Dynamic array stack struct C

Question

I have a couple of questions. I have a bit of a hard time understanding this code. What exactly is it doing?

For example:

What does typedef struct dynArrStruct do and why does it have dynArr at the end of it? I know the definition of typedef as "allows to created alias for a known data type" but that is jargon to me. Can someone try to put it in layman terms? Thank you!

Why are there 2 struct variables (a1/a2)?

Link to full code if needed:

http://www.cs.uic.edu/pub/CS211/CS211LectureNotesS13/dynArr.c

typedef struct dynArrStruct
{
    double *location;
    int length;
    int currSize;
} dynArr;

int main (int argc, char**argv)
{
    struct dynArrStruct a1;
    dynArr a2;
    int i;

    //rest of code
}

Sergey Kalinichenko · Accepted Answer · 2013-02-19 01:57:04Z

3

What does typedef struct dynArrStruct do and why does it have dynArr at the end of it?

The typedef creates an alias to a type to save you some typing, or to improve readability. In this particular case, it creates an alias called dynArr for the struct dynArrStruct.

Without a typedef, i.e. with only this

struct dynArrStruct
{
    double *location;
    int length;
    int currSize;
};

you would be forced to write struct dynArrStruct every time you need to declare a variable of that struct's type. With a typedef in place, you can write simply dynArr, and the compiler will interpret it as the struct dynArrStruct for you.

answered Feb 19, 2013 at 1:57

Sergey Kalinichenko

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4 Comments

ShadyBears Over a year ago

So would it be ideal to always typedef every struct?

El Hocko Over a year ago

it is also possible to fully omit the word dynArrStruct in the code, making the expression struct dynArrStruct of course invalid and should replaced with dynArr in main()

Sergey Kalinichenko Over a year ago

@juice Yes, that is correct. In fact, many C programming shops require programmers to typedef every struct they may define, and provide coding standards explaining how the naming of the two should be related. Moreover, C++ does this for you by default - it is sufficient to declare a struct without a typedef, and the name of the struct would become usable without the struct keyword.

ShadyBears Over a year ago

Thanks everyone I really appreciate you all helping me understand this.

Karthik T · Accepted Answer · 2013-02-19 02:00:41Z

2

typedef struct dynArrStruct
{
    double *location;
    int length;
    int currSize;
} dynArr;

Is a short form of two different pieces of code.

// define a struct by name dynArrStruct
struct dynArrStruct
{
    double *location;
    int length;
    int currSize;
}; 

//Example of use
struct dynArrStruct d1;

and

// define an alias to "struct dynArrStruct" called dynArr
typedef struct dynArrStruct dynArr; 


//Example of use
dynArr d2; //whoa so short!

answered Feb 19, 2013 at 2:00

Karthik T

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Comments

autistic · Accepted Answer · 2013-02-19 02:10:08Z

0

In addition to dasblinkenlight's answer,

Why are there 2 struct variables (a1/a2)?

The code presented appears to be an example of poorly modularised code (a1) and well modularised code (a2). The modifications made to a1 are very similar to the modifications made to a2. However, the modifications made to a2 are abstracted out into functions (lines 53-55 correspond to the lines found in init, 57-58 correspond to the lines found in push and push), so that that functionality can be easily reused. An example of this reuse is lines 69-72.

answered Feb 19, 2013 at 2:10

autistic

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