ft_strdup — Duplicate a String

Allowed functions: malloc

Reproduce the behavior of the function strdup (man strdup).

char    *ft_strdup(char *src);

Solution

Download ft_strdup.c

#include <stdlib.h>

char *ft_strdup(char *src) {
	int i = 0;

	while (src[i])
		i++;

	char *dup = malloc(sizeof(char) * (i + 1));
	if (!dup)
		return (NULL);

	i = 0;
	while (src[i]) {
		dup[i] = src[i];
		i++;
	}
	dup[i] = '\0';
	return dup;
}

How It Works

Goal: Create a heap-allocated copy of a string.

Approach: Measure the string length, allocate memory with malloc, then copy every character manually.

Step by step:

1. Count the length of src by iterating until the null terminator.
2. Allocate length + 1 bytes with malloc (the extra byte is for the null terminator).
3. If malloc fails, return NULL.
4. Copy each character from src to dup in a loop, then null-terminate dup.

Key concept: Dynamic memory allocation with malloc and the responsibility to allocate the right size (including the null terminator).