C++ cstring strncpy() Function

The C++ strncpy() function is a similar function as strcpy() function in C++, which is built-in and it is also a member of <cstring> header file. strncpy() is used to copy a string from one memory location to another memory location. This function is defined in the cstring header file.

Both are used for copying a string but the difference between them is that strncpy() function allows you to specify the number of characters to be copied from the source string to the destination string. This function takes three arguments, the destination string, the source string, and the number of characters to be copied.

Syntax

The syntax of the C++ strncpy() function −

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

Parameters

Following are the parameters of this function −

• destination: Pointer to the destination array where the content is to be copied.

• source: Pointer to the source of data to be copied.

• num: Number of characters to copy.

Return Value

The strncpy() function returns a pointer to the destination, which is the same as the destination pointer passed as the first argument.

Example 1

Let us understand how to use the C++ cstring strncpy() function with the help of an example.

In this example, let's try to copy the content of one string to another string using the strncpy() function. For this, we will create two strings, one source string and one destination string. We will then copy the content of the source string to the destination string using the strncpy() function.

#include <iostream>
#include <cstring>

using namespace std;

int main() {
    char source[] = "Hello, World!";
    char destination[100];

    // Copying the content of source string to destination string
    strncpy(destination, source, 5);
    destination[5] = '\0';

    cout << "Source: " << source << endl;
    cout << "Destination: " << destination << endl;

    return 0;
}

Output

When you run the program, the output will be:

Source: Hello, World!
Destination: Hello

Example 2

Let us understand another example of using the strncpy() function.

Here we will try to use strncpy() function to copy the content of other data types. Let's see what happens:

#include <iostream>
#include <cstring>

using namespace std;

int main(){
    int source = 12345;
    char destination[100];

    // Copying the content of source integer to destination string
    strncpy(destination, source, 5);
    destination[5] = '\0';

    cout << "Source: " << source << endl;
    cout << "Destination: " << destination << endl;

    return 0;
}

Output

When you run the program, the output will be:

The above code will not compile because the strncpy() function does not support copying the content of other data types.

error: invalid conversion from 'int' to 'const char*'