compatible files

Posted on 2002-06-10
Medium Priority
Last Modified: 2012-05-04
I need to have visual basic 6.0 write and read a binary file that can also be read be a c program.
Can anyone provide me with a simple example?
Need to write strings, a character,floating point number, and a structure.

Question by:pentomino
  • 2

Expert Comment

ID: 7067658
Here is an example of reading/writing a binary file.  I have not looked at the code, but it may be helpful.

LVL 22

Accepted Solution

rspahitz earned 400 total points
ID: 7067835
VB can write "binary" files by simply encoding the pieces any way you want.  Then C can read those by unencoding from the same process.

Are you looking for a specific predefined format, like packed decimal or "zip" format?

To write data from VB:

strXXX = "testing"
open "somefile.bin" for output as #1
print #1, strXXX; chrX; dblXXX;
close #1

' resulting file:

Obviously, the extraction will not work well unless you know the length of the string and maybe the type of data, so you would probably want to add something like this:

print #1, chr$(len(strXXX));strXXX;

On the C-end, it would need to understand the style using a mapping mechanism.  It may just be simpler to create an ActiveX control to do all the work and add methods for "CreateFile", "AddItem", "GetItem", etc.

Author Comment

ID: 7067876

Well, I was hoping I would not have to tweak the C code at all.  If I have to modify how it reads the data, I just may go with a text file.

LVL 22

Expert Comment

ID: 7068243
Well, then, find out the format that C is using and write VB code to put it in that format.  I haven't checked out gencross' link, btu maybe that will handle it or get you close.

The only caveat I can see is that the data format may change depending on the O/S.  For example, a 32-bit O/S may write a number as 4 bytes, but a 64-bit O/S may write the same number with 4 additional bytes with all zeros.  This would cause some incompatibility and require some sort of upgrade tool for "old" files being moved to the new O/S.

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