Strings and string manipulations

String is nothing but an array of characters (OR char data types). While doing programming in C language, you may have faced challenges wherein you might want to compare two strings, concatenate strings, copy one string to another & perform various string manipulation operations. All of such kind of operations plus many more other functions are available in “string.h” header file. In order to use these string functions you must include string.h file in your C program.

In simple words, String is an one dimensional array of characters.

String Declaration

Method 1:

char address[]={'T', 'E', 'X', 'A', 'S', '\0'};

Method 2: The above string can also be defined as –

char address[]="TEXAS";

In the above declaration NULL character (\0) will automatically be inserted at the end of the string.

What is NULL Char “\0”?
'\0' represents the end of the string. It is also referred as String terminator & Null Character.

String I/O

Read & Write Strings Using Printf and Scanf –

#include <stdio.h>
#include <string.h>
int main()
{
    /* String Declaration*/
    char nickname[20];

    printf("Enter your Nick name:");

    /*I am reading the input string and storing it in nickname*/
    scanf("%s", &nickname);

    /*Displaying String*/
    printf("%s",nickname);

    return 0;
}

Note: %s is used for strings I/O

Read & Write Strings Using gets and puts –

#include <stdio.h>
#include <string.h>
int main()
{
    /* String Declaration*/
    char nickname[20];

    /* Console display using puts */
    puts("Enter your Nick name:");

    /*Input using gets*/
    gets(nickname);

    puts(nickname);

    return 0;
}

String functions

strlen function: size_t strlen(const char *str)

size_t represents unsigned short
It returns the length of the string without including end character (terminating char ‘\0’).

Example:

#include <stdio.h>
#include <string.h>
int main()
{
     char str1[20] = "BeginnersBook";
     printf("Length of string str1: %d", strlen(str1));
     return 0;
}

Output:

Length of string str1: 13

strlen vs sizeof
strlen returns you the length of the string stored in array, however sizeof returns the total allocated size assigned to the array. So if I consider the above example again then the following statements would return the below values.

strlen(str1) returned value 13.
sizeof(str1) would return value 20 as the array size is 20 (see the first statement in main function).

strnlen function: size_t strnlen(const char *str, size_t maxlen)

size_t represents unsigned short
It returns length of the string if it is less than the value specified for maxlen (maximum length) otherwise it returns maxlen value.

Example:

#include <stdio.h>
#include <string.h>
int main()
{
     char str1[20] = "BeginnersBook";
     printf("Length of string str1 when maxlen is 30: %d", strnlen(str1, 30));
     printf("Length of string str1 when maxlen is 10: %d", strnlen(str1, 10));
     return 0;
}

Output:
Length of string str1 when maxlen is 30: 13
Length of string str1 when maxlen is 10: 10

Have you noticed the output of second printf statement, even though the string length was 13 it returned only 10 because the maxlen was 10.

strcmp function: int strcmp(const char *str1, const char *str2)

It compares the two strings and returns an integer value. If both the strings are same (equal) then this function would return 0 otherwise it may return a negative or positive value based on the comparison.

If string1 < string2 OR string1 is a substring of string2 then it would result in a negative value. If string1 > string2 then it would return positive value.
If string1 == string2 then you would get 0(zero) when you use this function for compare strings.

Example:

#include <stdio.h>
#include <string.h>
int main()
{
     char s1[20] = "BeginnersBook";
     char s2[20] = "BeginnersBook.COM";
     if (strcmp(s1, s2) ==0)
     {
        printf("string 1 and string 2 are equal");
     }else
      {
         printf("string 1 and 2 are different");
      }
     return 0;
}

Output:

string 1 and 2 are different

strncmp function: int strncmp(const char *str1, const char *str2, size_t n)

size_t is for unassigned short
It compares both the string till n characters or in other words it compares first n characters of both the strings.

