C – strncpy() function

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strncpy() function in C:

  • 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 “fresh2refresh” is copied into target string using strncpy( ) function.


source string = fresh2refresh
target string =
target string after strncpy( ) = fresh

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 for detail description and example programs.
String functions
strcat ( ) Concatenates str2 at the end of str1
strncat ( ) Appends a portion of string to another
strcpy ( ) Copies str2 into str1
strncpy ( ) Copies given number of characters of one string to another
strlen ( ) Gives the length of str1
strcmp ( ) Returns 0 if str1 is same as str2. Returns <0 if strl < str2. Returns >0 if str1 > str2
strcmpi ( ) Same as strcmp() function. But, this function negotiates case.  “A” and “a” are treated as same.
strchr ( ) Returns pointer to first occurrence of char in str1
strrchr ( ) last occurrence of given character in a string is found
strstr ( ) Returns pointer to first occurrence of str2 in str1
strrstr ( ) Returns pointer to last occurrence of str2 in str1
strdup ( ) Duplicates the string
strlwr ( ) Converts string to lowercase
strupr ( ) Converts string to uppercase
strrev ( ) Reverses the given string
strset ( ) Sets all character in a string to given character
strnset ( ) It sets the portion of characters in a string to given character
strtok ( ) Tokenizing given string using delimiter

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