clazarou

Not sure that it matters much, but I'm looking at the 5.1.1 SDK pdf.

1. Within a basic max object's declaration...

typedef struct _simp
{
t_object s_obj;
long s_value;
}
t_simp

What's "t_simp"? I don't think it's a user declared element, but I see that it is being used in the initialization routine's sizeof() to find out the size of _simp. I'd assume it's something explained in one of the header files required for Max/MSP externals, but then I saw the initialization routine for an example with two outlets:

typedef struct _myobject
{
t_object m_ob;
void *m_outlet1;
void *m_outlet2;
}
t_myobject;

... with "t_myobject" seemingly being used in the same capacity as "t_simp". Both are the struct name of the user's choice plus a t in front, so I think I don't understand something fundamental about this syntax.

2. Within the simp object's initialization routine...

int main()
{
t_class *c;

c = class_new("simp", (method)simp_new, (method)NULL, size_of(t_simp), 0L, 0);

//methods here...

}

... I see a pointer named "c" of type "t_class" pointing to... where? If it's not made clear by my questions, I'm currently in an introductory C++ class, my first foray into programming, so I'm used to seeing a pointer given an address through the use of reference operator (&) . I know that the SDK's examples are mostly in C, and I have read through some online tutorial that the reference operator is not required in C, but I would assume I'd still see a line of code directing the pointer somewhere.

3. Also within the initialization routine...

class_addmethod(c, (method)simp_int, "int", A_LONG, 0);

Where can I find the definition of the simp_int method? The basic max object declared for this example is _simp... does this have anything to do with it? Is the method I'm adding with this line of code called "int" or is it "simp_int"?

4. In the new instance routine of the same example

void *simp_new()
{
t_simp *x = (t_simp*)object_alloc(s_simp_class)
}

The tutorial calls s_simp_class a global variable. Is the tutorial using the words variable and pointer interchangeably? And for that matter, class and struct?

5. Finally, in the same example above, how is the asterisk following t_simp interpreted? I'm guessing the parenthesis are being used to force a certain operator precedence, but I would expect the asterisk to be in front of a name of a pointer.

1.  Within a basic max object's declaration...

What's "t_simp"?  I don't think it's a user declared element, but I see that it is being used in the initialization routine's sizeof() to find out the size of _simp.  I'd assume it's something explained in one of the header files required for Max/MSP externals, but then I saw the initialization routine for an example with two outlets:

... with "t_myobject" seemingly being used in the same capacity as "t_simp".  Both are the struct name of the user's choice plus a t in front, so I think I don't understand something fundamental about this syntax.

2.  Within the simp object's initialization routine...

...  I see a pointer named "c" of type "t_class" pointing to... where?  If it's not made clear by my questions, I'm currently in an introductory C++ class, my first foray into programming, so I'm used to seeing a pointer given an address through the use of reference operator (&) .  I know that the SDK's examples are mostly in C, and I have read through some online tutorial that the reference operator is not required in C, but I would assume I'd still see a line of code directing the pointer somewhere.

3.  Also within the initialization routine...

Where can I find the definition of the simp_int method?  The basic max object declared for this example is _simp... does this have anything to do with it?  Is the method I'm adding with this line of code called "int" or is it "simp_int"?

4.  In the new instance routine of the same example

The tutorial calls s_simp_class a global variable.  Is the tutorial using the words variable and pointer interchangeably?  And for that matter, class and struct?

5.  Finally, in the same example above, how is the asterisk following t_simp interpreted?  I'm guessing the parenthesis are being used to force a certain operator precedence, but I would expect the asterisk to be in front of a name of a pointer.

five-fun-questions-about-the-sdks-simple-max-object-example

these are not C-specific things; you would (and actually, will) do the mentioned things the same way in C++ and in C. In fact, you should think about C++ just as an extension to C (by object orientation etc), but the really low-level language elements are (at least in an everyday-usage sense) the same. That said, you might want interesting for example this page:

There you'll find a detailed answer for almost any question regarding the basic language concepts of C or C++. I try to give a fast answer to your questions, though.

 is the name of your newly defined type. From that point on in the code, if one calls for a type 

, the compiler will know that the developer is actually thinking on a 

 member. The same applies for the other type definition called in your example 

 will point to a block in the memory returned by 

. Remember, a pointer is a variable that points to an arbitrary address in the memory. Therefore there are two basic ways in C/C++ to assign a value to a pointer: one is to get the address of an already existing variable (with the reference operator), the other is to request a block of (currently) free memory (usually from the operating system) and tell the pointer to point to that block. This happens typically when you need to store data whose size is determined at run-time level (that is, you can't guess it when you compile your code) like arrays etc. (in fact, this occurs in c++ when you allocate memory with the 

 keyword). And this happens when you call 

 is declared somewhere above this call. I don't know whether you were taking this example from a file or from a code fragment. If the latter, the authors of the file were probably too lazy to provide a full implementation of 

 since at this point you don't need to know what 

 actually does. The method itself is called 

 when you call it in C and it will be triggered when your object receives the 

4. No. Pointer is pointer, variable is variable. Every pointer is a variable (well, except constant pointers), but not every variable is a pointer. For instance, if you declare a variable, let's say 

, then you have a variable, but not a pointer. If you declare instead 

 then you have a variable, which is a pointer. The 

 is a bit more confusing. Since the Max SDK is in C, you don't have classes. But Max itself defines the concept of obex-based externals, which is a kind of 'home made' object-oriented paradigm that Max uses, but without using C++ itself. Therefore in Max you're right, you'd call the 

 representing your object your object's obex-class. But this is not the same as a 

 in C++. Also you wouldn't call in the 'Max-SDK-language' any sort of 

 a class, just usually those ones which represent an object.

