Struct and array

[suzanne_lim]

Hi all,

i have a tyedef struct as following.

typedef union __Checksum
{
	unsigned short sh;
	unsigned char ch[2];
} Chksum;

typedef struct __TXPacket
{
    unsigned char StartData;				
    unsigned char DestinationID;			    
    unsigned char SourceID;			
    unsigned char TotalLength;				
    unsigned char Command;			
    unsigned char Parameter;			
    Chksum Checksum;
} TXPacket;

since it is a typedef, can i do as follow?

TXPacket PacketSend [8];

PacketSend.StartData = 'M';
PacketSend.DestinationID = 'A';
.
.
.
.
.
for (i = 0;i<8;i++)
       PacketSend[i] ;
      //do other things with the data as a normal array

Is PacketSend.StartData = PacketSend [0]?


Thanks

[quzah]

This would be the correct method for accessing the first StartData:

foo = PacketSend[0].StartData;
...
PacketSend[0].StartData = foo;

This doesn't actually do anything:

for (i = 0;i<8;i++)
       PacketSend[i] ;

It's like saying:

for(i=0;i<8;i++)
    5;

No effect.


Quzah.

[suzanne_lim]

hi quzah

for (i = 0;i<8;i++)
       PacketSend[i] ;
      //do other things with the data as a normal array

this part is not important. What i try to ask is whether

PacketSend.StartData == PacketSend [0]?

u said that

foo = PacketSend[0].StartData;

does this means that by doing the following

TXPacket PacketSend [8];

i am creating 8 set of PacketSend instead of treating PacketSend as a array of 8 elements where the 8 elements are the elements of TXPacket struct ? Please clarify it to me as i a little bit confuse.

Thanks

[ILoveVectors]

you are creating 8 of everything in the struct,

struct mystruct
{
     int num;
     char letter;
}TX[8];

means i can do the following


TX[0].num = 1;
TX[1].num = 2;
TX[2].num = 3;
TX[3].num = 4;
TX[4].num = 5;
TX[5].num = 6;
TX[6].num = 7;
TX[7].num = 8;
TX[0].letter = 'a'
TX[1].letter = 'b'
TX[2].letter = 'c'
TX[3].letter = 'd'
TX[4].letter = 'e'
TX[5].letter = 'f'
TX[6].letter = 'g'
TX[7].letter = 'h'



cout << TX[0].num << "\t" << TX[0].letter << endl;

[ILoveVectors]

here i typed up a code that you can actually compile

#include <iostream>

using namespace std;

struct person
{
	int age;
	char fletter;

}people[5];

int main()
{
	for(int i = 0; i != 5; i++)
	{
		people[i].age = i;
		people[i].fletter = char(i+65);
	}
	for(int x = 0; x != 5; x++)
	{
		cout << people[x].age << "\t" << people[x].fletter << endl;
	}
	cin.get();
	return 0;
}

[cwr]

this part is not important. What i try to ask is whether

PacketSend.StartData == PacketSend [0]?

No. PacketSend is an array of struct, not a struct, so PacketSend.StartData doesn't make sense, and your compiler will produce a diagnostic.

On the other hand, PacketSend[0].Startdata is equivalent to *(PacketSend+0).Startdata is equivalent to *(PacketSend).Startdata is equivalent to PacketSend->Startdata. However, in this instance, using PacketSend->Startdata may be a little confusing, since it might lead the reader unfamiliar with the rest of your code to think that PacketSend is a pointer, rather than an array of 8 things.

TXPacket PacketSend [8];

i am creating 8 set of PacketSend instead of treating PacketSend as a array of 8 elements where the 8 elements are the elements of TXPacket struct ? Please clarify it to me as i a little bit confuse.

You are creating an array of 8 structs. Where's the confusion?

P.S. ILoveVectors, this is a C forum, would you not confuse the issue by posting C++ code?

[suzanne_lim]

ooo....ic ic....Now i understand.Thanks everyone.