Variable-length array in C

Question

Is it possible to declare a variable when initializing an array?

For example:

#include <stdio.h>

main()
{
    int x;
    int arr[x];
    
    scanf("%i", &x);
}

Or perhaps something similar?

Any help would be appreciated.

Programs in C are sequential. At a time of arr definition it does not know about the future value of x. — Eugene Sh.
– Eugene Sh., Commented Apr 16, 2021 at 19:44

Vlad from Moscow · Accepted Answer · 2021-04-16 20:26:59Z

1

In general you may write

int x;
scanf("%i", &x);
int arr[x];

In this case the array arr will be a variable size array. The value of x shall be greater than 0.

Otherwise in this case

int x;
int arr[x];

the variable x is uninitialized (because it is a variable with automatic storage duration) and as a result the array declaration invokes undefined behavior.

edited Apr 16, 2021 at 20:26

answered Apr 16, 2021 at 19:47

Vlad from Moscow

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R.. GitHub STOP HELPING ICE Over a year ago

OP should note that, as written, this is an exploitable stack overflow bug.

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