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  • Author Author: phoenixcomm
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Flight Simulator 101 or back to college - part 16: C Structures with in Structures

phoenixcomm

imageNow, Somewhere on the Stack Exchange, I heard some crud about you just can't have a struct as a member of a struct. Well, you sure can and now for all the curious minds out there I will show you how to do it. Remember I work with flight simulation, so you always need to know where you are. This is called position, and it is made up of both a Latitude and a Longitude which are both structures of themselves, enclosed in an outer structure. 

First I need to create two structs called Lat and Lon and I will make them out of a structure that I call DM, or Degrees and Minutes, and you also need to know the Hemisphere or hemi. 

struct DM {
	int degrees;
	float minutes;
	char hemi; 
	};

struct DM Lat;
struct DM Lon;
Now that I have that out of the way, I need to put this                   together and create my three structures: Current, Start, and Finish. You will note they all have a             structure type of Position. So you ask how do I access them? Well, you just use dotted notation.

struct Position{
	struct DM Lat;
	struct DM Lon; } Current, Start, Finish;
// Carswell: 32-46.151167N 097-26.492083W
	Start.Lon.degrees  = 32;
	Start.Lon.minutes  = 46.151167;
	Start.Lon.hemi     = 'N';
	Start.Lat.degrees  = 97;
	Start.Lat.minutes  = 26.492083;
	Start.Lat.hemi     = 'W';

Now, I hope I have helped some of you.. I think this will close this blog.  

  • in reply to Andrew J

    I must have had a typo when I first put a struct in a struct. I use GCC and It works fine. -enjoy

    struct test {
    struct member {
    float x;
    float y;
    int degress; } angle
    int itemNumber;
    char discription[50];
    float weight; }TEST;

    I might have tried to declare an array char[50] description -LOL
    In my simulator, my aircraft model consists of a STRUCT with more than a few more STRUCTs in it. ie.:

    where things are measured from the tip of the tail forward, right wing to left, and the top of the tail to the ground.
    struct XYZ {
    float X;
    float Y;
    float Z;} XYZpart, XYZac, XYZmate;

    struct Locations {
    struct XYZpart;
    struct XYZac;
    struct XYZmate;}
    float partWeight;
    char partName[50];
    char partNumber[50];
    char atachName[50];
    char atachNumber[50];}Parts;
  • in reply to colporteur

    Nesting of structures is covered pretty well in the short Microchip course:
    https://mu.microchip.com/advanced-c-programming

    Data Structures

    • Structures (14 min)
    • Unions (8 min)

    Lab1 - Nested Structures and Pointers to Unions and Structures (17 min)

    • In this section you will learn:
      • How to nest structures and unions
      • How to create pointers to unions and structures
      • How to use structure and union pointers

    One good thing about the lab is that it shows you how the data structure appears in memory:  

    image

    so in this case you can see the members of a union sharing the same address space, and the members of a nested struct using contiguous addresses.

    Sometimes the layers of abstraction can overly obfuscate an otherwise relatively simple concept. 

    But, as the saying goes, "you can lead a horse to water..."  Slight smile

  • K&R edition 2 [the 'ANSI C' one] says: "Structures can be nested."

    I don't understand why you need to create instances of the first structure before incorporating it within the second.

    What are you using for a compiler? I've just tried the following simple program with VC++ 2010 and it compiled and ran fine.

    image

  • in reply to phoenixcomm

    Interestingly, Smalltalk has no basic types, pretty much everything is an Object and thus has a Class definition (even Class is an instance of Metaclass, one of the few things that aren’t objects.  Most non-Smalltalk devs would declare it the Devil’s work because “not type safe” but that really wasn’t (isn’t) a problem.  I would hazard a guess that very little is developed in at language now but it was a really good language to use for OO development and when I transitioned to Java I used to curse it for having to deal with basic non-object types!

  • in reply to phoenixcomm

    Ok; I’d like to say it makes sense but it doesn’t really - compilers often have their quirks.