variable array size at arduino

Question

I have an SD card which I filled with 15 mp3 tracks and a text file that has 15 words and 15 tracks names. My question is regarding initializing the following

char* words[ ]
char* tracks [ ]

When I initialize them as [100] and [100], the listing of the dB doesn't work as I currently only have 15 tracks and words. I want code to have the ability to place 999.

So my question is: can I make both them variable arrays and how?

I tried leaving between the brackets empty and several other methods but they didn't work. So I wondering if anyone here have any other suggestions.

Use dynamic memory allocations, malloc and then realloc? — Alok Save
– Alok Save, Commented Dec 29, 2013 at 15:44
I tried using malloc but it didn't work, however will try to use realloc, thanks for your fast reply :D — user3133400
– user3133400, Commented Dec 29, 2013 at 15:50
Note char*words[] is an array of pointers! You will need buffer for string data also char[][]. As this is all dynamic, you better not use static arrays, but use some new keywords. — LS_ᴅᴇᴠ
– LS_ᴅᴇᴠ, Commented Dec 30, 2013 at 10:31

AlkH · Accepted Answer · 2016-02-11 07:30:45Z

1

Arduino version of C/C++ has a great feature - VLA (variable length array, from C99) So, just use:

void process(int n)
{
    // Set up a buffer of n characters
    char b[n];
    // do the work
}

See: http://www.drdobbs.com/the-new-cwhy-variable-length-arrays/184401444

You need array of arrays? No problem (I hope). Pseudocode:

char* words[N]; // N - words
char word1[M] // M - word length
char word2[O] // O - second word length

words[0] = word1;
words[1] = word2;

Many answers suggest to use dynamic memory allocation - it works, but main drawback of such method - memory fragmentation. But remember - dynamic memory allocation is only method to return arrays from functions!

P.S. I can't verify code with compiler at the moment - please give me feedback if it doesn't work.

edited Feb 11, 2016 at 7:30

answered Feb 11, 2016 at 7:14

AlkH

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Titou · Accepted Answer · 2013-12-29 15:58:34Z

0

Arduino code is compiled as C++; you can use the new char[size] and delete[] operators.

answered Dec 29, 2013 at 15:58

Titou

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1 Comment

user3133400 Over a year ago

I tried what still i didnt get anything but when i tried using: //words = (char** )calloc(track_size++,sizeof(char*)); //tracks = (char** )calloc(track_size++,sizeof(char*)); with delete []; it only outputs the last word and last track, i dont understand why??

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