Script Embedded SQLite With TCL

Question

I am writing a C++ application that embeds TCL and for its database operations I am also embedding SQLite in it. I would like to be able to do the following:

Write TCL scripts for the embedded SQLite from the embedded TCL interpeter.
Pass an SQLite connection from the embedded TCL interpreter to C++ and use it in C++ for db operations, as well as the other way around.

I would appreciate suggestions.

Do people still use TCL? Also, the question is way to broad. It's effectively your wish list only. — sehe
– sehe, Commented Oct 10, 2017 at 8:51
SQLite's own test suite is partly written in Tcl. See wiki.tcl.tk/2633 for some info on Tcl/SQLite integration. — Colin Macleod
– Colin Macleod, Commented Oct 10, 2017 at 9:01
Thanks @Colin, but I couldn't find any info on the page that could help me. — yaro
– yaro, Commented Oct 10, 2017 at 17:35

Donal Fellows · Accepted Answer · 2017-10-11 05:10:51Z

1

Tcl 8.6 should ship with a build of the SQLite interface, the sqlite3 package. However, there's no (official) way to share a database connection from the package with your C++ code; there's simply no API in the package that you can call from C++ to get the connection. The official workaround is to create another connection from your C++ code and that shouldn't be too onerous unless you're doing weird mixing of things between queries in the two language bindings, a very much not normal use case.

You can hack it by using Tcl_GetCommandInfo() to retrieve, among other things, the Tcl database handle command's ClientData field. That can then be cast to a pointer to a structure whose first field is a sqlite3* handle, much as you'd obtain with sqlite3_open(). Which is messy and fragile. Also, you'd still need to respect the usual rules, such as needing to keep to a single thread. This really isn't what I'd recommend!

answered Oct 11, 2017 at 5:10

Donal Fellows

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yaro Over a year ago

many thanks for your answer. Since I want to embed TCL, my intent is to include only the TCL core code and SQLite code in my project and build then into one exec file. This way I can use SQLite in my C++ code as well as in TCL. Is this achievable?

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