[Ngspice-users] what's that mean?? " extern struct comm spcp_coms[]; "

[l <zho...@16...>]

In  ngspice 26 plus version, there is an expression in file

../src/frontend/command.h, line 5: extern struct comm spcp_coms[];
but the variable "spcp_coms " is defined and initialized  in ../src/frontend/command.c
and also it's finded in ../src/main.c,  line 189: extern struct comm spcp_coms[];
and  in ../src/sharedspice ,line 169 extern struct comm spcp_coms[];
and so on.
there are other similar situations, my gcc is 4.9.4, it's compilation termination with  error: array type has incomplete element type。
how does the original source code has compiled ??  should it be declarated :extern struct comm *spcp_coms;?