Value greater than 10^5 in 2d array was not declared in scope

Question

When I tried:
int global[10000][10000];
it works but when
int global[100000][100000];
when I try to access it it gives me error:

global was not declared in the scope.

Any answers ?

Here is my test code:

#include<iostream>
#include<bits/stdc++.h>

int global[100000][100000];
using namespace std;

int main(){
    int i=0;
    while(i<=10){
        cout << global[i][i];
        i++;
    }
    return 0;
}

`#include` -- Visual C++ has no such header. Get rid of it and use the proper `#include` files. — PaulMcKenzie, Jan 11 '19 at 12:33
`int global[100000][100000]` is going to take about 37 Gigabytes of memory on most systems, so I guess that's the problem. Your computer likely doesn't have that much RAM, and even if it does, it probably couldn't allocate that much nevertheless. Still, the error message seems puzzling. — Blaze, Jan 11 '19 at 12:33
Take some time to think about how much memory `100000 * 100000 * sizeof(int)` would take. Do your computer have that much memory? In a *contiguous* block? — Some programmer dude, Jan 11 '19 at 12:34
And please read [Why should I not #include ?](https://stackoverflow.com/questions/31816095/why-should-i-not-include-bits-stdc-h) — Some programmer dude, Jan 11 '19 at 12:35
I get a linker error from your code, unless I declare the `global` as static, like this `static int global[100000][100000];` — Duck Dodgers, Jan 11 '19 at 12:35
What problem are you really trying to solve with using such a large array? Is this going to be an [XY Problem](http://xyproblem.info/)? — PaulMcKenzie, Jan 11 '19 at 12:36
@LightnessRacesinOrbit: OP does not have the rep to upvote it yet. :) — P.W, Jan 11 '19 at 12:39

score 1 · Answer 1 · answered Jan 11 '19 at 13:25

I tried reproducing the error in g++ 8.2.0 but it produces a different but linker error:

/tmp/cceGsEkP.o: In function `__static_initialization_and_destruction_0(int, int)':
temp.cxx:(.text+0x60): relocation truncated to fit: R_X86_64_32 against `.bss'
temp.cxx:(.text+0x6f): relocation truncated to fit: R_X86_64_32 against `.bss'

Above function is responsbile for allocation of static memory before main. Since array is allocated memory contiguously int global[10000][10000] may be possible because of memory requirement of around 300MB, but

Instead, you can:

Try to reduce dimension which will require you to remove redundant information which will not be used in further computation.
If you can't reduce the dimension but won't use all the states then you can use something like std::map.

score 0 · Accepted Answer · answered Jan 11 '19 at 13:22

0

I have the impression you want to show the ten first entries on the diagonal of a very large matrix. Why do you even want to do that?

As you just need about 10 numbers, you can easily create a single-dimensioned matrix int global[10].
Your matrix is so extremely large that it consumes your whole memory, as already mentioned in the comment of Blaze.
Why do you call that variable global? What are you trying to achieve?

answered Jan 11 '19 at 13:22

Dominique

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no just using for testing nothing else, using this name wont create a problem i think. does it ? – Nitish Jan 11 '19 at 13:29
No. I don't think that the usage of `global` as a name for a variable can be of harm in C++. – Dominique Jan 11 '19 at 13:37

Value greater than 10^5 in 2d array was not declared in scope

2 Answers2