• Chris Williams (11/11) Mar 25 2016 I need to be able to perform random access I/O against a file,
• data pulverizer (6/17) Mar 25 2016 The Programming in D book chapter on Files
• Adam D. Ruppe (7/13) Mar 25 2016 Mode "a+" or "r+" for append+read or read+write will do it, same

Chris Williams <yoreanon-chrisw yahoo.co.jp> writes:

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?

data pulverizer <data.pulverizer gmail.com> writes:

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 

Adam D. Ruppe <destructionator gmail.com> writes:

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`.