In this Era of Programming, having knowledge of writing our own code for a given problem is must, but we should also be aware of the pre-defined functions that are provided to us in different libraries.
In Strings, several pre-defined functions are there in the <string.h> header file or library, which are useful in certain operations on strings. Some of the important and most used functions are listed below :
|
Function |
Use |
|
strlen() |
calculates the length of the string |
|
strcat() |
Appends one string at the end of another |
|
strncat() |
Appends first n-characters of a string at the end of another string |
|
strcpy() |
Copies a string into another |
|
strncpy() |
Copies first n-characters of one string into another |
|
strcmp() |
Compare two strings |
|
strncmp() |
Compare first n-characters of two strings |
|
strchr() |
Helps in finding the 1st occurrence of a given character in a string |
|
strrchr() |
Helps in finding the last occurrence of a given character in a string |
|
strstr() |
Finds the first occurrence of a given string in another string |
|
strrev() |
Finds the reverse of the string |
|
strtok() |
splits a string into token |
**********************
1. strlen() : This function is used to calculate the length of the string, it returns the length of the string as output . The returned value is of unsigned integer type. It doesn't counts the NULL character in the length.
#include <stdio.h>
#include <string.h>
int main()
{ int l1,l2;
char string1[50]="Coder";
char string2[50]={'c','o','d','e','r','\0'};
l1=strlen(string1);
l2=strlen(string2);
printf("Length of string1 is %d\n",l1);
printf("Length of string2 is %d\n",l2);
return 0;
}
OUTPUT
Length of string1 is 5
Length of string2 is 5
**********************
2. strcat() : This function is used to join (concatenate) 2 strings. It joins 1 string to the end of other. After joining, the new string formed is stored in the string whose name is written first in the function, and its size should also be much larger so as to accomodate the new string, otherwise an error can occur(Segmentation Fault).
#include <stdio.h>
#include <string.h>
int main() {
char str1[100] = "Hello";
char str2[10] = " World";
strcat(str1, str2);
puts(str1);
puts(str2);
return 0;
}
OUTPUT
Hello World
World
**********************
3. strncat() : This function helps in joining 2 strings but only for a specific number of characters. It is also called Bounded String Concatenation. It returns pointer of the destination string to whom the strings are joined.
#include <stdio.h>
#include <string.h>
int main ()
{
char str1[100] = "Hello";
char str2[10] = "World";
//After Concatenation
printf("String formed would be %s\n", strncat(str1, str2, 2));
// printing return value of strncat()
printf("Destination String is str1: %s", str1);
return 0;
}
OUTPUT
String after concatenation would be HelloWo
Destination String is str1: HelloWo
**********************
4. strcpy() : This fucntion copies the 1 string to another, i.e source to destination. If the size of the string we are copying the text is small, then un-defined behaviour can occur. Like Buffer Overflow.
#include <stdio.h>
#include <string.h>
int main()
{
char str1[100] = "Programmer Studios";
char str2[100];
strcpy(str2, str1);
puts(str2);
return 0;
}
OUTPUT
Programmer Studios
**********************
5. strncpy() : This function copies a string upto first n-characters.
#include <stdio.h>
#include <string.h>
int main()
{
char str1[20] = "Programmer Studios";
char str2[20];
strcpy(str2, str1,10);
puts(str2);
return 0;
}
OUTPUT
Programmer
**********************
6. strcmp() : This functions compares 2 strings and returns 0 is both are equal, or return a negative integer if the ASCII value of the 1st un-matched integer is smaller than the second, or returns a positive integer if the ASCII value of the 1st un-matched integer is greater than the second. It compares the strings character by character and continues until NULL character is not encountered.
#include <stdio.h>
#include <string.h>
int main()
{
char str1[10] = "abcd";
char str2[10] = "abed";
char str3[10] = "Lbem";
int r;
r = strcmp(str1, str2);
printf("strcmp(str1, str2) = %d\n", r);
r = strcmp(str1, str3);
printf("strcmp(str1, str3) = %d\n", r);
return 0;
}
OUTPUT
strcmp(str1, str2) = -1
strcmp(str1, str3) = 1
**********************
7. strncmp() : It compares first n-characters of the strings only. And then return the integer value correspondingly.
#include <stdio.h>
#include <string.h>
int main()
{
char str1[10] = "abcd";
char str2[10] = "abERkl";
int r;
r = strncmp(str1, str2, 4);
printf("strncmp(str1, str2,4) = %d\n", r);
return 0;
}
OUTPUT
strncmp(str1, str2) = 1
**********************
8. strchr() : This function searches for the 1st occurence of a character(suppose a), in the string. Then returns a pointer to the 1st occurence of that character, or NULL if it is not found.
#include <stdio.h>
#include <string.h>
int main ()
{
char str[] = "Programmer Studios";
char ch = 'm';
char *r;
r = strchr(str, ch);
printf("String is %s\n", r);
return(0);
}
OUTPUT
mmer Studios
**********************
9. strrchr() : This function searches for the last occurence of a character(suppose a), in the string. Then returns a pointer to the last occurence of that character, or NULL pointer if it is not found.
#include <stdio.h>
#include <string.h>
int main ()
{
char str[] = "Programmer Studios";
char ch = 'r';
char *r;
r = strrchr(str, ch);
printf("String is %s\n", r);
return(0);
}
OUTPUT
r Studios
**********************
10. strstr() : This function helps in finding the 1st occurence of a sub string in our string. It returns a pointer to the 1st occurence of the sub-string or returns null pointer if there is no sub string.
#include <stdio.h>
#include <string.h>
int main () {
char str[20] = "Programmer Studios";
char sub[10] = "Studios";
char *r;
r = strstr(str,sub);
printf("The substring is: %s\n", r);
return(0);
}
OUTPUT
Studios
**********************
11. strrev() : This function is used to reverse the given string.
#include<stdio.h>
#include<string.h>
int main()
{
char str[30] = "Coder";
printf("String before reversing is %s\n",str);
printf("String after reversing is %s",strrev(str));
return 0;
}
OUTPUT
redoC
**********************
12. strtok() : This function tokenizes/parses a given string using a delimiter. It returns a pointer to the 1st token found otherwise returns null pointer is token is not found in the whole string.
#include <string.h>
#include <stdio.h>
int main ()
{
char str[80] = "Coding,Programming,Writing";
char t[2] = ",";
char *token;
token = strtok(str, t);
while( token != NULL ) {
printf( " %s\n", token );
token = strtok(NULL, t);
}
return(0);
}
OUTPUT
Coding
Programming
Writing
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