I need to be able to perform random access I/O against a file, creating a new file if it doesn't exist, or opening as-is (no truncation) if it already exists.

None of the access modes for std.stdio.File seem to allow that. Any usage of the "w" mode causes my code to consider the file empty if it pre-exists (though, it doesn't always actually truncate the disk on file?)

If I was coding in C, I would use open() as it gives more options for access:

http://pubs.opengroup.org/onlinepubs/009695399/functions/open.html

However, I don't see this exposed in phobos anywhere?

On Saturday, 26 March 2016 at 00:10:23 UTC, Chris Williams wrote:
> I need to be able to perform random access I/O against a file, creating a new file if it doesn't exist, or opening as-is (no truncation) if it already exists.
>
> None of the access modes for std.stdio.File seem to allow that. Any usage of the "w" mode causes my code to consider the file empty if it pre-exists (though, it doesn't always actually truncate the disk on file?)
>
> If I was coding in C, I would use open() as it gives more options for access:
>
> http://pubs.opengroup.org/onlinepubs/009695399/functions/open.html
>
> However, I don't see this exposed in phobos anywhere?

The Programming in D book chapter on Files http://ddili.org/ders/d.en/files.html will help. I think the "std.stdio.File struct" section on the same page has what you need. Also, take a look at http://dlang.org/phobos/std_stdio.html#.File.open.

On Saturday, 26 March 2016 at 00:10:23 UTC, Chris Williams wrote:
> None of the access modes for std.stdio.File seem to allow that. Any usage of the "w" mode causes my code to consider the file empty if it pre-exists (though, it doesn't always actually truncate the disk on file?)

Mode "a+" or "r+" for append+read or read+write will do it, same as in C.

> If I was coding in C, I would use open() as it gives more options for access:

This function is in `import core.sys.posix.fcntl;` (the documentation is lax on this but generally when you see a Posix function in C that is #include<x.h>, you can get it in D with `import core.sys.posix.X`.