Cool Dynamic String Implementation in C inspired by Redis SDS

cool_dynamic_string.c

#include "stdio.h"
#include "string.h"
#include "stdlib.h"


// HEADER_SIZE would help us to move pointer to and fro
// usually, sizeof(unsigned int) is 4 bytes
// so this will be 8 bytes
#define HEADER_SIZE 2 * sizeof(unsigned int)


struct DynamicStr
{
    unsigned int len;
    unsigned int capacity;
    char data[];
};

typedef struct DynamicStr DStr; // To make our lives easier

const DStr* get_dstr(const char *d);

char *newString(const char *data)
{
    DStr *new_str;

    int len = strlen(data);

    int struct_size = HEADER_SIZE + len + 1; // Reserving memory of length, 

    new_str = (DStr *)malloc(struct_size); // Allocate memory for struct
    new_str->len = len;
    new_str->capacity = len;

    memcpy(new_str->data, data, len); // Copy source string content to new string

    new_str->data[len + 1] = '\0'; // Adding a null terminator

    return new_str->data;
}

unsigned int len(const char *d)
{
    return get_dstr(d)->len;
}


const DStr* get_dstr(const char *d)
{
    DStr *dstr = (DStr *)(d - HEADER_SIZE);  // This moves str pointer HEADER_SIZE slots back
                                            // so that we can get the starting position of DStr
    return dstr;
}

int main()
{

    char *new_str = newString("Hello World");
    printf("Dynamic String: %s", new_str);
    printf("Dynamic String Length: %u", len(new_str));
    return 0;
}