strdup() in C and Portable String Duplication

strdup() allocates memory for a copy of a null-terminated string and returns a pointer to the new copy. It was widely available through POSIX before being added to the C standard in C23.

strdup() Syntax Top ↑

char *copy = strdup(source);  // C23; historically POSIX

The returned allocation must be released with free() when it is no longer needed.

Portable Duplicate Function for C11/C17 Top ↑

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

char *duplicate_string(const char *source) {
    size_t length = strlen(source) + 1;
    char *copy = malloc(length);

    if (copy != NULL) {
        memcpy(copy, source, length);
    }

    return copy;
}

int main(void) {
    const char *original = "plus2net";
    char *copy = duplicate_string(original);

    if (copy == NULL) {
        printf("Memory allocation failed.\n");
        return 1;
    }

    printf("Original: %s\n", original);
    printf("Copy: %s\n", copy);

    free(copy);
    return 0;
}

Duplicate an Array of Names Top ↑

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

char *duplicate_string(const char *source) {
    size_t length = strlen(source) + 1;
    char *copy = malloc(length);

    if (copy != NULL) {
        memcpy(copy, source, length);
    }

    return copy;
}

int main(void) {
    const char *names[] = {"Alice", "Bob", "Charlie"};
    char *copies[3] = {NULL, NULL, NULL};

    for (size_t i = 0; i < 3; i++) {
        copies[i] = duplicate_string(names[i]);

        if (copies[i] == NULL) {
            printf("Allocation failed.\n");

            for (size_t j = 0; j < i; j++) {
                free(copies[j]);
            }

            return 1;
        }
    }

    for (size_t i = 0; i < 3; i++) {
        printf("%s\n", copies[i]);
        free(copies[i]);
    }

    return 0;
}

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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