Teaching pointers (C) to a Java guy [closed]

Question

I have already looked at this and this, but it does not help me at all.

I am teaching a guy who is something of a Java expert. Unfortunately, due to the mandatory-ness of the university curriculum, he is forced to downgrade himself to learning C. ( I use the word downgrade in a strictly technical sense, no offence meant to people who are fans of C ). The thing is, I am able to get him through the whole C syllabus except for pointers.

More importantly, we want to use pointers inside structs, which are actually declared in a header file. I am teaching him to build sharable c libraries/header files. If you need more details, let me know in the comments, and I can share the code I am using in a repo and so on.

Update 1 - I am also looking at this, but its not very clear to me. I haven't used C in a decade, so all this is a little blurry for me.

Update 2 - getting even more specific, what is really happening in these two lines, that I am putting in the header file. I am defining the samplestruct in the corresponding .c file.

typedef struct samplestructrec *samplestruct;
typedef struct samplestructrec samplestruct;

Answer 1

I'm a bit confused, though, like you, it has been a while since I worked in C.

Confusion (a). Are you putting both those lines in the same header file? They seem to be giving incompatible definitions to samplestructrec.

Confusion (b). I wonder if you are misdiagnosing the problem. You can treat #include just about as you would treat textual inclusion. Is there something in one of the C files that makes it incompatible with the header?

Here is quite a bit on headers. https://www.tutorialspoint.com/cprogramming/c_header_files.htm

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Suppose you say:

typedef struct samplestructrec *samplestruct;

Then later (in a C file) you say

samplestructrec foo

Then foo is a pointer but there is no actual samplestruct yet. You need to use malloc or some equivalent to get foo to point to anything.

On the other hand, if you say

typedef struct samplestructrec samplestruct;

and then later say

samplestructrec boo  

Then boo is an actual struct (a block of bits on the stack).

typedef just names a type. It creates information in the compiler, not in the runtime. In particular, samplestructrec is just a name, not a thing.

Answer 2

A little Hungarian

As @talhaIrfan says, the problem is mostly syntax.

This is what I discovered when I was struggling with pointers, while at university. Other students that I introduced the idea to would start to improve shortly after learning this technique. I have also introduced it in professional environments, where the bug rate subsequently reduced.

You can do a lot to improve syntax by introducing a little Hungarian notation (I do not advocate too much of this, just enough).

You need to be consistent, unambiguous, and clear. It should allow you to read your code more easily.

I always use an underscore to separate the Hungarian notation from the rest of the name. I always append type information to the end of the name (this is consistent with what the C libraries do).

I chose a set of symbols

• _pt for pointers.
• _t for types, this is what the C libraries use.

Examples:

typedef struct samplestructrec *samplestruct_pt_t;
typedef struct samplestructrec  samplestruct_t;
samplestruct_t *samplestruct_pt;

Summary

Always choose good name for you objects, and don't do too much Hungarian. When I was programming in C++, we also had at the beginning of a name p_ for parameters, l_ for local, m_ for a member variable (We did this to avoid name collisions, in retrospect I think that these 3 were not needed. We could have used this. instead of m_). That was it just 5 Hungarian pre/post fixes. You don't need any more, probably less, in a strongly typed language.

Answer 3

I have been teaching Programming classes since some time and my experience is:

1. C/C++ Pointers are a nightmare for programming students - whether they have any Java/C#, etc. experience or not.
2. It's the syntax of the pointers (the terrifying*) which is more difficult for students than its semantics.
3. Every student of Java/C#, etc. knows that variables are stored in the RAM (and they have studied in Intro to Computing about RAM addresses etc. basics)

It's not too much difficult to make non-C/C++ programmers understand about pointers if we take the above points and start from some basic examples like URLs being used to point to web pages etc. It has worked for my case (a great deal), hopefully it will help you and others too.