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predefined string functions of C in string.h library

July 4, 2017 C C++ EXAMPLE FUNCTION 12834

This post contains a list of predefined string functions defined in string.h with examples. You can learn more about C string from our C course.

The functions present in the string.h header are:

Function Use
strlen calculates the length of string
strcat Appends one string at the end of another
strncat Appends first n characters of a string at the end of another
strcpy Copies a string into another
strncpy Copies first n characters of one string into another
strcmp Compares two strings
strncmp Compares first n characters of two strings
strchr Finds the first occurrence of a given character in a string
strrchr Finds the last occurrence of a given character in a string
strstr Finds the first occurrence of a given string in another string
strcspn Calculates the initial length of a string, not containing any character of the other string
strspn Calculates the initial length of a string, containing the only characters of the other string
strpbrk Finds the first occurrence of any of the characters of a string in another string
strtok splits a string into token

Examples


strlen

strlen(s1) calculates the length of string s1.

#include <stdio.h>
#include <string.h>
int main()
{
  char name[ ]= "Hello"; 
  int len1, len2;
  len1 = strlen(name); 
  len2 = strlen("Hello World");
  printf("length of %s = %d\n", name, len1); 
  printf("length of %s = %d\n", "Hello World", len2);
  return 0;
}

Output

length of Hello = 5 
length of Hello World = 11

strlen doesn't count '\0' while calculating the length of a string.

strcat

strcat(s1, s2) concatenates(joins) the second string s2 to the first string s1.

#include <stdio.h>
#include <string.h>
int main()
{
  char s2[ ]= "World"; 
  char s1[20]= "Hello"; 
  strcat(s1, s2);
  printf("Source string = %s\n", s2); 
  printf("Target string = %s\n", s1); 
  return 0;
}

Output

Source string = World 
Target string = HelloWorld

strncat

strncat(s1, s2, n) concatenates(joins) the first ‘n’ characters of the second string s2 to the first string s1.

#include <stdio.h>
#include <string.h>
int main()
{
  char s2[ ]= "World"; 
  char s1[20]= "Hello"; 
  strncat(s1, s2, 2);
  printf("Source string = %s\n", s2); 
  printf("Target string = %s\n", s1); 
  return 0;
}

Source string = World
Target string = HelloWo

strcpy

strcpy(s1, s2) copies the second string s2 to the first string s1.

#include <string.h>
#include <stdio.h>
int main()
{
  char s2[ ]= "Hello"; 
  char s1[10]; 
  strcpy(s1, s2);
  printf("Source string = %s\n", s2); 
  printf("Target string = %s\n", s1); 
  return 0;
}

Output

Source string = Hello
Target string = Hello

strncpy

strncpy(s1, s2, n) copies the first ‘n’ characters of the second string s2 to the first string s1.

#include <string.h>
#include <stdio.h>
int main()
{
  char s2[ ]= "Hello"; 
  char s1[10]; 
  strncpy(s1, s2, 2);
  s1[2] = '\0';   /* null character manually added */
  printf("Source string = %s\n", s2); 
  printf("Target string = %s\n", s1); 
  return 0;
}

Output

Source string = Hello
Target string = He

Please note that we have added the null character (‘\0’) manually.

strcmp

strcmp(s1, s2) compares two strings and finds out whether they are same or different. It compares the two strings character by character till there is a mismatch. If the two strings are identical, it returns a 0. If not, then it returns the difference between the ASCII values of the first non-matching pair of characters.

#include <stdio.h>
#include <string.h>
int main()
{
  char s1[ ]= "Hello"; 
  char s2[ ]= "World"; 
  int i, j;
  i = strcmp(s1, "Hello");
  j = strcmp(s1, s2);
  printf("%d \n %d\n", i, j);
  return 0;
}


-15

The difference between the ASCII values of H(72) and W(87) is -15.

strncmp

strncmp(s1, s2, n) compares the first ‘n’ characters of s1 and s2.

#include <stdio.h>
#include <string.h>
int main()
{
  char s1[ ]= "Hello"; 
  char s2[ ]= "World"; 
  int i, j;
  i = strncmp(s1, "He BlogsDope", 2);
  printf("%d\n", i);
  return 0;
}

Output

0

strchr

strchr(s1, c) returns a pointer to the first occurrence of the character c in the string s1 and returns NULL if the character c is not found in the string s1.

#include <stdio.h>
#include <string.h>
int main()
{
  char s1[ ]= "Hello Blogsdope"; 
  char c = 'B';
  char *p;
  p = strchr(s1, c);
  printf("%s\n", p);
  return 0;
}

Output

Blogsdope

strrchr

strrchr(s1, c) returns a pointer to the last occurrence of the character c in the string s1 and returns NULL if the character c is not found in the string s1.

#include <stdio.h>
#include <string.h>
int main()
{
  char s1[ ]= "Hello Blogsdope"; 
  char c = 'o';
  char *p;
  p = strrchr(s1, c);
  printf("%s\n", p);
  return 0;
}

Output

ope

strstr

strstr(s1, s2) finds the first occurrence of the string s2 in the string s1.

#include <stdio.h>
#include <string.h>
int main()
{
  char s1[ ]= "HelloBlogsdope"; 
  char s2[ ] = "Blog";
  char *p;
  p = strstr(s1, s2);
  printf("%s\n", p);
  return 0;
}

Output

BlogsDope

strcspn

strcspn(s1, s2) returns the length of the initial part of the string s1 not containing any of the characters of the string s2.

#include <stdio.h>
#include <string.h>
int main()
{
  char s1[ ]= "HelloBlogsdope"; 
  char s2[ ] = "lo";
  int i = strcspn(s1, s2);
  printf("The first character is matched at %d\n", i+1);
  return 0;
}

Output

The first character is matched at 3

strspn

strspn(s1, s2) returns the length of the initial part of the string s1 only containing the characters of the string s2.

#include <stdio.h>
#include <string.h>
int main()
{
  char s1[ ]= "123abc"; 
  char s2[ ] = "123456790";
  int i = strspn(s1, s2);
  printf("%d\n", i);
  return 0;
}

Output

3

strpbrk

strpbrk(s1, s2) returns the first occurrence of any of the characters of the string s2 in the string s1.

#include <stdio.h>
#include <string.h>
int main()
{
  char s1[ ]= "Hey 123 Blogsdope"; 
  char s2[ ] = "123456790";
  char *p;
  p = strpbrk(s1, s2);
  printf("%s\n", p);
  return 0;
}

Output

123 Blogsdope

strtok

strtok(s1, s2) finds s2 in s1 and returns a pointer to it and returns NULL if not found.

#include <stdio.h>
#include <string.h>
int main()
{
  char s1[ ]= "Hey,123,Blogsdope";
  char *p;
  p = strtok(s1, ",");

  while(p != NULL)
  {
	printf("%s\n", p);
	p = strtok(NULL, ",");
  }
  return 0;
}

Output

Hey
123
Blogsdope


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