What are the functional differences between iODBC and unixODBC?

Question

There are two major Open Source platform independent implementation of the ODBC. It is iODBC and unixODBC.

Considering Unix as ODBC user platform and feature-wise, what are the real practical differences between these two implementations?

Answer 1

Just so you know I use and have contributed to unixODBC and I don't use iODBC.

Unicode support

unixODBC follows MS ODBC Driver manager and has SQLWCHARs as 2 bytes UCS2 encoded. iODBC I believe uses wchar_t (this is based on attempting to support iODBC in DBD::ODBC)

cursor library

unixODBC has one, I don't "think" iODBC has.

application support

A lot of ODBC applications support unixODBC e.g., OpenOffice and ODBC drivers from Oracle, IBM and SAP. I'm not sure about iODBC.

OS support

iODBC has always been the most used on on Macs since Apple included it (although I believe it is removed from Lion). Both can be built from source and most Linux distributions package both (although not Novell/Suse which only distributes unixODBC).

thread safety

unixODBC is thread safe and includes flags to protect handles at different levels. This did not used to be the case with iODBC (but that might have changed now).

support

Both have support forums (unixODBC has 3) although I'd say the unixODBC ones are far more active (I'm on both).

Licensing

unixODBC is GPL and LGPL. iODBC is LGPL/BSD

In practice there is not a lot of difference but I think you'll find unixODBC is more widely used.

Answer 2

I finally found some time for a more complete answer... (attn @mloskot -- you can change your accepted answer, if you agree that this one is more accurate and/or complete than the other)

iODBC and unixOBDC are basically API equivalent, both being cross-platform implementations of Microsoft's ODBC standard. iODBC's flexible Unicode support includes UCS-2, UTF-8, UCS-4. iODBC libraries are bundled into macOS Panther (10.3.0) through Big Sur (11.2.x), and may be built and/or installed on AIX, Solaris, HP-UX, any Linux distribution, *BSD, other Unix-like OS, and more. iODBC has been thread safe for a very long time, and is actively maintained and supported by OpenLink Software (my employer).

The table below covers the most common comparative questions (is there something I should add?), and is based on iODBC 3.52.14, as of February 2021 (reports version 03.52.1421.0217), and unixODBC 2.3.9, as of September 2020.

For a somewhat more detailed comparison, and a much more fancy and detailed table, see this spreadsheet

feature	iODBC	UnixODBC
Unicode support
UCS-2	YES	YES
UCS-4 (a/k/a UTF-32)	YES	NO
UTF-08 (a/k/a UTF-8)	YES	NO
UTF-16	YES	YES
UTF-32 (a/k/a UCS-4)	YES	NO
Supports drivers and apps developed using other SDKs
Supports drivers developed using iODBC SDK	YES	NO
Supports apps developed using iODBC SDK	YES	NO
Supports drivers developed using unixODBC SDK	YES	YES
Supports apps developed using unixODBC SDK	YES	YES
Supports drivers developed using DataDirect SDK	YES	NO
Supports apps developed using DataDirect SDK	YES	NO
OS default DM
macOS	YES	NO
Linux	partial	partial
Unix-like	partial	partial
OS support
macOS	YES	partial
Linux	YES	YES
Unix-like	YES	YES
User-friendly native GUI Administrator
macOS	YES	Qt-based
Linux	GTK-based and HTML-based	Qt-based
Unix-like	GTK-based and HTML-based	Qt-based
Thread Safe	YES	YES
Support
Mailing List(s)	YES	YES
Forum(s)	YES	YES
Github repository	YES	YES
SourceForge repository	YES	YES
Open Source Licensing
GPL	NO	programs
LGPL	YES	libraries
BSD	YES	NO

Notes

Unicode a/k/a Wide Characters

• iODBC supports and translates between all of UCS-2, UCS-4, UTF-8, UTF-16, UTF-32
• unixODBC follows MDAC, and SQLWCHARs are 2 bytes UCS2 encoded

SDK lock-in

• iODBC supports applications and drivers developed using unixODBC SDK and DataDirect SDK as well as those developed using iODBC SDK
• unixODBC only supports applications and drivers developed using unixODBC SDK