Miscellaneous String and Character Functions

MISCELLANEOUS STRING AND CHARACTER FUNCTIONS

In this section, we will discuss some character and string manipulation functions that are part of ctype.h, string.h, and stdlib.h.

Character Manipulation Functions

Table 6.2 illustrates some character functions contained in ctype.h.

String Manipulation Functions

In this section we will look at some commonly used string functions present in the string.h header file.

strcat Function

Syntax:

char *strcat (char *strl, const char *str2);

Programming Tip: Before using string copy and concatenating functions, ensure that the destination string has enough space to store all the elements so that memory overwriting does not take place.

The strcat function appends the string pointed to by str2 to the end of the string pointed to by strl. The terminating null character of strl is overwritten. The process stops when the terminating null character of str2 is copied. The argument strl is returned. Note that strl should be big enough to store the contents of str2.

#include <stdio.h>

#include <string.h>

int main()

}

char str1 [50] = "Programming";

char str2 [ ] = "In C";

strcat (str1, str2);

printf("\n str1: %s", str1);

return 0;

}

Output

Str1: Programming In C

strncat Function

Syntax:

char *strncat (char *strl, const char *str2, size_t n);

This function appends the string pointed to by str2 to the end of the string pointed to by str1 up to n characters long. The terminating null character of strl is overwritten. Copying stops when n characters are copied or the terminating null character of str2 is copied. A terminating null character is appended to str1 before returning to the calling function. and

#include <stdio.h>

#include <string.h>

int main()

{

char str1 [50] = "Programming";

char str2 [] = "In C";

strncat (strl, str2, 2);

printf("\n str1: %s", str1);

return 0;

}

Output

strl: Programming In

strchr Function

Syntax:

char *strchr(const char *str, int c);

The strchr() function searches for the first occurrence of the character c (an unsigned char) in the string pointed to by the argument str. The function returns a pointer pointing to the first matching character, or null if no match is found.

#include <stdio.h>

#include <string.h>

int main()

{

char str[50] = "Programming In C";

char *pos;

pos = strchr(str, 'n');

if (pos)

printf("\n n is found in str at position %d", pos);

else

printf("\n n is not present in the string");

return 0;

}

Output

n is found in str at position 9

strrchr Function

Syntax:

char *strrchr (const char *str, int c);

The strrchr() function searches for the first occurrence of the character c (an unsigned char) beginning at the rear end and working towards the front in the string pointed to by the argument str, i.e., the function searches for the last occurrence of the character c and returns a pointer pointing to the last matching character, or null if no match is found.

#include <stdio.h>

#include <string.h>

int main()

{

char str[50] = "Programming In C";

char *pos;

pos = strrchr(str, 'n');

if (pos)

printf("\n The last position of n is: %d", pos-str);

else

printf("\n n is not present in the string");

return 0;

}

Output

The last position of n is: 13

strcmp Function

int strcmp (const char *strl, const char *str2);

The strcmp function compares the string pointed to by str1 to the string pointed to by str2. The function returns zero if the strings are equal. Otherwise, it returns a value less than zero or greater than zero if str1 is less than or greater than str2 respectively.

#include <stdio.h>

#include <string.h>

int main()

{

char str1 [10] = "HELLO";

char str2 [10] = "HEY";

if (strcmp(str1, str2)==0)

printf("\n The two strings are identical");

else

printf("\n The two strings are not identical");

return 0;

}

Output

The two strings are not identical

strncmp Function

Syntax:

int strncmp (const char *strl, const char *str2, size_t n);

This function compares at most the first n bytes of strl and str2. The process stops comparing after the null character is encountered. The function returns zero if the first n bytes of the strings are equal. Otherwise, it returns a value less than zero or greater than zero if strl is less than or greater than str2, respectively.

#include <stdio.h>

#include <string.h>

int main()

{

char str1 [10] = "HELLO";

char str2 [10] = "HEY";

if (strncmp (strl, str2,2)==0)

printf("\n The two strings are identical");

else

printf("\n The two strings are not identical");

return 0;

}

Output

The two strings are identical

strcpy Function

Syntax:

char *strcpy (char *st rl, const char *str2);

This function copies the string pointed to by str2 str1 including the null character of str2. It returns the argument strl. Here str1 should be big enough to store the contents of str2.

