initializer element is not constant - avr gcc - c

Question

I have a simple code of seven segment deceleration :
#include<avr/io.h>
#include<util/delay.h>
int dp=1<<0;
int a=1<<1;
int b=1<<2;
int c=1<<3;
int d=1<<4;
int e=1<<5;
int f=1<<6;
int g=1<<7;
int ss[]={
a|b|c|d|e|f,
b|c,
a|b|g|e|d,
a|b|g|c|d,
f|g|b|c,
a|f|g|c|d,
a|f|g|c|d|e,
a|b|c,
a|b|c|d|e|f|g,
a|b|c|d|f|g,
0x00
};
int main()
{
while(1){}
}
But this gives me error when I am trying to generate .hex from this .c code:
Here is the error:
main.c:12: error: initializer element is not constant
main.c:12: error: (near initialization for 'ss[0]')
...
Same for all element..

Answer 1

Variables with the static storage duration shall be initialized with compile-time constant expressions.
Instead of the set of the variables use an enumeration. For example
#include <stdio.h>
enum
{
dp=1<<0,
a=1<<1,
b=1<<2,
c=1<<3,
d=1<<4,
e=1<<5,
f=1<<6,
g=1<<7
};
int ss[]={
a|b|c|d|e|f,
b|c,
a|b|g|e|d,
a|b|g|c|d,
f|g|b|c,
a|f|g|c|d,
a|f|g|c|d|e,
a|b|c,
a|b|c|d|e|f|g,
a|b|c|d|f|g,
0x00
};
int main(void)
{
return 0;
}

Answer 2

One way to do this is to ensure they are constants (available at compile time), by changing it to:
#define dp 0x01
#define a 0x02
#define b 0x04
#define c 0x08
#define d 0x10
#define e 0x20
#define f 0x40
#define g 0x80
I wouldn't worry too much about making them 1<<n values since the number of times you'll have to change it will be vanishingly small.
Changing them to const int doesn't seem to help. I suspect constexpr would be an ideal solution for this, except for the fact it's C++ :-)
If you have binary constants available to you, you may also want to lokk into something like:
static const int sevenSegMap[] = {
// .abcdefg
0b01111110, // or use 0xfe if no binary constants.
0b00110000,
: and so on
0b01111011,
};