Common Linux C functions-character Testing

Common Linux C functions-character testing-general Linux technology-Linux programming and kernel information. For more information, see the following section. Isalnum (test whether the character is English or a number)
Related functions: isalpha, isdigit, islower, and isupper

Header file # include

Defines the int isalnum (int c) function)

Function Description checks whether parameter c is an English letter or Arabic number. In Standard c, it is equivalent to using "isalpha (c) | isdigit (c)" for testing.

Returns TRUE if parameter c is a letter or number; otherwise, returns NULL (0 ).

This is a macro definition, not a real function.

Example/* Find the characters in the str string that are English letters or numbers */
# Include <ctype. h>
Main ()
{
Char str [] = "123c @ # FDsP [e ?";
Int I;
For (I = 0; str! = 0; I ++)
If (isalnum (str) printf ("% c is an alphanumeric character \ n", str );
}

Run 1 is an apphabetic character
2 is an apphabetic character
3 is an apphabetic character
C is an apphabetic character
F is an apphabetic character
D is an apphabetic character
S is an apphabetic character
P is an apphabetic character
E is an apphabetic character

　




Isalpha (test whether the character is an English letter)
Related functions: isalnum, islower, isupper

Header file # include

Defines the int isalpha (int c) function)

Function Description checks whether the parameter c is an English letter. In Standard c, it is equivalent to using "isupper (c) | islower (c)" for testing.

Returns TRUE if parameter c is an English letter; otherwise, returns NULL (0 ).

This is a macro definition, not a real function.

Example/* Find the characters in the str string that are English letters */
# Include
Main ()
{
Char str [] = "123c @ # FDsP [e ?";
Int I;
For (I = 0; str! = 0; I ++)
If (isalpha (str) printf ("% c is an alphanumeric character \ n", str );
}

Execute c is an apphabetic character
F is an apphabetic character
D is an apphabetic character
S is an apphabetic character
P is an apphabetic character
E is an apphabetic character

　




Isascii (test whether the character is an ASCII character)
Iscntrl

Header file # include

Defines the int isascii (int c) function );

Function Description checks whether the parameter c is an ASCII character, that is, whether the range of c is between 0 and 127.

Returns TRUE if the parameter c is an ASCII character; otherwise, returns NULL (0 ).

This is a macro definition, not a real function.

Example/* determine whether int I has an ASCII character mapped */
# Include
Main ()
{
Int I;
For (I = 125; I <130; I ++)
If (isascii (I ))
Printf ("% d is an ascii character: % c \ n", I, I );
Else
Printf ("% d is not an ascii character \ n", I );
}

Run 125 is an ascii character :}
126 is an ascii character :~
127 is an ascii character:
128 is not an ascii character
129 is not an ascii character

　




Iscntrl (test whether the character is an ASCII control character)
Isascii

Header file # include

Defines the int iscntrl (int c) function );

Function Description checks whether the parameter c is an ASCII control code, that is, whether the range of c is between 0 and 30.

If the return value is an ASCII control code, TRUE is returned. Otherwise, NULL (0) is returned ).

This is a macro definition, not a real function.

　




Isdigit (test whether the character is Arabic numerals)
Isxdigit

Header file # include

Defines the int isdigit (int c) function)

Function Description: Check whether the value of parameter c is 0 to 9.

If the return value is an Arabic number, TRUE is returned. Otherwise, NULL (0) is returned ).

This is a macro definition, not a real function.

Example/* Find the characters in the str string that are Arabic numerals */
# Include
Main ()
{
Char str [] = "123 @ # FDsP [e? ";
Int I;
For (I = 0; str! = 0; I ++)
If (isdigit (str) printf ("% c is an digit character \ n", str );
}

Execute 1 is an digit character
2 is an digit character
3 is an digit character

　




Isgraphis (test whether the character is printable)
Isprint

Header file # include

Defines the int isgraph (int c) function)

Function Description checks whether parameter c is printable. If the ASCII code mapped to c is printable, TRUE is returned if it is not a space character.

Returns TRUE if parameter c is printable; otherwise, returns NULL (0 ).

This is a macro definition, not a real function.

Example/* determine which of the str strings are printable characters */
# Include
Main ()
{
Char str [] = "a5 @;";
Int I;
For (I = 0; str! = 0; I ++)
If (isgraph (str) printf ("str [% d] is printable character: % d \ n", I, str );
}

Run str [0] is printable character:
Str [1] is printable character: 5
Str [3] is printable character :@
Str [4] is printable character :;

　




Islower (test whether the character is a lowercase letter)
Isalpha, isupper

Header file # include

Int islower (int c)

Function Description checks whether parameter c is a lowercase English letter.

