Question

How is it possible to declare a variable-length array as a global variable ?

when variable length array is declared in a function before the length is scanned, it compiles but does not run. it gives segmentation fault. when the same declaration statement is shifted below the scanning statement, it runs fine.

in case we want a variable length array globally available to all functions, how can we do that? problem here is the that the length of the array can only be scanned through some function only.

Answer 1

You can’t do that.
Here’s what the draft of the standard says:

6.7.6.2 Array declarators

2 If an identifier is declared as having a variably modified type, it
shall be an ordinary identifier (as defined in 6.2.3), have no
linkage, and have either block scope or function prototype scope. If
an identifier is declared to be an object with static or thread
storage duration, it shall not have a variable length array type.

Also,

10 EXAMPLE 4 All declarations of variably modified (VM) types have to be at either block scope or
function prototype scope. Array objects declared with the _Thread_local, static, or extern
storage-class specifier cannot have a variable length array (VLA) type. However, an object declared with
the static storage-class specifier can have a VM type (that is, a pointer to a VLA type). Finally, all
identifiers declared with a VM type have to be ordinary identifiers and cannot, therefore, be members of
structures or unions.