Thread: struct and pointers

Hi,

I am trying to create different messages to be transferred between two hosts. The program structure that I am following is to create a master struct where all the variables to be passed in different messages are declared.
Then I have created different struct for different messages using the same variables from master struct, the values of which I am trying to pass is through pointers.
Below is the rough outline of what I am trying to do. I dont know whether this is the right approach or there is another better way to do it.

The errors that I am getting while compiling are:
1. expression must have a constant value
2. incomplete type is not allowed

Both are pointed when I try to create an instance of message structure and passing the pointers of master struct.

Please help.

Code:

struct Master{

  char  Bulk_Charging_Complete : 1;
  char  Charging_Complete : 1;
  short Vehicle_Energy_Capacity;
  char  Vehicle_RESS_SOC;
  short Vehicle_Maximum_Power_Limit : 13;
  short Vehicle_Maximum_Current_Limit: 13;
  short Vehicle_Maximum_Voltage_Limit: 13;
  short Charger_Maximum_Power_Limit: 13;
  short Charger_Maximum_Current_Limit: 13;
  short Charger_Maximum_Voltage_Limit: 14;
  short Charge_Current_Request: 13;
} Power;


 /* create a pointer of type Master struct and point to instance of that struct type,i.e Power */


struct Master *power_pointer = &Power;     


// creating a structure of a message, the value to its variables will be fetched by pointer to the master structure

struct {
  short var1 : 1;
  char var2 : 4;
  short var3 : 1;
  short var4 : 4;  
}EV_msg_01;

// creating a structure of a message, the value to its variables will be fetched by pointer to the master structure

struct {
  short var1 : 1;
  short var2 : 4;
  short var3 : 1;
  short var4 : 4;  
}station_msg_01;



struct EV_msg  EV_msg_01 = {
                          power_pointer->Vehicle_Energy_Capacity,         
                          power_pointer->Vehicle_RESS_SOC, 
                          power_pointer->Vehicle_Maximum_Power_Limit,     
                          power_pointer->Vehicle_Maximum_Current_Limit
                          };


struct station_msg_01 station_msg_01 = {
                           power_pointer->Charger_Maximum_Power_Limit,  
                           power_pointer->Charger_Maximum_Current_Limit, 
                           power_pointer->Charger_Maximum_Voltage_Limit,  
                           power_pointer->Charge_Current_Request
                          };

Your struct prototype should be placed just after your include files and function prototypes. That way all your other functions have that global proto info on the struct. The structs you actually work on, should be declared in main(), and then passed around via pointers to your other functions.

Inside those other functions, you can now declare pointers to a local struct, if you wish.

What's with the colons? Is this code from Pascal or ???

Change your editor you code with, so it doesn't put tabs into the code - use spaces instead. Your code, as it's displayed on the forum, is almost unreadable. By the time I get to the end of a line of code, the first part of the line, is no longer visible. (This is true with all the programming forums I've been to, btw.)

Thanks Adak and grumpy. Actually this is what is required in our experiment, sending packets consisting of bits,which represents the messages.

I will try to create functions instead of structs and pass the pointers to variables in the master struct.

But again is there any other better way of doing the same thing.

Thanks

Yes, you can use bitfields. But you need to use some logic so the sender place the various fields onto the network in some defined order, and the receiver retrieves those fields in the same order.

So, if I make different struct for each different message and create an instance of them when there is a need to send that particular message, will that be better than the above method of mine. Thanks