1
2   curl_off_t explained
3   ====================
4
5curl_off_t is a data type provided by the external libcurl include headers. It
6is the type meant to be used for the curl_easy_setopt() options that end with
7LARGE. The type is 64bit large on most modern platforms.
8
9Transition from < 7.19.0 to >= 7.19.0
10-------------------------------------
11
12Applications that used libcurl before 7.19.0 that are rebuilt with a libcurl
13that is 7.19.0 or later may or may not have to worry about anything of
14this. We have made a significant effort to make the transition really seamless
15and transparent.
16
17You have have to take notice if you are in one of the following situations:
18
19o Your app is using or will after the transition use a libcurl that is built
20  with LFS (large file support) disabled even though your system otherwise
21  supports it.
22
23o Your app is using or will after the transition use a libcurl that doesn't
24  support LFS at all, but your system and compiler support 64bit data types.
25
26In both these cases, the curl_off_t type will now (after the transition) be
2764bit where it previously was 32bit. This will cause a binary incompatibility
28that you MAY need to deal with.
29
30Benefits
31--------
32
33This new way has several benefits:
34
35o Platforms without LFS support can still use libcurl to do >32 bit file
36  transfers and range operations etc as long as they have >32 bit data-types
37  supported.
38
39o Applications will no longer easily build with the curl_off_t size
40  mismatched, which has been a very frequent (and annoying) problem with
41  libcurl <= 7.18.2
42
43Historically
44------------
45
46Previously, before 7.19.0, the curl_off_t type would be rather strongly
47connected to the size of the system off_t type, where currently curl_off_t is
48independent of that.
49
50The strong connection to off_t made it troublesome for application authors
51since when they did mistakes, they could get curl_off_t type of different
52sizes in the app vs libcurl, and that caused strange effects that were hard to
53track and detect by users of libcurl.
54
55SONAME
56------
57
58We opted to not bump the soname for the library unconditionally, simply
59because soname bumping is causing a lot of grief and moaning all over the
60community so we try to keep that at minimum. Also, our selected design path
61should be 100% backwards compatible for the vast majority of all libcurl
62users.
63
64Enforce SONAME bump
65-------------------
66
67If configure doesn't detect your case where a bump is necessary, re-run it
68with the --enable-soname-bump command line option!
69