Question

I have 2 questions.

I want to create an array of files in C. But I’m not sure whether I have to malloc the size before or not.Can I just use FILE** files as an array or do I have to malloc them before. And if I have to make space, do I need to reserve 4 bytes (x86)?

I have the variable “char extra[8] = { 0xAE00AF00B000B100 };” and I want to assign it to the end of another char array[24]. Is there a faster way of doing that without having to type in every value by hand or using a for loop.

char extra[8] = { 0xAE00AF00B000B100 };
// index is a random place in the string
name[index] = '\0';
i = 0;
if (index > 16) {
    for (i = 24-index; i < 8; i++) {
        index++;
        name[index] = extra[i];
        }
    }
else {
    name[17] = 0xAE;
    name[18] = 0x00;
    name[19] = 0xAF;
    name[20] = 0x00;
    name[21] = 0xB0;
    name[22] = 0x00;
    name[23] = 0xB1;
    name[24] = 0x00;
}

I need to add those extra bytes btw.

Answer 1

I want to create an array of files in C. But I’m not sure whether I
have to malloc the size before or not.Can I just use FILE** files as
an array or do I have to malloc them before. And if I have to make
space, do I need to reserve 4 bytes (x86)?

If you need to have an array of files, it is possible to use an array of pointers as follow:

#include <stdio.h>

FILE *array[NB_FILES];

Or you can do it dynamically if NB_FILES is only known at runtime.

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

FILE **array = malloc(nb_files * sizeof *array);

I have the variable “char extra[8] = { 0xAE00AF00B000B100 };” and I want to assign it to the end of another char array[24]. Is there a faster way of doing that without having to type in every value by hand or using a for loop.

The standard C library provides the function memcpy, which is a builtin on many compiler (so it will be faster than a for loop).

#include <string.h>

char array[24];
char extra[8];

memcpy(array + sizeof array - sizeof extra - 1, extra, sizeof extra);