Will C++ exceptions safely propagate through C code?

I have a C++ application that calls SQLite's (SQLite is in C) sqlite3_exec() which in turn can call my callback function implemented in C++. SQLite is compiled into a static library.

If an exception escapes my callback will it propagate safely through the C code of SQLite to the C++ code calling sqlite3_exec()?

Solution 1:

My guess is that this is compiler dependent. However, throwing an exception in the callback would be a very bad idea. Either it will flat-out not work, or the C code in the SQLite library will be unable to handle it. Consider if this is some code in SQLite:

{
  char * p = malloc( 1000 );
  ...
  call_the_callback();  // might throw an exception
  ...
  free( p );
}

If the exception "works", the C code has no possible way of catching it, and p will never be freed. The same goes for any other resources the library may have allocated, of course.

Solution 2:

There is already a protocol for the callback to abort the API call. From the docs:

If an sqlite3_exec() callback returns non-zero, the sqlite3_exec() routine returns SQLITE_ABORT without invoking the callback again and without running any subsequent SQL statements.

I'd strongly recommend you use this instead of an exception.

Solution 3:

SQLite is expecting you to return a SQLITE_ABORT on error and a 0 return code for no error. So you ought to wrap all your C++ callback in a try catch. Then in the catch return a SQLite SQLITE_ABORT error code, otherwise a zero.

Problems will occur if you bypass returning through SQLite as it will not free up/complete whatever code it does after you return back from your callback. This will cause untold problems potentially some of which maybe very obscure.