Definition of global variables using a non constant initializer

Question

#include 

int i=10;
int j=i;
int main()
{
    printf(\"%d\",j);
}

I get an error stating that initialization element is not a const

Answer 1

The idea behind this requirement is to have all static storage duration object initialized at compile time. The compiler prepares all static data in pre-initialized form so that it requires no additional initializing code at run time. I.e. when the compiled program is loaded, all such variables begin their lives in already initialized state.

In the first standardized version of C language (C89/90) this requirement also applied to aggregate initializers, even when they were used with local variables.

void foo(void)
{
  int a = 5;
  struct S { int x, y; } s = { a, a }; /* ERROR: initializer not constant */
}

Apparently the reason for that restriction was that the aggregate initializers were supposed to be built in advance in the pre-initialized data segment, just like global variables.