#include <stdio.h>

#include <string.h>

int main()

{

char str1 [10], str2 [10] = "HELLO";

strcpy(strl, str2);

printf("\n strl: %s", strl);

return 0;

}

Output

HELLO

strncpy Function

Syntax:

char *strncpy (char *str1, const char *str2, size t n);

Programming Tip: Do not use string functions on a character array that is not terminated with a null character.

This function copies up to n characters from the string to str1. pointed to by str2 to str1 Copying stops when n characters are copied. However, if the null character in str2 is reached then the null character is continually copied to str1 until n characters have been copied. Finally, a null character must be appended to str1. However, if n is zero or negative then nothing is copied.

#include <stdio.h>

#include <string.h>

int main()

{

char str1 [10], str2 [10] = "HELLO";

strncpy (strl, str2, 2);

printf("\n str1: %s", str1);

return 0;

}

Output

HE

Note

To copy the string str2 in str1, a better way is to write

strncpy(strl, str2, sizeof(strl) −1);

This would enforce the copying of only that much characters for which str1 has space to accommodate. We have written size of str1 minus 1 to store the null character.

strlen Function

Syntax:

Size_t strlen (const char *str);

This function calculates the length of the string str up to but not including the null character, i.e., the function returns the number of characters in the string.

#include <stdio.h>

#include <string.h>

int main()

{

char str[] = "HELLO";

printf("\n Length of str is: %d", strlen(str));

return 0;

}

Output

Length of str is: 5

strstr Function

Syntax:

char *strstr(const char *strl, const char *str2);

This function is used to find the first occurrence of string str2 (not including the terminating null character) in the string str1. It returns a pointer to the first occurrence of str2 in strl. If no match is found, then a null pointer is returned.

#include <stdio.h>

#include <string.h>

int main()

{

char strl [] = "HAPPY BIRTHDAY TO YOU";

char str2 [] = "DAY";

char *ptr;

ptr = strstr(str1, str2);

if (ptr)

printf("\n Substring Found");

else

printf("\n Substring Not Found");

return 0;

}

Output

Substring Found

strspn Function

Syntax:

size_t strspn (const char *str1, const char *str2);

The function returns the index of the first character in str1 that doesn't match any character in str2.

#include <stdio.h>

#include <string.h>

int main()

{

char str1 [] = "HAPPY BIRTHDAY TO YOU";

char str2 [] = "HAPPY BIRTHDAY JOE";

printf("\n The position of first character in str2 that does not match with that in str1 is %d", strspn (strl, str2));

return 0;

}

Output

The position of first character in str2 that does not match with that in str1 is 15

strcspn Function

Syntax:

size_t strcspn (const char *strl, const char *str2);

The function returns the index of the first character in strl that matches any of the characters in str2.

#include <stdio.h>

#include <string.h>

int main()

{

char str1 [] = "PROGRAMMING IN C";

char str2 [] = "IN";

printf("\n The position of first character in str2 that matches with that in str1 is %d", strcspn (strl, str2));

return 0;

}

Output

The position of first character in str2 that matches with that in str1 is 8

strpbrk Function

Syntax:

char *strpbrk (const char *str1, const char *str2);

The function strpbrk () returns a pointer to the first occurrence in str1 of any character in str2, or NULL if none are present. The only difference between strpbrk() and strcspn is that strcspn () returns the index of the character and strpbrk () returns a pointer to the first occurrence of a character in str2.

#include <stdio.h>

#include <string.h>

int main( )

{

char str1 [] = "PROGRAMMING IN C";

char str2 [] = "AB";

char *ptr = strpbrk (strl, str2);

int main()

if (ptr = = NULL)

printf("\n No character matches in the two strings");

else

printf("\n Character in str2 matches with that in str1");

return 0;

}

Output

No character matches in the two strings

strtok Function

Syntax:

char *strtok ( char *strl, const char *delimiter );

The strtok () function is used to isolate sequential tokens in a null-terminated string, str. These tokens are separated in the string using delimiters. The first time that strtok is called, str should be specified; subsequent calls, wishing to obtain further tokens from the same string, should pass a NULL pointer instead. However, the delimiter must be supplied each time, though it may change between calls.

