Undefined refences when compiling example from the documentation

[ldpl]

Undefined refences when compiling example from the documentation

[jtv]

@ldpl what compile options did you use for compiling libpqxx?

[jtv]

This appears to be a duplicate of #820 and #822, but we never got to the bottom of those. :-(

In this case though, your link options seem to be in the wrong order. You did -lpq -lpqxx but the proper order is -lpqxx -lpq.

[ldpl]

I tried compiling with no options, tried with ./configure --disable-shared as in documentation, tried different combinations like ./configure --enable-shared --prefix=/usr CXXFLAGS="-std=c++17", nothing makes any difference.
Swapping -lpqxx and -lpq changes nothing as well.

[jtv]

Thanks @ldpl, that tells us a few things about what the problem isn't. Unfortunately at this point we're left with a mystery, so we'll have to go through the possibilities.

Here's a very basic one: What happens if, on the command line where you compile & link your own application, you put the -lpqxx -lpq part after the name of your source file?

So: g++ example.cpp -lpq -lpqxx

[ldpl]

So: g++ example.cpp -lpq -lpqxx

No idea why but that compiles just fine.

UPD. And so does g++ -fPIC -shared -lpq -lpqxx example.cpp
UPD2. Actually, g++ example.cpp -lpqxx -lpq compiles, not g++ example.cpp -lpq -lpqxx

[tt4g]

This may be due to gcc's behavior.
I found a detailed explanation on Stack Overflow: https://stackoverflow.com/a/409402