strncat() in C: Append Part of a String

strncat() appends at most n characters from the source string and then adds a terminating null character. The destination still needs enough capacity for its existing text, the appended characters and \0.

Syntax Top ↑

strncat(destination, source, n);

Append Five Characters Top ↑

#include <stdio.h>
#include <string.h>

int main(void) {
    char destination[30] = "welcome to ";
    char source[] = "plus2net";

    strncat(destination, source, 5);
    printf("%s\n", destination);
    return 0;
}

Output

welcome to plus2

Check Available Capacity Top ↑

#include <stdio.h>
#include <string.h>

int main(void) {
    char destination[20] = "Plus2Net ";
    char source[] = "C Tutorial";
    size_t count = 5;
    size_t available = sizeof(destination) - strlen(destination) - 1;

    if (count > available) {
        count = available;
    }

    strncat(destination, source, count);
    printf("%s\n", destination);
    return 0;
}

How strncat() Works Top ↑

#include <stdio.h>
#include <string.h>

char *custom_strncat(char *destination, const char *source, size_t n) {
    char *end = destination + strlen(destination);

    while (*source != '\0' && n > 0) {
        *end++ = *source++;
        n--;
    }

    *end = '\0';
    return destination;
}

int main(void) {
    char destination[20] = "Hello, ";

    custom_strncat(destination, "World!", 3);
    printf("%s\n", destination);
    return 0;
}

Output

Hello, Wor

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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