In C++ string is a
null-terminated array of characters. To manipulate strings in C++ we need the
help of string functions and this requires including the header file string.h in order to include function
prototype and definition. To manipulate characters we need to use character
functions and this requires including ctype.h
header file in your program.
Character Functions:
Here by below I am including some of the important character
functions with descriptions:
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Function
|
Description
|
Example
|
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int isalnum(int ch)
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The function isalnum() returns
non-zero if its argument is a letter or a digit. If the character is not an
alphanumeric isalnum() returns 0 (Zero)
|
char ch;
if(isalnum(ch))
cout<<”\n Alphanumeric”;
else
cout<<”\n Non-Alphanumeric”;
|
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int isalpha(int ch)
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The function isalpha() returns
non-zero if ch is a alphabet, else returns zero.
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char ch;
if(isalpha(ch))
cout<<”\n An alphabet”;
else
cout<<”\n No an alphabet”;
|
|
int isdigit(int ch)
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This functions returns non-zero
if ch is a digit (0 – 9) else returns zero.
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char ch;
if(isalpha(ch))
cout<<”\n Is a digit”;
else
cout<<”\n Not a digit”;
|
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int isxdigit(int ch)
|
Tests for hexadecimal
character.
isxdigit is a macro that
classifies ASCII-coded integer values by table lookup. You can make this
macro available as a function by un-defining (#undef) it.
|
int main(void)
{
char ch = 'F';
if (isxdigit(ch))
cout<<ch<<" is a hexidecimal digit";
else
cout<<ch<<"\n is not a hexidecimal digit";
getch();
return 0;
}
Output:
 |
|
int isupper(int ch)
|
Function isupper() returns
non-zero if ch is in upper case; else returns zero.
|
char ch;
if(isupper(ch))
cout<<”\n Is in upper case”;
else
cout<<”\n is in lower case”;
|
|
int islower(int ch)
|
Function islower() returns
non-zero if ch is in lower case; else returns zero.
|
char ch;
if(islower(ch))
cout<<”\n Is in lower case”;
else
cout<<”\n is in upper case”;
|
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int isspace(int c)
|
isspace is a macro that
classifies ASCII-coded integer values by table lookup
|
char ch = ' ';
if (isspace(ch))
cout<<ch<<"is a white space";
else cout<<ch<<"is not white
space\n";
Output:
is a white space
|
|
int toupper(int ch)
|
Function toupper(), return upper
case equivalent to ch; otherwise
keeps the character unchanged.
|
char ch;
cout<<toupper(ch);
|
|
int tolower(int ch)
|
Function tolower(), returns lower
case equivalent to ch; otherwise
keeps the character unchanged.
|
char ch;
cout<<tolower(ch);
|
|
int toascii(int ch)
|
toascii is a
macro that converts the integer c to ASCII by clearing all but the lower 7
bits; this gives a value in the range 0 to 127
|
char ch;int result;
ch ='^';
result = toascii(ch);
cout<<"\n ASCII of
"<<ch<<" = "<<result;
Output:
ASCII of ^ = 94
|
Note** All above mentioned character function uses
ASCII equivalent of the passed character to compare or to convert. That is why
on all above functions passed argument is shown as of type int.
String Functions:
The table given below summarizes
some of the important string functions used in C++. To use these functions you
need to include string.h header file.
String Functions:
The table given below summarizes
some of the important string functions used in C++. To use these functions you
need to include string.h header file.
|
Function
|
Description
|
Example
|
|
char *strcat(char *str1, const char *str2)
|
The function strcat(), concatenates
a copy of str2 to str1 and terminates str1 with a null character. Remember str1 should be large enough to hold
both, its original content and the contents of str2.
|
char *str1="Computer";char *str2="
Science";
strcat(str1,str2);
cout<<str1<<endl;
Output:
Computer Science
|
|
int strcmp(const char *str1, const char *str2)
|
The function strcmp(),
alphabetically compares two strings passed as arguments. It returns –ve value
if str1 is less than str2; 0 if str1 and str2 are
equal; and returns +ve value if str1 is
greater than str2.
|
const char *str1="Abc";
const char *str2="Def";
cout<<strcmp(str1,str2)<<endl;
cout<<strcmp(str2,str1);
Output:
-3
3
|
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char *strcpy(char *str1, const char *str2)
|
Function strcpy(), copies the
content of str2 into str1.
|
char *str1=" ";
const char *str2="C++";
strcpy(str1,str2);
cout<<str1<<endl;
Output:
C++
|
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int strlen(const char *str)
|
Function strlen(), returns the
length of the null-terminated string pointed by str. The null character is not counted.
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const char *str="C++";
cout<<strlen(str)<<endl;
output:
3
|
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char *strrev(char *s)
|
Reverses a string.
strrev() function changes all characters in a string to
reverse order, except the terminating null character
|
int main(void)
{
char *mystr =
"string";
cout<<"Before strrev(): "<<mystr;
strrev(mystr);
cout<<"\nAfter strrev(): "<<mystr;
getch();
return 0;
}
Output:
 |
|
char *strset(char *s, int ch)
|
Sets all characters in a string to
a given character.
strset() function sets all
characters in the string s to the character ch. It quits when the terminating
null character is found.
|
int main(void)
{
char string[10] = "123456789";
char symbol = '*';
cout<<"Before strset(): "<<string;
strset(string, symbol);
cout<<"\nAfter strset(): "<<string;
getch();
return 0;
}
Output:
 |
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