2.2 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。在本章节中，我们讨论C++检查和操作单个字符的功能。
字符处理库包括几个函数，执行有用的测试和字符数据的操作。每个函数接收一个字符，表示为int或EOF作为参数。字符通常作为整数操作。
记住，EOF通常具有值-1，而一些硬件架构不允许负值存储在char变量中。因此，字符处理函数将字符作为整数来操作。
下表总结了字符处理库的函数。使用字符处理库中的函数时，请包含标题。
例子
以下示例演示如何使用函数 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（A-Z）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 (" digitr" );
Serial.print (isdigit( '8' ) ?"# is a": "# is not a") ;
Serial.print (" digitr");
Serial.print ("rAccording to isalpha:r" );
Serial.print (isalpha('A' ) ?"A is a": "A is not a");
Serial.print (" letterr");
Serial.print (isalpha('A' ) ?"b is a": "b is not a");
Serial.print (" letterr");
Serial.print (isalpha('A') ?"& is a": "& is not a");
Serial.print (" letterr");
Serial.print (isalpha( 'A' ) ?"4 is a":"4 is not a");
Serial.print (" letterr");
Serial.print ("rAccording to isalnum:r");
Serial.print (isalnum( 'A' ) ?"A is a" : "A is not a" );
Serial.print (" digit or a letterr" );
Serial.print (isalnum( '8' ) ?"8 is a" : "8 is not a" ) ;
Serial.print (" digit or a letterr");
Serial.print (isalnum( '#' ) ?"# is a" : "# is not a" );
Serial.print (" digit or a letterr");
Serial.print ("rAccording to isxdigit:r");
Serial.print (isxdigit( 'F' ) ?"F is a" : "F is not a" );
Serial.print (" hexadecimal digitr" );
Serial.print (isxdigit( 'J' ) ?"J is a" : "J is not a" ) ;
Serial.print (" hexadecimal digitr" );
Serial.print (isxdigit( '7' ) ?"7 is a" : "7 is not a" ) ;
Serial.print (" hexadecimal digitr" );
Serial.print (isxdigit( '$' ) ? "$ is a" : "$ is not a" );
Serial.print (" hexadecimal digitr" );
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（?:）来确定字符串“is a”或字符串“is not a”是否应该打印在每个测试字符的输出中。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 letterr" );
Serial.print ( islower( 'P') ? "P is a" : "P is not a") ;
Serial.print ("lowercase letterr");
Serial.print (islower( '5' ) ? "5 is a" : "5 is not a" );
Serial.print ( " lowercase letterr" );
Serial.print ( islower( '!' )? "! is a" : "! is not a") ;
Serial.print ("lowercase letterr");
Serial.print ("rAccording to isupper:r") ;
Serial.print (isupper ( 'D' ) ? "D is a" : "D is not an" );
Serial.print ( " uppercase letterr" );
Serial.print ( isupper ( 'd' )? "d is a" : "d is not an") ;
Serial.print ( " uppercase letterr" );
Serial.print (isupper ( '8' ) ? "8 is a" : "8 is not an" );
Serial.print ( " uppercase letterr" );
Serial.print ( islower( '$' )? "$ is a" : "$ is not an") ;
Serial.print ("uppercase letterr ");
}
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
以下示例演示如何使用函数 isspace，iscntrl，ispunct，isprint 和 isgraph 。
函数 isspace 确定其参数是否为空白字符，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 确定其参数是否为控制字符，如水平制表符（’t’），垂直制表符（’v’），换页符（’f’），alert（’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，数字或字母以外的打印字符（例如$，＃，（，），[，]，{，}，;，：或％）。
函数 isprint 确定其参数是否为可以在屏幕上显示的字符（包括空格字符）。
函数 isgraph 测试与isprint相同的字符，但不包括空格字符。
void setup () {
Serial.begin (9600);
Serial.print ( " According to isspace:rNewline ") ;
Serial.print (isspace( 'n' )? " is a" : " is not a" );
Serial.print ( " whitespace characterrHorizontal tab") ;
Serial.print (isspace( 't' )? " is a" : " is not a" );
Serial.print ( " whitespace charactern") ;
Serial.print (isspace('%')? " % is a" : " % is not a" );
Serial.print ( " rAccording to iscntrl:rNewline") ;
Serial.print ( iscntrl( 'n' )?"is a" : " is not a" ) ;
Serial.print (" control characterr");
Serial.print (iscntrl( '$' ) ? " $ is a" : " $ is not a" );
Serial.print (" control characterr");
Serial.print ("rAccording to ispunct:r");
Serial.print (ispunct(';' ) ?"; is a" : "; is not a" ) ;
Serial.print (" punctuation characterr");
Serial.print (ispunct('Y' ) ?"Y is a" : "Y is not a" ) ;
Serial.print ("punctuation characterr");
Serial.print (ispunct('#' ) ?"# is a" : "# is not a" ) ;
Serial.print ("punctuation characterr");
Serial.print ( "r According to isprint:r");
Serial.print (isprint('$' ) ?"$ is a" : "$ is not a" );
Serial.print (" printing characterrAlert ");
Serial.print (isprint('a' ) ?" is a" : " is not a" );
Serial.print (" printing characterrSpace ");
Serial.print (isprint(' ' ) ?" is a" : " is not a" );
Serial.print (" printing characterr");
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 spacerSpace ");
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
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