Tyler Sebastian Tyler Sebastian - 2 months ago 22
C++ Question

Using libpq with Visual Studios 2013, Compiling to a DLL

I'm trying to create a .dll with Visual Studios 2013. The project includes libpq functionality.

Per other stackoverflow posts, and other sources I've found on the internet, I've (as far as I'm aware) correctly added the postgres lib and include directories to the project. However, when I go to build the project, it returns a number of "unresolved external symbol" errors.

My paths are

C:\Program Files\PostresSQL\9.3\...
so I have them surrounded by quotation marks in the Additional Library/Include Directory fields. I've included the
libpq-fe.h
header file in the project... I'm just not sure what I'm doing wrong.

Another note, I can compile a test program from the command line using g++ with the -I, -L, and -lpq flags, but I'm not sure how to compile to a .dll from the command line (plus it adds complexity that I just don't want to deal with).

These are the specific errors I'm getting:

1>sql_arma.obj : error LNK2001: unresolved external symbol _PQconnectdb
1>sql_arma.obj : error LNK2001: unresolved external symbol _PQstatus
1>sql_arma.obj : error LNK2001: unresolved external symbol _PQerrorMessage
1>sql_arma.obj : error LNK2001: unresolved external symbol _PQfinish
1>C:\Users\tills13\documents\visual studio 2013\Projects\sql_arma\Release\sql_arma.dll : fatal error LNK1120: 4 unresolved externals


I have, as suggested below, included
#pragma comment(lib, "libpq.lib")
in the source file for my project, I still receive these errors.

Answer

I've successfully compiled the sample program by setting these project properties:

  • Add <pgsql install path>\include and \lib to VC++ Directories->Include and ->Library, correspondingly
  • Add libpq.lib to Linker->Input->Additional dependencies

This is the standard way to reference 3rd-party libs. It's just that they recommend using environment variables for their "base dirs" to avoid patching the project when it's under a VCS.

  • To be able to run the app from VS (both with and without debugging), I also specified PATH=%PATH%;<pgsql install path>\bin in Debugging->Environment since this dir isn't in PATH on my system.
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