Arduino - 字符函数

所有数据均以字符形式输入到计算机中，包括字母、数字和各种特殊符号。在本部分中，我们讨论 C++ 的能力，以便检查和操作单个字符。

字符处理库包括执行字符数据有用的测试和操作的多个函数。每个函数接收一个字符（表示为 int）或 EOF 作为参数。字符常常像整数一样进行操作。

记住，EOF 通常具有值 -1，而且一些硬件体系结构不允许在字符变量中存储负值。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函数。当使用字符处理库中的函数时，请包含头文件 <cctype>。

示例

以下示例演示了函数 isdigit、isalpha、isalnum 和 isxdigit 的用法。函数 isdigit 确定其参数是否是数字 (0–9)。函数 isalpha 确定其参数是否是大小写字母 (A-Z) 或小写字母 (a–z)。函数 isalnum 确定其参数是否是大小写字母或数字。函数 isxdigit 确定其参数是否是十六进制数字 (A–F、a–f 和 0–9)。

示例 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
# 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 (?:) 以确定对于每个测试的字符，是否应在输出中打印字符串“ 是”或“ 不是”。例如，行 a 指示：如果 '8' 是一个数字（即，如果 isdigit 返回一个真（非零）值），则打印字符串“8 是”。如果 '8' 不是一个数字（即，如果 isdigit 返回 0），则打印字符串“ 8 不是”。

示例 2

以下示例演示了函数 islower 和 isupper 的用法。函数 islower 确定其参数是否是小写字母 (a–z)。函数 isupper 确定其参数是否是大小写字母 (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

示例 3

以下示例演示了函数 isspace、iscntrl、ispunct、isprint 和 isgraph 的用法。

• 函数 isspace 确定其参数是否是空白字符，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 确定其参数是否是控件字符，例如水平制表符 ('\t')、垂直制表符 ('\v')、换页符 ('\f')、警报符 ('\a')、退格符 ('\b')、回车符 ('\r') 或换行符 ('\n')。

• 函数 ispunct 确定其参数是否是除空格、数字或字母之外的可打印字符，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

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