If the return value is a lowercase English letter, TRUE is returned. Otherwise, NULL (0) is returned ).

This is a macro definition, not a real function.

Example # include
Main ()
{
Char str [] = "123 @ # FDsP [e? ";
Int I;
For (I = 0; str! = 0; I ++)
If (islower (str) printf ("% c is a lower-case character \ n", str );
}

Execute c is a lower-case character
S is a lower-case character
E is a lower-case character

　




Isprint (test character is (no is printable)
Isgraph

Header file # include

Defines the int isprint (int c) function );

Function Description checks whether parameter c is printable. If the ASCII code mapped to c is printable and contains space characters, TRUE is returned.

Returns TRUE if parameter c is printable; otherwise, returns NULL (0 ).

This is a macro definition, not a real function.

Example/* determine which of the str strings contain printable characters */
# Include
Main ()
{
Char str [] = "a5 @;";
Int I;
For (I = 0; str! = 0; I ++)
If (isprint (str) printf ("str [% d] is printable character: % d \ n", I, str );
}

Run str [0] is printable character:
Str [1] is printable character: 5
Str [2] is printable character:
Str [3] is printable character :@
Str [4] is printable character :;

　




Isspace (test whether the character is a space character)
Isgraph

Header file # include

Defines the int isspace (int c) function)

Function Description checks whether parameter c is a space character, that is, whether it is a space (''), a positioning character ('\ t'), or a CR (' \ R '), line feed ('\ n'), vertical positioning character (' \ V'), or flip ('\ F.

Returns TRUE if parameter c is a space character; otherwise, returns NULL (0 ).

This is a macro definition, not a real function.

Example/* find the space characters contained in the string str [] and display the ASCII code of the space characters */
# Include
Main ()
{
Char str = "123c @ # FD \ tsP [e? \ N ";
Int I;
For (I = 0; str! = 0; I ++)
If (isspace (str ))
Printf ("str [% d] is a white-space character: % d \ n", I, str );
}

Run str [4] is a white-space character: 32
Str [7] is a white-space character: 32
Str [10] is a white-space character: 9/* \ t */
Str [16] is a white-space character: 10/* \ t */

　




Ispunct (test whether the character is a punctuation or special symbol)
Related functions: isspace, isdigit, and isalpha

Header file # inlude

Int ispunct (int c)

Function Description checks whether parameter c is a punctuation or special symbol. TRUE indicates that parameter c is a non-space, non-digit, and non-English letter.

Return Value v if the parameter c is a punctuation or special symbol, TRUE is returned; otherwise, NULL (0) is returned ).

This is a macro definition, not a real function.

Example/* List punctuation marks or special characters in string str */
# Include
Main ()
{
Char str [] = "123c @ # FDsP [e? ";
Int I;
For (I = 0; str! = 0; I ++)
If (ispunct (str) printf ("% c \ n", str );
}

Run v
@#[?

　




Isupper (test whether the character is an uppercase English letter)
Related functions: isalpha and islower

Header file # include

Defines the int isupper (int c) function)

Function Description checks whether parameter c is an uppercase English letter.

Returns TRUE if parameter c is an uppercase English letter; otherwise, returns NULL (0 ).

This is a macro definition, not a real function.

Example/* Find the characters in str that are uppercase letters */
# Include
Main ()
{
Char str [] = "123c @ # FDsP [e? ";
Int I;
For (I = 0; str! = 0; I ++)
If (isupper (str) printf ("% c is an uppercase character \ n", str );
}

Execute F is an uppercase character
D is an uppercase character
P is an uppercase character

　




Isxdigit (test whether the character is a hexadecimal number)
Isalnum, isdigit

Header file # include

Defines the int isxdigit (int c) function)

Function Description checks whether the parameter c is a hexadecimal number. If c is one of the following, TRUE is returned. Hexadecimal number: 0123456789 ABCDEF.

If the return value is a hexadecimal number, TRUE is returned. Otherwise, NULL (0) is returned ).

This is a macro definition, not a real function.

Example/* Find the character string str is a hexadecimal number */
# Include
Main ()
{
Char str [] = "123c @ # FDsP [e? ";
Int I;
For (I = 0; str! = 0; I ++)
If (isxdigit (str) printf ("% c is a hexadecimal digits \ n", str );
}

Execute 1 is a hexadecimal digits
2 is a hexadecimal digits
3 is a hexadecimal digits
C is a hexadecimal digits
F is a hexadecimal digits
D is a hexadecimal digits
E is a hexadecimal digits