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Circular file

Posted on 2006-07-24
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Last Modified: 2013-11-20
Hi everybody,
I need to write a file that i want to limit the size to 800 Kb and when have this size, start to write from the top of the file and
deleting this first line and so on.
How can i do it.

Thanks.
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Question by:SalvaThor
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3 Comments
 
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Expert Comment

by:reidy_boy
ID: 17177076
Store your data in an array first.  Declare an array of that size in your program.  Write to the array and starting at the beginning when you get to the end.  When you are ready to write the file, just reference the array.
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snyp earned 375 total points
ID: 17186047
why not just keep track of how much you've written to the file and then fseek() your file when you hit your limit?

however.. let's say you're at position 0xC7FFF and you want to write 0x1000 bytes.. try the following..
you'll need to know the size of the data you're writing obviously..

#define SIZELIMIT 0xC8000
char dataArray[512];
unsigned long dataSize;
unsigned long writeSize;
unsigned long filePos;

..

filePos = ftell(filePtr);

if (filePos + dataSize >= SIZELIMIT) {

writeSize = dataSize - ((filePos + dataSize) % SIZELIMIT); // write as much as we can up to the end of the 800kb
fwrite(&dataArray[0], writeSize, 1, filePtr);

fteek(filePtr, 0, 0); // back to the start of the file
fwrite(&dataArray[((filePos + dataSize) % SIZELIMIT)], dataSize - writeSize, filePtr); // write the remainder at 0

}

else
fwrite(&dataArray[0], dataSize, 1, filePtr); // data is small enough to fit, just write it all
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Expert Comment

by:snyp
ID: 17186065
i'm sorry, i need to correct the code there..

fseek(filePtr, 0, 0); // back to the start of the file
fwrite(&dataArray[writeSize], dataSize - writeSize, filePtr); // write the remainder at 0
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