Example:

#include <stdio.h>
#include <string.h>
int main()
{
     char s1[20] = "BeginnersBook";
     char s2[20] = "BeginnersBook.COM";
     /* below it is comparing first 8 characters of s1 and s2*/
     if (strncmp(s1, s2, 8) ==0)
     {
         printf("string 1 and string 2 are equal");
     }else
     {
         printf("string 1 and 2 are different");
     }
     return 0;
}

Output:

string1 and string 2 are equal

strcat function: char *strcat(char *str1, char *str2)

It concatenates two strings and returns the combined one string.

Example:

#include <stdio.h>
#include <string.h>
int main()
{
     char s1[10] = "Hello";
     char s2[10] = "World";
     strcat(s1,s2);
     printf("Output string after concatenation: %s", s1);
     return 0;
}

Output:

Output string after concatenation: HelloWorld

strncat function: char *strncat(char *str1, char *str2, int n)

It concatenates n characters of str2 to string str1. A terminator char (‘\0’) will always be appended at the end of the concatenated string.

Example:

#include <stdio.h>
#include <string.h>
int main()
{
     char s1[10] = "Hello";
     char s2[10] = "World";
     strncat(s1,s2, 3);
     printf("Concatenation using strncat: %s", s1);
     return 0;
}

Output:

Concatenation using strncat: HelloWor

strcpy function: char *strcpy( char *str1, char *str2)

It copies the string str2 into string str1, including the end character (terminator char ‘\0’).

Example:

#include <stdio.h>
#include <string.h>
int main()
{
     char s1[30] = "string 1";
     char s2[30] = "string 2 : I’m gonna copied into s1";
     /* this function has copied s2 into s1*/
     strcpy(s1,s2);
     printf("String s1 is: %s", s1);
     return 0;
}

Output:

String s1 is: string 2: I’m gonna copied into s1

char *strncpy( char *str1, char *str2, size_t n)

size_t is unassigned short and n is a number.
Case1: If length of str2 > n then it just copies first n characters of str2 into str1.
Case2: If length of str2 < n then it copies all the characters of str2 into str1 and appends several terminator chars(‘\0’) to accumulate the length of str1 to make it n.

Example:

#include <stdio.h>
#include <string.h>
int main()
{
     char first[30] = "string 1";
     char second[30] = "string 2: I’m using strncpy now";
     /* this function has copied first 10 chars of s2 into s1*/
     strncpy(s1,s2, 12);
     printf("String s1 is: %s", s1);
     return 0;
}

Output:

String s1 is: string 2: I’m

strchr function: char *strchr(char *str, int ch)

It searches string str for character ch (you may be wondering that in above definition I have given data type of ch as int, don’t worry I didn’t make any mistake it should be int only. The thing is when we give any character while using strchr then it internally gets converted into integer for better searching.

Example:

#include <stdio.h>
#include <string.h>
int main()
{
     char mystr[30] = "I’m an example of function strchr";
     printf ("%s", strchr(mystr, 'f'));
     return 0;
}

Output:

f function strchr

Strrchr function: char *strrchr(char *str, int ch)

It is similar to the function strchr, the only difference is that it searches the string in reverse order, now you would have understood why we have extra r in strrchr, yes you guessed it rite it is for reverse only.

Now let’s take the same above example:

#include <stdio.h>
#include <string.h>
int main()
{
     char mystr[30] = "I’m an example of function strchr";
     printf ("%s", strrchr(mystr, 'f'));
     return 0;
}

Output:

function strchr

Why output is different than strchr? It is because it started searching from the end of the string and found the first ‘f’ in function instead of ‘of’.

strstr function: char *strstr(char *str, char *srch_term)

It is similar to strchr, except that it searches for string srch_term instead of a single char.

Example:

#include <stdio.h>
#include <string.h>
int main()
{
     char inputstr[70] = "String Function in C at BeginnersBook.COM";
     printf ("Output string is: %s", strstr(inputstr, 'Begi'));
     return 0;
}

Output:

Output string is: BeginnersBook.COM

You can also use this function n place of strchr as you are allowed to give single char also in place of search_term string.