Updates:

• 2020-04-30 – Added missing semicolon in code and updated example.

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NOTE: This article was originally written a few years ago, so some references may be out of date.

I have been enjoying working on the SirSound project the past month, as well as some fun challenges at my day job. Every now and then I run into something I’d like to do that is not doable in C, or doable but not proper to do in C, or … maybe doable. It’s sometimes difficult for me to find answers when I do not know how to ask the question.

With that said, I have a C question for anyone who might be able to answer it.

Using my multi-track music sequencer as an example, consider representing data like this:

[sequence]
  [track]
    [note /]
    [note /]
    [note /]
  [/track]
  [track]
    [note /]
    [note /]
    [note /]
  [/track]
[/sequence]

It’s easy to create a sequence like this in C. Here’s some pseudo code:

track1 = { C, C, C, C };
track2 = { E, E, E, E };
sequence1 = { track1, track 2};

I thought there might be a clever way to do all of this with one initializer.  If I treat the data like nested XML (like the first example), I thought it might be possible to do something like this:

typedef struct SentenceStruct SentenceStruct;

struct SentenceStruct
{
  char           *Word;
  SentenceStruct *Next;
};

Something like this allows me to represent that tree of data very easily, and I find many examples of building things like this in C code:

int main()
{
   SentenceStruct Word1;
   SentenceStruct Word2;
   SentenceStruct Word3;

   Word1.Word = "sequence";
   Word1.Next = &Word2;

   Word2.Word = "track";
   Word2.Next = &Word3;

   Word3.Word = "note1";
   Word3.Next = NULL;

   SentenceStruct *Word;

   Word = &Word1;

   while( Word != NULL )
   {
      printf("%s ", Word->Word);
      if (Word->Next == NULL) break;
      Word = Word->Next;
   }
   printf("\n");

   return EXIT_SUCCESS;
}

This creates a single linked list of words, then prints them out.

I thought it might be possible to initialize the whole thing, like this:

 SentenceStruct sentence =
 {
   { "kitchen", { "light", { "ceiling", { "on", NULL }}}};
 }

…though the address of “light” is quite different than the address of a structure which contains a pointer that should point to “light”.

I was going to make each one a pointer to an array of words, so I could have a tree of words like the earlier example (with kitchen/light and kitchen/fan):

typedef struct SentenceStruct SentenceStruct;

struct SentenceStruct
{
  char *Word;
  SentenceStruct *Next[];
}

Does anyone know how (or if) this can be done in C?

Thoughts?