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strdup() and strndup() functions in C/C++

Last Updated : 23 Jul, 2025

The strdup() and strndup() functions are used to duplicate a string. 
strdup() : 
Syntax : char *strdup(const char *s); 
This function returns a pointer to a null-terminated byte string, which is a duplicate of the string pointed to by s. The memory obtained is done dynamically using malloc and hence it can be freed using free(). 
It returns a pointer to the duplicated string s.
Below is the C implementation to show the use of strdup() function in C:
 

// C program to demonstrate strdup()
#include<stdio.h>
#include<string.h>

int main()
{
    char source[] = "GeeksForGeeks";

    // A copy of source is created dynamically
    // and pointer to copy is returned.
    char* target = strdup(source); 

    printf("%s", target);
    return 0;
}

Output: 

GeeksForGeeks

strndup() : 
syntax: char *strndup(const char *s, size_t n); 
This function is similar to strdup(), but copies at most n bytes. 
Note: If s is longer than n, then only n bytes are copied, and a NULL ('\0') is added at the end.
Below is the C implementation to show the use of strndup() function in C:
 

// C program to demonstrate strndup()
#include<stdio.h>
#include<string.h>

int main()
{
    char source[] = "GeeksForGeeks";

    // 5 bytes of source are copied to a new memory
    // allocated dynamically and pointer to copied
    // memory is returned.
    char* target = strndup(source, 5);

    printf("%s", target);
    return 0;
}

Output:

Geeks

Let us see the differences in a tabular form -:

These functions are useful for duplicating strings in C++. The C++ Course provides insights into how to use strdup() and strndup() effectively, enhancing your string manipulation skills.

Its syntax is -:

char *strndup( const char *str, size_t size );

It takes two parameters that are -:
1.pointer to the null-terminated byte string to duplicate

2. max number of bytes to copy from str

Reference: Linux man(7)
 

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