constructing variable name from a variable in c++

Question

I have lots of arrays with different sizes so they can't be multidimensional array as far as i know, so i named them as follows:

arr1[]
arr2[]
arr3[]
arr4[]
...

now can i use for loop to go over them and access them...

for(int i=1; i<5; i++) {
    for(int j=o; i<etc; j++) {
     cout<<arr[i][[j]<<endl;
    }
}
or cout<<arr+i<<endl;

now this obviously is telling compiler to add arr and i together, but that is not what i want. I want it to print arr1, arr2, etc.

I have tried, putting dot, comma, slashes, etc.

because using array is the requirment, however, is it possible to put all arrays of different sizes into vector — Muhammad Umer
– Muhammad Umer, Commented Sep 23, 2014 at 14:54
Yes, you can put arrays in arrays by heap allocating them and using pointers — Alexander Meißner
– Alexander Meißner, Commented Sep 23, 2014 at 14:55
@MuhammadUmer - because using array is the requirment, You do know that vector uses a dynamic array internally, right? The internal array can be accessed very easily. So what's the actual reason why you can't use vector? — PaulMcKenzie
– PaulMcKenzie, Commented Sep 23, 2014 at 15:03

Lightness Races in Orbit · Accepted Answer · 2014-09-23 14:52:53Z

4

No. You do need an array here. More specifically, you need a heterogenous container.

With the magic of indirection, you can actually use a homogenous container at the C++ level to achieve these semantics:

std::vector<std::vector<WhateverYourTypeIs>> v;

If you really need only five in the outer array, this will do the job:

std::array<std::vector<WhateverYourTypeIs>, 5> a;

and will simplify your code.

answered Sep 23, 2014 at 14:52

Lightness Races in Orbit

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1 Comment

Lightness Races in Orbit Over a year ago

@Galik: Right, and the OP said "I have lots of arrays with different sizes". That means different types. Granted, now that I'm introducing indirection (via vector) I suppose it's not really heterogenous any more, in the strictest sense.

Community · Accepted Answer · 2017-05-23 11:57:17Z

3

If you are really forced to use plain arrays (and only then), consider using an array of pointers too:

int* const array[] = {arr1, arr2, arr3, arr4, ...};

Thus, you get a pointer to the first element of array arr# with array+#.

You might want a companion-array storing the element counts, too:

size_t carray[] = {sizeof arr1/sizeof *arr1, sizeof arr1/sizeof *arr2,
    sizeof arr1/sizeof *arr3, sizeof arr1/sizeof *arr4, ...};

Also, look at this for a safer way to get the element-count of an array:

template<size_t N, class T>
constexpr size_t element_count(T (&arr)[N])
{return N;}

edited May 23, 2017 at 11:57

CommunityBot

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answered Sep 23, 2014 at 15:03

Deduplicator

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Comments

Alexander Meißner · Accepted Answer · 2014-09-23 14:54:50Z

0

You are confusing compile/build time and runtime. I would suppose to use only runtime objects like arrays/vectors.

But you could also use macros or variable argument lists: http://www.cprogramming.com/tutorial/c/lesson17.html

answered Sep 23, 2014 at 14:54

Alexander Meißner

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