Arduino - 字符函数（ Character Functions）

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 ++的功能。

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，表示为int，或EOF作为参数。 字符通常被操作为整数。

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 (Examples)

以下示例演示了函数isdigit, isalpha, isalnum和isxdigit 。 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）。

例子1 (Example 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");
   <!--Serial.print (" hexadecimal digit\r" );-->
}
void loop () {
}

结果 (Result)

According to isdigit:
8 is a digit
# is not 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
# is not 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(?:)来确定字符串“是a”还是字符串“不是a”应该在输出中打印每个测试的字符。 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是a”。 如果'8'不是数字（即，如果isdigit返回0），则打印字符串“8不是a”。

例子2 (Example 2)

以下示例演示了函数islower和isupper 。 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 (Result)

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

例子3 (Example 3)

以下示例演示了函数isspace, iscntrl, ispunct, isprint和isgraph 。

• 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$，＃，（，），[，]，{，} ,;，或％。

• 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 (Result)

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
# is 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