Arduino 字符函数

由 drbear 创建，youj 最后一次修改 2016-12-26 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<cctype>标题。序号原型和描述1 int isdigit(int c)如果c是数字，则返回1，否则返回0。2 int isalpha(int c)如果c是字母，则返回1，否则返回0。3 int isalnum(int c)如果c是数字或字母，则返回1，否则返回0。4 int isxdigit(int c)如果c是十六进制数字字符，则返回1，否则返回0。5 int islower(int c)如果c是小写字母，则返回1，否则返回0。6 int isupper(int c)如果c是大写字母，则返回1；否则返回0。7 int isspace(int c)如果c是空白字符：换行符（'\n'）、空格符（' '）、换页符（'\f'）、回车符（'\r'）、水平制表符（'\t'）或垂直制表符（'\v'），则返回1，否则返回0。8 int iscntrl(int c)如果c是控制字符，如换行符（'\n'）、换页符（'\f'）、回车符（'\r'）、水平制表符 （\v'）、垂直制表符（'\v'）、alert（'\a'）或退格（'\b'），则返回1，否则返回0。9 int ispunct(int c)如果c是除空格，数字或字母以外的打印字符，则返回1，否则返回0。10 int isprint(int c)如果c是包含空格（' '）的打印字符，则返回1，否则返回0。11 int isgraph(int c)如果c是除空格（' '）之外的打印字符，则返回1，否则返回0。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1void 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 digitAccording to isalpha:A is a letterb is a letter& is not a letter4 is not a letterAccording to isalnum:A is a digit or a letter8 is a digit or a letter# is not a digit or a letterAccording to isxdigit:F is a hexadecimal digitJ is not a hexadecimal digit7 is a hexadecimal digit$ is not a hexadecimal digitf 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 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 letterP is not a lowercase letter5 is not a lowercase letter! is not a lowercase letterAccording to isupper