copying structs

[adev111]

Hi there, I have two structs where I am trying to copy from.

typedef struct {
char *netID[7];
int hopCount;
char *nextHop[2];
}Routers;

Routers one;
Routers two;
I read from file and set one.netID = something, one.hopCount = something and etc

How can I set two the same as one?

Can someone please help, its urgent!!
Thanks

 

[cpjust]

Since you didn't specify what the "something" is that you want to set netID and nextHop to, I'm not sure of the best way to copy it?

From what I see, netID is an array of 7 strings and nextHop is an array of 2 strings. Is that really what you were trying to make?

 

[cdlvj]

typedef struct {           
     char *netID[7];
        int hopCount;                     
        char *nextHop[2];                     
        }ROUTERS;

ROUTERS one;
ROUTERS two;
ROUTERS *three;

// to copy and have two distinct areas with same info
memcpy(&one,&two,sizeof(ROUTERS));

// to have one area of memory with same info
three=&one;

printf("%d",one.hopCount);
printf("%d",three->hopCount);

 

[Diancecht]

He wants to copy from one to two, I guess.

ROUTERS one;
ROUTERS two;

memcpy(&(one.netID),&(two.netID),7*sizeof(char*));

Cheers,
Dian

 

[xwb]

Note that this is a shallow copy. Structure copies are legal in C.

one = two;

 

[dEVooXiAm]

But not for pointers. It is very risky to copy structures with pointers, unless you really know what you're doing

For example, you copy those structures like one = two.
After that, somewhere in code, you call

free(one.netID[1]);
one.netID[1] = NULL;

BUT, two.netID[1] still contains a "valid" pointer to the memory that is now freed. You use the pointer - you get exception! And spend your next 2 days trying to figure out why a "valid" pointer causes an exception

If you're dealing with pointers, always write your own copy routines, so that you allocate seperate memory blocks for pointers.

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When you do it, do it right.