使用函数库中指定的函数，可以在C++中进行字符分类。本文讨论了许多用于对字符进行分类的函数。
1. isalpha()：如果字符是字母，则此函数返回true，否则返回false。根据此函数， az和AZ中的所有字符返回true。
2. isalnum()：如果字符是字母或数字，则此函数返回true，否则返回false。根据此函数，来自az，AZ的所有字符以及所有数字均返回true。
3. isdigit()：如果字符是数字，则此函数返回true，否则返回false。根据此函数，所有数字均返回true。
// C++ program to demonstrate insalpha(), isnum()
// and isdigit()
#include
#include
using namespace std;
int main()
{
// initializing character array
char ch[5] = "g1";
// checking for isalpha() function
for (int i=0; i<2; i++)
{
if (isalpha(ch[i]))
cout << ch[i] << " is alphabet" << endl;
else
cout << ch[i] << " is not alphabet" << endl;
}
cout << endl;
// checking for isalnum() function
for (int i=0; i<2; i++)
{
if (isalnum(ch[i]))
cout << ch[i] << " is alphanumeric" << endl;
else
cout << ch[i] << " is not alphanumeric" << endl;
}
cout << endl;
// checking for isdigit() function
for (int i=0; i<2; i++)
{
if (isdigit(ch[i]))
cout << ch[i] << " is digit" << endl;
else
cout << ch[i] << " is not digit" << endl;
}
}
输出 ：
g is alphabet
1 is not alphabet
g is alphanumeric
1 is alphanumeric
g is not digit
1 is digit
4. isblank()：如果字符是空格或制表符，则此函数返回true，否则返回false。
5. isspace()：如果字符是空格或制表符或空白控制代码(例如\ n，\ r)，则此函数返回true，否则返回false。
6. iscntrl()：如果字符是制表符或任何控制代码，则此函数返回true，否则返回false。
// C++ program to demonstrate iscntrl(), isblank() and
// isspace()
#include
#include
using namespace std;
int main()
{
// initializing character array
char ch[4] = " \n\t";
// checking for iscntrl() function
for (int i=0; i<3; i++)
{
if (iscntrl(ch[i]))
cout << " Character is control code " << endl;
else
cout << " Character is not control code" << endl;
}
cout << endl;
// checking for isblank() function
for (int i=0; i<3; i++)
{
if (isblank(ch[i]))
cout << " Character is blank" << endl;
else
cout << " Character is not blank" << endl;
}
cout << endl;
// checking for isspace() function
for (int i=0; i<3; i++)
{
if (isspace(ch[i]))
cout << " Character is space" << endl;
else
cout << " Character is not space" << endl;
}
}
输出 ：
Character is not control code
Character is control code
Character is control code
Character is blank
Character is not blank
Character is blank
Character is space
Character is space
Character is space
7. isprint()：如果字符可以在控制台上打印，则此函数返回true，即除控制代码外的所有其他字符返回false。
8. isxdigit()：如果字符为十六进制(即0-9)，则此函数返回true，否则返回false。
9. ispunct()：如果字符是标点符号，则此函数返回true，否则返回false。
// C++ program to demonstrate isprint(), isxdigit() and
// ispunct()
#include
#include
using namespace std;
int main()
{
// initializing character array
char ch[6] = "\t@gf1";
// checking for isprint() function
for (int i=0; i<5; i++)
{
if (isprint(ch[i]))
cout << ch[i] << " is printable character " << endl;
else
cout << ch[i] << " is not printable Character" << endl;
}
cout << endl;
// checking for isxdigit() function
for (int i=0; i<5; i++)
{
if (isxdigit(ch[i]))
cout << ch[i] << " is hexadecimal Character" << endl;
else
cout << ch[i] << " is not hexadecimal Character" << endl;
}
cout << endl;
// checking for ispunct() function
for (int i=0; i<5; i++)
{
if (ispunct(ch[i]))
cout << ch[i] << " is punctuation mark" << endl;
else
cout << ch[i] << " is not punctuation mark" << endl;
}
}
输出 ：
is not printable Character
@ is printable character
g is printable character
f is printable character
1 is printable character
is not hexadecimal Character
@ is not hexadecimal Character
g is not hexadecimal Character
f is hexadecimal Character
1 is hexadecimal Character
is not punctuation mark
@ is punctuation mark
g is not punctuation mark
f is not punctuation mark
1 is not punctuation mark
参考：http://www.cplusplus.com/reference/cctype/
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