5. Since there are two asterixes in that line, it is unclear that which one causes your problems. But again, have a look at the C-syntax, specially the section talking about pointers and probably you'll figure it out. I remember that I had most of my confusions when I started learning C with the pointers and the memory concepts, but once you get through it (to me that took some time, though), you'll find the whole thing pretty easy.

Hi,
these are not C-specific things; you would (and actually, will) do the mentioned things the same way in C++ and in C. In fact, you should think about C++ just as an extension to C (by object orientation etc), but the really low-level language elements are (at least in an everyday-usage sense) the same. That said, you might want interesting for example this page:

1. t_simp is the name of your newly defined type. From that point on in the code, if one calls for a type t_simp, the compiler will know that the developer is actually thinking on a struct with a t_object and a long member. The same applies for the other type definition called in your example t_myobject.

2. c will point to a block in the memory returned by class_new. Remember, a pointer is a variable that points to an arbitrary address in the memory. Therefore there are two basic ways in C/C++ to assign a value to a pointer: one is to get the address of an already existing variable (with the reference operator), the other is to request a block of (currently) free memory (usually from the operating system) and tell the pointer to point to that block. This happens typically when you need to store data whose size is determined at run-time level (that is, you can't guess it when you compile your code) like arrays etc. (in fact, this occurs in c++ when you allocate memory with the new keyword). And this happens when you call class_new as well.

3. simp_int is declared somewhere above this call. I don't know whether you were taking this example from a file or from a code fragment. If the latter, the authors of the file were probably too lazy to provide a full implementation of simp_int since at this point you don't need to know what simp_int actually does. The method itself is called simp_int when you call it in C and it will be triggered when your object receives the int message in Max.

4. No. Pointer is pointer, variable is variable. Every pointer is a variable (well, except constant pointers), but not every variable is a pointer. For instance, if you declare a variable, let's say char c, then you have a variable, but not a pointer. If you declare instead char * ptr_c then you have a variable, which is a pointer. The struct and class is a bit more confusing. Since the Max SDK is in C, you don't have classes. But Max itself defines the concept of obex-based externals, which is a kind of 'home made' object-oriented paradigm that Max uses, but without using C++ itself. Therefore in Max you're right, you'd call the struct representing your object your object's obex-class. But this is not the same as a class in C++. Also you wouldn't call in the 'Max-SDK-language' any sort of struct a class, just usually those ones which represent an object.

5. Since there are two asterixes in that line, it is unclear that which one causes your problems. But again, have a look at the C-syntax, specially the section talking about pointers and probably you'll figure it out. I remember that I had most of my confusions when I started learning C with the pointers and the memory concepts, but once you get through it (to me that took some time, though), you'll find the whole thing pretty easy.


First of all, thank you times a million. Second of all, I'm still having a difficult time with #5, even after looking through the incredibly helpful c syntax link and doing a little rooting around in others' pointer explanations... nowhere can I find an example of a parenthesis enclosing a type and an asterisk, in that order, in front of a function. My problem was only with the following asterisk.

and so's you don't have to scroll back up, it's within the context of

Since the asterisk is enclosed with type t_simp, I would assume it's operating on t_simp in this line of code, but that doesn't make sense. If it was a pointer to the the object_alloc function, why would it be written this way? Ugh. Looks like this is going to take me "some time" too.

First of all, thank you times a million.  Second of all, I'm still having a difficult time with #5, even after looking through the incredibly helpful c syntax link and doing a little rooting around in others' pointer explanations... nowhere can I find an example of a parenthesis enclosing a type and an asterisk, in that order, in front of a function.  My problem was only with the following asterisk.  

and so's you don't have to scroll back up, it's within the context of 

Since the asterisk is enclosed with type t_simp, I would assume it's operating on t_simp in this line of code, but that doesn't make sense.  If it was a pointer to the the object_alloc function, why would it be written this way? Ugh.  Looks like this is going to take me "some time" too.


Seems like some time spent with a C or C++ reference might help most of your questions at this stage. There are lots of good online ones. I leant most of the basics that way, rather than by taking a course. There may also be some good online forums for asking about this stuff, as the questions aren't specific to the MaxMSP SDK.

None of the above is meant to put you off asking questions here - just pointing to possible sources for better/faster/appropriate answers.

In the above object_alloc returns a pointer of void type and we want to assign the pointer to a pointer of type t_simp *. The (t_simp *) is a cast which tells the compiler to interpret the pointer of type void * as one of type t_simp *.

It may well compile without this cast, and do the right thing (partly depending how strict the compiler settings are), but it's good practice to have it there. To look up more on this you might try googling type casting, pointer casting, casting pointers or something similar..

Yup, I thought I might be pushing it a little with my syntax questions, but at least now I have a better idea of exactly what I need to learn. Thanks guys!

Yup, I thought I might be pushing it a little with my syntax questions, but at least now I have a better idea of exactly what I need to learn.  Thanks guys!

Five fun questions about the SDK's simple Max object example