Arduino - 字元函式
所有資料都以字元形式輸入計算機，包括字母、數字和各種特殊符號。在本節中，我們將討論用於檢查和操作單個字元的 C++的函式。
字元處理庫包括幾個執行有用的測試和字元資料操作的函式。每個函式接收一個字元(型別為 int)，或 EOF 作為引數。字元通常被當作整數來操作。
請記住，EOF 通常具有值-1，並且某些硬體體系結構不允許將負值儲存在 char 變數中。因此，字元處理函式將字元操作為整數。
下表總結了字元處理庫的功能。使用字元處理庫中的函式時，請包含 <cctype> 標頭。
例子
以下示例演示了函式 isdigit，isalpha，isalnum 和 isxdigit 的使用。函式 isdigit 確定其引數是否為數字（0-9）。函式 isalpha 確定其引數是大寫字母（AZ）還是小寫字母（a-z）。函式 isalnum 確定其引數是大寫，小寫字母還是數字。函式 isxdigit 確定其引數是否為十六進位制數字（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
我們對每個函式使用條件運算子 ?: 來確定在輸出中應該列印字串 is a 還是字串 is not a。例如，行 a 表示如果'8’是數字 - 即，如果 isdigit 返回真（非零）值 - 則列印字串 8 is a 。如果'8’不是數字（即，如果 isdigit 返回 0），則列印字串 8 is not a 。
例 2
以下示例演示了函式 islower 和 isupper 的使用。函式 islower 確定其引數是否為小寫字母（a-z）。函式 isupper 確定其引數是否為大寫字母（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
以下示例演示了函式 isspace，iscntrl，ispunct，isprint 和 isgraph 的使用。
-
函式 isspace 確定其引數是否為空格字元，例如空格（’ ‘），換頁符（’\f’），換行符（’\n’），回車符（’\r’），水平製表符（’\t’）或垂直製表符（’\v’）。
-
函式 iscntrl 確定其引數是否為控制字元，如水平製表符（’\t’），垂直製表符（’\v’），換頁符（’\f’），警告（’\ a’），退格鍵（’\ b’），回車符（’\r’）或換行符（’\n’）。
-
函式 ispunct 確定其引數是否是空格，數字或字母以外的列印字元，例如
$ # ( ) [ ] { } ; : %。 -
函式 isprint 確定其引數是否是可以在螢幕上顯示的字元（包括空格字元）。
-
函式 isgraph 測試與 isprint 相同的字元，但不包括空格字元。
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