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cURL > Development > README.curl_off_t

curl_off_t explained

This contents is from the curl/lib/README.curl_off_t file.

 
   curl_off_t explained
   ====================
 
curl_off_t is a data type provided by the external libcurl include headers. It
is the type meant to be used for the curl_easy_setopt() options that end with
LARGE. The type is 64bit large on most modern platforms.
 
Transition from < 7.19.0 to >= 7.19.0
-------------------------------------
 
Applications that used libcurl before 7.19.0 that are rebuilt with a libcurl
that is 7.19.0 or later may or may not have to worry about anything of
this. We have made a significant effort to make the transition really seamless
and transparent.
 
You have have to take notice if you are in one of the following situations:
 
o Your app is using or will after the transition use a libcurl that is built
  with LFS (large file support) disabled even though your system otherwise
  supports it.
 
o Your app is using or will after the transition use a libcurl that doesn't
  support LFS at all, but your system and compiler support 64bit data types.
 
In both these cases, the curl_off_t type will now (after the transition) be
64bit where it previously was 32bit. This will cause a binary incompatibility
that you MAY need to deal with.
 
Benefits
--------
 
This new way has several benefits:
 
o Platforms without LFS support can still use libcurl to do >32 bit file
  transfers and range operations etc as long as they have >32 bit data-types
  supported.
 
o Applications will no longer easily build with the curl_off_t size
  mismatched, which has been a very frequent (and annoying) problem with
  libcurl <= 7.18.2
 
Historically
------------
 
Previously, before 7.19.0, the curl_off_t type would be rather strongly
connected to the size of the system off_t type, where currently curl_off_t is
independent of that.
 
The strong connection to off_t made it troublesome for application authors
since when they did mistakes, they could get curl_off_t type of different
sizes in the app vs libcurl, and that caused strange effects that were hard to
track and detect by users of libcurl.
 
SONAME
------
 
We opted to not bump the soname for the library unconditionally, simply
because soname bumping is causing a lot of grief and moaning all over the
community so we try to keep that at minimum. Also, our selected design path
should be 100% backwards compatible for the vast majority of all libcurl
users.
 
Enforce SONAME bump
-------------------
 
If configure doesn't detect your case where a bump is necessary, re-run it
with the --enable-soname-bump command line option!

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