How to call a function several times, but with a different structure as argument?

Hi

I have written a function where I can save a structure in a file. So the prototype looks like this:

Code:

void SaveStructure(FILE *f, STRUCTURE *structure);

The structure looks for example like this:

Code:

typedef struct { int dummy; char text[30]; } STRUCTURE ;

Now I want to use the function SaveStructure(...) again, but with this structure for example:

Code:

typedef struct { int nr; char name[30]; char street[30]; } NEW_STRUCTURE ;

How can I make it possible that the function SaveStructure(...) doesn't care how the structure looks like?
Does the format of the pointer struct always looks the same? So could I make a dummy-structure:

Code:

typedef struct { int dummy } SAVESTRUCT;

and use the function:

Code:

void SaveStructure(FILE *f, SAVESTRUCT *structure);

this way?

Code:

void main (void) { FILE *f1 = NULL; FILE *f2 = NULL; STRUCTURE structure; NEW_STRUCTURE new_structure; SaveStructure(f1, &structure); SaveStructure(f2, &new_structure); return; }

thx for any help....

Key to this would be what SaveStructure does. Does it store the structure in binary? Or does it write each member to a text file? If it were a binary, I might write it something like this.

Code:

void SaveStructure(FILE *f, void *structure, size_t size);

Code:

SaveStructure(f1, &structure, sizeof structure); SaveStructure(f2, &new_structure, sizeof new_structure);

If it saves to a text file, perhaps have a third parameter that specifies the structure type. Then you can select a proper pointer type.

It will be a binary file. Thx for your answer, I will try it out...

mfg

Jup, that works.

Now I have another problem. In the function, I have to copy the data from one file to another (for example to add a block of data in the middle of the file). For that, I need a temporary structure to carry the block from one file to another. Can I now use a void-pointer too, and for the size of the block, I can use size?

Generally question about the void-pointer:
The void-pointer would be the pointer to the beginning of my block of data or whatever I have. And where's the end of the block? Does the system know, that from where the void-pointer points to till the end of the block, data is stored? So the void-pointer acts like a normal variable and will be freed after the function has been finished?

thx for help again

Quote:

Originally Posted by mabuhay

Now I have another problem. In the function, I have to copy the data from one file to another (for example to add a block of data in the middle of the file). For that, I need a temporary structure to carry the block from one file to another. Can I now use a void-pointer too, and for the size of the block, I can use size?

Yes. I was imagining something like this.

Code:

void SaveStructure(FILE *f, void *structure, size_t size) { fwrite(structure, size, 1, f); }

Quote:

Originally Posted by mabuhay

Generally question about the void-pointer:
The void-pointer would be the pointer to the beginning of my block of data or whatever I have. And where's the end of the block?

I was assuming a wrapper for fread/fwrite, which will copy n items of s bytes. What I did was pass the size of the structure in bytes from the calling function and used this for s. One of these blobs of bytes is the n.

Quote:

Originally Posted by mabuhay

Does the system know, that from where the void-pointer points to till the end of the block, data is stored?

Not exactly.

Quote:

Originally Posted by mabuhay

So the void-pointer acts like a normal variable and will be freed after the function has been finished?

It acts like a normal variable because it is one. I don't think I'd use the term "freed", I'd say it goes out of scope just the same as if you'd passed a copy of where a structure starts as a structure pointer.

Thanks for all your answers. It's running :)