I am writing a conduit that creates a file on an expansion card. I am
running into a strange problem where it seems like the function
VFSFileWrite behaves strangely depending on the number of bytes that
you attempt to write. It appears to be a word boundary issue, but I
cannot determine which boundaries are "good" or "bad" in order to
figure out a work-around. Below is a structure that represents a
single record to be written to the expansion card file:
typedef struct
{
char sku[20];
UINT32 price;
UINT32 descriptionLength;
UINT32 descriptionOffset;
} SkuInfoExpansionCardRecordType;
Here is a code excerpt that shows a single record being written to the
card:
UINT32 numBytesWritten;
SkuInfoExpansionCardRecordType skuInfoRec;
UINT32 recordSize = sizeof(SkuInfoExpansionCardRecordType);
// populate skuInfoRec with appropriate data
result = VFSFileWrite(skuInfoFileRef, recordSize, &skuInfoRec,
&numBytesWritten);
This results in 32 bytes of garbage being written to the expansion
file. After this garbage, the record is correctly written.
If I change the structure to the following:
typedef struct
{
char sku[kSkuLength];
UINT32 price;
UINT32 descriptionLength;
UINT32 descriptionOffset;
UINT32 unused;
} SkuInfoExpansionCardRecordType;
then everything works fine. So, for writing single records, this is
an adequate work-around.
The problem is that I have to create very large expansion card files
and it is not efficient to write each record individually. I write
some number of records to a buffer and then write the buffer to the
card. However, this buffering makes it much harder to predict when
word-boundary issues are going to cause problems.
Has anyone seen this problem before and what was your solution. Thank
you in advance.
Gabe Black
Forall Systems, Inc.
Chicago, IL
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