C++ Define elements of array outside function

Question

I am quite new to C++, so if there is a easier way to get what I want, feel free to tell me...

I've got a header containing constants I need to include everywhere in my code to use them in equations. Stuff like temperature and pressure.. Before I was using a single object with a constant mass.

real massObject          = 7.35619e-25;

Now I want to have more than one mass to be able to use more objects. So I tried to define Elements of an array I created.

const int numObjects     = 1;
double vmassObject[numObjects];
vmassObject[0]           = 7.35619e-25;

Then I found out that it was not possible to define every Element outside a function but I don't want to use a function because I would have to call it everytime. Also passing is no option. Is there a way to define the elements globally?

Thanks

You can in fact declare this array inside a function as static, so that it will be initialized only once throughout the lifetime of your program (and not every time the function is called). You can further pass an input argument to the function, telling it which element in the array you want it to return. Thus, you keep this array encapsulated under a narrow interface, with an access level of your choice (here, I have described a simple interface with read-only access level). In addition, if you want to optimize furthermore, you can declare the function inline. — barak manos
– barak manos, Commented Nov 10, 2016 at 15:02

Some programmer dude · Accepted Answer · 2016-11-10 14:48:34Z

2

You can initialize the array:

double vmassObject[numObjects] = {
    7.35619e-25
};

On a related note, you can't put this in a header file that you include in multiple source files. That's because then the array would be defined multiple times, and you can only have one definition in a program.

In the header you can declare the array:

extern double vmassObject[numObjects];

Then put the definition (with the initialization) in a single source file.

answered Nov 10, 2016 at 14:48

Some programmer dude

411k36 gold badges420 silver badges655 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

TK_B Over a year ago

Thanks! Initialising works, but is not great of course. When i put the definition in a source file it has to be in a function again, which I don't want or am I missing something?

Some programmer dude Over a year ago

@TK_B Yes it seems you are missing something, but I don't know what. If you copy-paste the definition as shown in my answer you can put it in the global scope of any source file. Remember to define (and initialize) the size constant first.

coppereyecat Over a year ago

Wouldn't #IFNDEF resolve using the same header file in multiple files?

Some programmer dude Over a year ago

@dwllama Header include guards only protect against multiple inclusion in a single translation unit.

coppereyecat Over a year ago

@Someprogrammerdude Thanks for the reply. I'm involved with a project that uses #ifndef a lot, but I see I have more to learn about how it works before I am sure to use it correctly. :)

Collectives™ on Stack Overflow

C++ Define elements of array outside function

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related