C – strncpy() function

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  • strncpy( ) function copies portion of contents of one string into another string. Syntax for strncpy( ) function is given below.

char * strncpy ( char * destination, const char * source, size_t num );

  • Example:

strncpy ( str1, str2, 4) – It copies first 4 characters of str2 into str1.
strncpy ( str2, str1, 4) – It copies first 4 characters of str1 into str2.

……

  • If destination string length is less than source string, entire source string value won’t be copied into destination string.
  • For example, consider destination string length is 20 and source string length is 30.
  • If you want to copy 25 characters from source string using strncpy( ) function, only 20 characters from source string will be copied into destination string and remaining 5 characters won’t be copied and will be truncated.

Example program for strncpy( ) function in C:

    • In this program, only 5 characters from source string “cprogramming” is copied into target string using strncpy( ) function.
#include <stdio.h>
#include <string.h>

int main( )
{
   char source[ ] = "cprogramming" ;
   char target[20]= "" ;
   printf ( "nsource string = %s", source ) ;
   printf ( "ntarget string = %s", target ) ;
   strncpy ( target, source, 5 ) ;
   printf ( "ntarget string after strcpy( ) = %s", target ) ;
   return 0;
}

Output:

source string = cprogramming
target string =
target string after strncpy( ) = fresh

Other C String functions:

    • String.h header file supports all the string functions in C language. All the string functions are given below.
    • Click on each string function name below to display example programs.
S.no
String functions
Description
1 strcat ( )  Concatenates str2 at the end of str1.
2 strncat ( )  appends a portion of string to another
3 strcpy ( )  Copies str2 into str1
4 strncpy.(.)  copies given number of characters of one string to another
5 strlen ( )  gives the length of str1.
6 strcmp ( )  Returns 0 if str1 is same as str2. Returns <0 if strl < str2. Returns >0 if str1 > str2.
7 strcmpi ( )  Same as strcmp() function. But, this function negotiates case.  “A” and “a” are treated as same.
8 strchr ( )  Returns pointer to first occurrence of char in str1.
9 strrchr ( )  last occurrence of given character in a string is found
10 strstr ( )  Returns pointer to first occurrence of str2 in str1.
11 strrstr ( )  Returns pointer to last occurrence of str2 in str1.
12 strdup ( )  duplicates the string
13 strlwr ( )  converts string to lowercase
14 strupr ( )  converts string to uppercase
15 strrev ( )  reverses the given string
16 strset ( )  sets all character in a string to given character
17 strnset ( )  It sets the portion of characters in a string to given character
18 strtok ( )  tokenizing given string using delimiter

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