C – strncat() function

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strncat() function in C:

  • strncat( ) function in C language concatenates (appends) portion of one string at the end of another string. Syntax for strncat( ) function is given below.
    char * strncat ( char * destination, const char * source, size_t num );
  • Example :
    strncat ( str2, str1, 3 ); – First 3 characters of str1 is concatenated at the end of str2.
    strncat ( str1, str2, 3 ); – First 3 characters of str2 is concatenated at the end of str1.
  • As you know, each string in C is ended up with null character (‘\0’).
  • In strncat( ) operation, null character of destination string is overwritten by source string’s first character and null character is added at the end of new destination string which is created after strncat( ) operation.

Example program for strncat( ) function in C:

In this program, first 5 characters of the string “fresh2refresh” is concatenated at the end of the string “C tutorial” using strncat( ) function and result is displayed as “C tutorial fres”.


Source string                       = fresh2refresh
Target string                        = C tutorial
Target string after strcat( ) = C tutorial fres

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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