Update 2 bits in large files at given offsets. TOUGH?!?!

[IonelBurtan]

I want to update 2 bits in a large file at given offsets.
The big file is 8k paginated, and I also know in what page to make the update (

let us say that the absolute offset is 8196 in page 2 in the 1 Mb file. there i Have two bytes I want to overwrite with ascii characters 0 and 1.

How ca I Do that in VB. I have tried with MapViewOfFile, but I could not managed it to work.

Like that:
hFile = CreateFile...
hMap = CreateViewOfFile
hBaseMemory = MapViewOfFile
...
modify bytes with lstrcpy
...
UnmapViewOfFile hBaseMemory
CloseHandle hMap
CloseHandle hFile


any help apreciated,
tnx

s-)

Blessed is he who in the name of justice and goodwill, sheperds the weak through the valley of darkness...

http://www20.brinkster.com/ionelb

 

[rsinj]

just use the standard VB open/read/write using Binary file type.

see

http://www.tek-tips.com/faqs.cfm?spid=222&newpid=222&sfid=4774

just read up to the point of your absolute offset and get the byte which has the bit you are interested in flipping. update the bit/byte, output it, then continue.

you could probably also do it using Random access mode where you define a record of 1 byte length and then can read/write in place without having to create a new file.

 

[IonelBurtan]

Tnx, I'd like too, But i did not mentioned That I get the hFile from outsite (so the CreateFile call is made outside my code).
So, i think I must use some APIs for this job with HANDLE to the file (the standard write of visual basic does not know windows handles as far as I know).

I looked in WriteFile but I do not know how to write so that I do not increase the size of the file, that is not to make append but update of the bytes in question.

Ionel,
Any ideeas in this...?

s-)

Blessed is he who in the name of justice and goodwill, sheperds the weak through the valley of darkness...

http://www20.brinkster.com/ionelb