Arduino 字符函數(shù)

所有數(shù)據(jù)都以字符形式輸入計算機，包括字母，數(shù)字和各種特殊符號。在本章節(jié)中，我們討論C++檢查和操作單個字符的功能。

字符處理庫包括幾個函數(shù)，執(zhí)行有用的測試和字符數(shù)據(jù)的操作。每個函數(shù)接收一個字符，表示為int或EOF作為參數(shù)。字符通常作為整數(shù)操作。

記住，EOF通常具有值-1，而一些硬件架構(gòu)不允許負(fù)值存儲在char變量中。因此，字符處理函數(shù)將字符作為整數(shù)來操作。

下表總結(jié)了字符處理庫的函數(shù)。使用字符處理庫中的函數(shù)時，請包含<cctype>標(biāo)題。

例子

以下示例演示如何使用函數(shù) isdigit，isalpha，isalnum 和 isxdigit 。函數(shù) isdigit 確定其參數(shù)是否為數(shù)字（0-9）。函數(shù) isalpha 確定其參數(shù)是大寫字母（A-Z）還是小寫字母（a-z）。函數(shù) isalnum 確定其參數(shù)是大寫，小寫字母還是數(shù)字。函數(shù) isxdigit 確定其參數(shù)是否為十六進制數(shù)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 () {

}

結(jié)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

我們對每個函數(shù)使用條件運算符（?:）來確定字符串“is a”或字符串“is not a”是否應(yīng)該打印在每個測試字符的輸出中。例如，行a表示如果“8”是數(shù)字，即如果isdigit返回真（非零）值，則打印字符串“8 is a”。如果“8”不是數(shù)字（即，如果isdigit返回0），則打印字符串“8 is not a”。

例2

以下示例演示了函數(shù) islower 和 isupper 的使用。函數(shù) islower 確定其參數(shù)是否為小寫字母（a-z）。函數(shù) isupper 確定其參數(shù)是否為大寫字母（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 () {

}

結(jié)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數(shù) isspace，iscntrl，ispunct，isprint 和 isgraph 。

• 函數(shù) isspace 確定其參數(shù)是否為空白字符，例如空格（' '），換頁符（'\f'），換行符（'\n'），回車符（'\r'），水平制表符（'\t'）或垂直制表符（'\v'）。

• 函數(shù) iscntrl 確定其參數(shù)是否為控制字符，如水平制表符（'\t'），垂直制表符（'\v'），換頁符（'\f'），alert（'\a'），退格符（'\b'），回車符（'\r'）或換行符（'\n'）。

• 函數(shù) ispunct 確定其參數(shù)是否是除空格，數(shù)字或字母以外的打印字符（例如$，＃，（，），[，]，{，}，;，：或％）。

• 函數(shù) isprint 確定其參數(shù)是否為可以在屏幕上顯示的字符（包括空格字符）。

• 函數(shù) isgraph 測試與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 () {

}

結(jié)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