serial.begin (9600);
Serial.print ("According to islower:\r") ;
Serial.print (islower( 'p' ) ? "p is a" : "p is not a" );
Serial.print ( " lowercase letter\r" );
Serial.print ( islower( 'P') ? "P is a" : "P is not a") ;
Serial.print ("lowercase letter\r");
Serial.print (islower( '5' ) ? "5 is a" : "5 is not a" );
Serial.print ( " lowercase letter\r" );
Serial.print ( islower( '!' )? "! is a" : "! is not a") ;
Serial.print ("lowercase letter\r");
Serial.print ("\rAccording to isupper:\r") ;
Serial.print (isupper ( 'D' ) ? "D is a" : "D is not an" );
Serial.print ( " uppercase letter\r" );
Serial.print ( isupper ( 'd' )? "d is a" : "d is not an") ;
Serial.print ( " uppercase letter\r" );
Serial.print (isupper ( '8' ) ? "8 is a" : "8 is not an" );
Serial.print ( " uppercase letter\r" );
Serial.print ( islower( '$' )? "$ is a" : "$ is not an") ;
Serial.print ("uppercase letter\r ");
}
void setup () {
}
结果
According to islower:
p is a lowercase letter
P is not a lowercase letter
5 is not a lowercase letter
! is not a lowercase letter
According to isupper:
D is an uppercase letter
d is not an uppercase letter
8 is not an uppercase letter
$ is not an uppercase letter
例 3
以下示例演示了函数 isspace，iscntrl，ispunct，isprint 和 isgraph 的使用。
-
函数 isspace 确定其参数是否为空格字符，例如空格（’ ‘），换页符（’\f’），换行符（’\n’），回车符（’\r’），水平制表符（’\t’）或垂直制表符（’\v’）。
-
函数 iscntrl 确定其参数是否为控制字符，如水平制表符（’\t’），垂直制表符（’\v’），换页符（’\f’），警告（’\ a’），退格键（’\ b’），回车符（’\r’）或换行符（’\n’）。
-
函数 ispunct 确定其参数是否是空格，数字或字母以外的打印字符，例如
$ # ( ) [ ] { } ; : %。 -
函数 isprint 确定其参数是否是可以在屏幕上显示的字符（包括空格字符）。
-
函数 isgraph 测试与 isprint 相同的字符，但不包括空格字符。
void setup () {
Serial.begin (9600);
Serial.print ( " According to isspace:\rNewline ") ;
Serial.print (isspace( '\n' )? " is a" : " is not a" );
Serial.print ( " whitespace character\rHorizontal tab") ;
Serial.print (isspace( '\t' )? " is a" : " is not a" );
Serial.print ( " whitespace character\n") ;
Serial.print (isspace('%')? " % is a" : " % is not a" );
Serial.print ( " \rAccording to iscntrl:\rNewline") ;
Serial.print ( iscntrl( '\n' )?"is a" : " is not a" ) ;
Serial.print (" control character\r");
Serial.print (iscntrl( '$' ) ? " $ is a" : " $ is not a" );
Serial.print (" control character\r");
Serial.print ("\rAccording to ispunct:\r");
Serial.print (ispunct(';' ) ?"; is a" : "; is not a" ) ;
Serial.print (" punctuation character\r");
Serial.print (ispunct('Y' ) ?"Y is a" : "Y is not a" ) ;
Serial.print ("punctuation character\r");
Serial.print (ispunct('#' ) ?"# is a" : "# is not a" ) ;
Serial.print ("punctuation character\r");
Serial.print ( "\r According to isprint:\r");
Serial.print (isprint('$' ) ?"$ is a" : "$ is not a" );
Serial.print (" printing character\rAlert ");
Serial.print (isprint('\a' ) ?" is a" : " is not a" );
Serial.print (" printing character\rSpace ");
Serial.print (isprint(' ' ) ?" is a" : " is not a" );
Serial.print (" printing character\r");
Serial.print ("\r According to isgraph:\r");
Serial.print (isgraph ('Q' ) ?"Q is a" : "Q is not a" );
Serial.print ("printing character other than a space\rSpace ");
Serial.print (isgraph (' ') ?" is a" : " is not a" );
Serial.print ("printing character other than a space ");
}
void loop () {
}
结果
According to isspace:
Newline is a whitespace character
Horizontal tab is a whitespace character
% is not a whitespace character
According to iscntrl:
Newline is a control character
$ is not a control character
According to ispunct:
; is a punctuation character
Y is not a punctuation character
According to isprint:
$ is a printing character
Alert is not a printing character
Space is a printing character
According to isgraph:
Q is a printing character other than a space
Space is not a printing character other than a space