The strtok() function returns a pointer to the beginning of each subsequent token in the string, after replacing the token itself with a NULL character. When all tokens are left, a null pointer is returned.

#include <stdio.h>

#include <string.h>

main ()

{

char str[] = "Hello, to, the, world of, programming";

char delim [] ", ";

char result [20];

result = strtok (str, delim);

while (result!= NULL)

{

printf("\n %s", result);

result = strtok (NULL, delim);

}

getch();

return 0;

}

Output

Hello

to

the

world of

programming

strtol Function

Syntax:

long strtol (const char *str, char **end, int base);

The strtol function converts the string pointed by str to a long value. The function skips leading white space characters and stops when it encounters the first non- numeric character. strtol stores the address of the first invalid character in str in *end. If there were no digits at all, then the strtol function will store the original value of str in *end. You may pass NULL instead of *end if you do not want to store the invalid characters anywhere. Finally, the third argument base specifies whether the number is in hexa-decimal, octal, binary, or decimal representation.

#include <stdio.h>

#include <stdlib.h>

main ()

{

long num;

num = strtol ("12345 Decimal Value", NULL, 10);

printf("%ld", num);

num = strtol ("65432 Octal Value", NULL, 8);

printf("%ld", num);

strtol ("10110101 Binary Value", NULL, 2);

printf("%ld", num);

num = strtol ("A7CB4 Hexadecimal Value",NULL, 16);

printf("%ld", num);

getch();

return 0;

}

Output

12345

27418

181

687284

strtod Function

Syntax:

double strtod (const char *str, char **end);

The function accepts a string str that has an optional plus ('+') or minus sign (-) followed by either:

• a decimal number containing a sequence of decimal digits optionally consisting of a decimal point, or

• a hexadecimal number consisting of a "0x" or "0x" followed by a sequence of hexadecimal digits optionally containing a decimal point.

In both cases, the number may be optionally followed by an exponent ('E' or 'e' for decimal constants or a 'p' or 'p' for hexadecimal constants), followed by an optional plus or minus sign, followed by a sequence of decimal digits. For decimal constants and hexadecimal constants, the exponent indicates the power of 10 and 2, respectively, by which the number should be scaled.

#include <stdio.h>

#include <stdlib.h>

main ()

{

double num;

num = strtod ("123.345abcdefg", NULL);

printf("%lf", num);

getch();

return 0;

}

Output

123.345000

atoi () Function

Till now you must have understood that the value 1 is an integer and '1' is a character. So there is a huge difference when we write the two statements given below

int i=1; // here i =1

int i='1'; // here i =49, the ASCII value of character 1

Similarly, 123 is an integer number but '123' is a string of digits. What if you want to operate some integer operations on the string '123'? For this, C provides a function atoi that converts a given string into its corresponding integer.

The atoi() function converts a given string passed to it as an argument into an integer. The atoi() function returns that integer to the calling function. However, the string should start with a number. The atoi() will stop reading from the string as soon as it encounters a non-numerical character. The atoi() is included in the stdlib.h file. So before using this function in your program, you must include this header file. The syntax of atoi() can be given as,

int atoi( const char *str);

Example

i = atoi( "123.456" );

RESULT: i = 123

atof() Function

The function atof () converts the string that it accepts as an argument into a double value and then return that value to the calling function. However, the string must start with a valid number. One point to remember is that the string can be terminated with any non-numerical character, other than "E" or "e". The syntax of atof () can be given as,

 double atof ( const char *str);

Example

X = atof("12.39 is the answer" );

RESULT: x = 12.39

atol() Functions

The function atol () converts the string into a long int value. The atol function returns the converted long value to the calling function. Like atoi, the atol () will read from a string until it finds any character that should not be in a long. Its syntax can be given as,

long atol ( const char *str);

Example

X = atol ( "12345.6789" );

RESULT: x = 12345L.

Note

The functions atoi(), atof(), and atol() are a part of stdlib.h header file.