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Building using CMake

First of all, the libpqxx build requires the full PostgreSQL development package. You must have that package installed before you can build libpqxx.

The instructions will assume that you're working from a command-line shell. If you prefer to work from an IDE, you'll have to know how your IDE likes to do things, and you'll want to follow the shell instructions as a guide.

I'm not too familiar with CMake, and this build relies heavily on contributions from users. If you see something wrong here, please file a bug and explain, in simple words, what needs changing and why.

There are two ways to use libpqxx in your project with CMake:

  • (A) copy and build the libpqxx source tree.
  • Or (B), make use of a separately installed libpqxx.

We'll go through both of these.

Option (A): Copy and build the libpqxx source tree

This option is nice and portable. If you want others to be able to compile your project on their own systems, this method probably requires a bit less setup than the other option. It's easier to keep compatible compilation options between libpqxx and your project.

On the flip side, building your project will take a bit longer, because it will build libpqxx along the way. And of course, you'll need to make sure that there's a copy of the libpqxx tree somewhere. You could do that by having the libpqxx git repo as a submodule inside yours.

As mentioned, you'll need to have the PostgreSQL dev libraries installed on your system, including their headers.

Let's say you have a copy of the libpqxx source tree inside your source tree as deps/libpqxx, and you want to want to build libpqxx in a subdirectory of your build directory called build-pqxx.

Given that, make sure you have a line like this in your CMakeLists.txt:

    add_subdirectory(deps/libpqxx build-pqxx)

You'll also need to mention libpqxx in your target_link_libraries, so that your code will link with libpqxx. For example, if your project is named ausom and links to no other libraries:

    target_link_libraries(ausom PRIVATE pqxx)

So a simple working CMakeLists.txt might be:

cmake_minimum_required(VERSION 3.18)
project(ausom)
add_executable(ausom src/ausom.cxx)
set(CMAKE_CXX_STANDARD 20)

add_subdirectory(deps/libpqxx build-pqxx)
target_link_libraries(ausom PRIVATE pqxx)

Option (B): Make use of a separately installed libpqxx

If libpqxx is already installed, you can just make use of that in your own CMakeLists.txt:

    find_package(libpqxx REQUIRED)

For this to work, there must be a configuration file libpqxxConfig.cmake or libpqxx-config.cmake that CMake can find. If this file exists but CMake can't find it, you may have to set libpqxx_DIR in your CMakeLists.txt to point to a directory containing that configuration file.

You'll also need to mention libpqxx in your target_link_libraries, so that your code will link with libpqxx. For example, if your project is named ausom and links to no other libraries:

    target_link_libraries(ausom PRIVATE pqxx)

So a simple working CMakeLists.txt might be:

cmake_minimum_required(VERSION 3.18)
project(ausom)
add_executable(ausom src/ausom.cxx)
set(CMAKE_CXX_STANDARD 20)

find_package(libpqxx REQUIRED)
target_link_libraries(ausom PRIVATE pqxx)

Of course that does mean that you need libpqxx installed on your system. We'll look into that next.

Installing a libpqxx OS package

Your operating system provider may have a packaged version of libpqxx ready for you to install. For example, on a Debian or Ubuntu system you might run:

    sudo apt-get install libpqxx-dev

But the exact name of the package you need may depend on the system. In a Debian-flavoured system, the -dev suffix is a convention for saying that you want not just a binary library installed, but its header files as well. You definitely need those. On a RedHat-flavoured system, the convention is a suffix of -devel after the name, i.e. libpqxx-devel.

Other systems may conventionally include the headers with the library package. For example, on macOS using HomeBrew, you would just...

    brew install libpqxx

Of course if there is no ready-made libpqxx package for your system, or it's not up to date, or it does not provide a libpqxx-config.cmake configuration file, another option is to build and install libpqxx using CMake.

Building and installing libpqxx yourself

If you just want to get libpqxx itself built and installed quickly, run cmake from the root of the libpqxx source tree. This configures your build.

Then compile libpqxx by running:

    cmake --build .

To install in the default location:

    cmake --install .

The rest of this document will go deeper into the details of this, but you may not need it.

Stages

I'll explain the main build steps in more detail below, but here's a quick rundown:

  1. Configure
  2. Compile
  3. Test
  4. Install
  5. Use

The Test step is optional.

Configure

Run cmake to configure your build. It figures out various parameters, such as where libpq and its headers are, which C++ features your compiler supports, and which options your compiler needs. CMake generates configuration for your build tool: Makefiles for make, or a Solution (".sln") file for MSVC's msbuild, and so on.

At this stage you can also override those options yourself. e.g. to instruct the compiler to look for libpq in a non-standard place, or to use a different compiler, or pass different compiler flags. Don't try to specify those while doing the actual compile; set them once when running cmake.

Let's say $BUILD is the directory where you want to build libpqxx, and $SRC is where its source code is. So for example, the readme file will be at $SRC/README.md.

In the simplest case, you just do:

    cd $BUILD
    cmake $SRC

Add CMake options as needed. There's more about the options below. I'll also explain the two directories.

Cheat sheet

Here are some popular cmake options for libpqxx:

  • -DSKIP_BUILD_TEST=on skips compiling libpqxx's tests.
  • -DBUILD_SHARED_LIBS=on to build a shared library.
  • -DBUILD_SHARED_LIBS=off to build a static library.
  • -DBUILD_DOC=on to build documentation.
  • -DINSTALL_TEST=on to install test executor binary.

On Windows, I recommend building libpqxx as a shared library and bundling it with your application. On other platforms I would prefer a static library.

Building the documentation requires some tools to be installed. It takes at least Doxygen, but there's no list of requirements. The way to get this set up is to just try it and see what it's missing.

Generators

You can also choose your own build tool by telling CMake to use a particular "generator." For example, here's how to force use of make:

    cmake -G 'Unix Makefiles'

Or if you prefer to build using ninja instead:

    cmake -G Ninja

There are many more options. You may prefer yet a different build tool.

Finding libpq

The CMake step tries to figure out where libpq is, using Cmake's find_package function. If that doesn't work, or if you want a libpq in a different location from the one it finds, there are two ways to override it.

The first is to set the individual include and link paths.

To make the build look for the libpq headers in some directory $DIR, add these options:

  • -DPostgreSQL_TYPE_INCLUDE_DIR=$DIR
  • -DPostgreSQL_INCLUDE_DIR=$DIR

To make the build look for the libpq library binary in a directory $DIR, add this option:

  • -DPostgreSQL_LIBRARY_DIR=$DIR

The second, easier way requires CMake 3.12 or better. Here, you specify a path to a full PostgreSQL build tree. You do this (again for some directory $DIR) by simply passing this cmake option: -DPostgreSQL_ROOT=$DIR

Source and Build trees

Where should you run cmake?

Two directories matter when building libpqxx: the source tree (where the libpqxx source code is) and the build tree (where you want your build artefacts). Here I will call them $SRC and $BUILD, but you can call them anything you like.

They can be one and the same, if you like. It's convenient, but less clean, as source code and build artefacts will exist in the same directory tree. If you're going to delete the source tree after installing, of course it's fine to make a mess in there.

Compile

To compile, run:

    cmake --build $BUILD

(Where $BUILD is again the directory where you wish to do the build.)

This command will invoke your build tool. Other ways to do the same thing would be...

  • With Unix Makefiles: make
  • With Ninja: ninja
  • With Visual Studio: msbuild libpqxx.sln
  • etc.

Depending on your build tool, you may want to speed this up by adding an option like -j 16, where 16 is an example of how many processes you might want to run in parallel. The optimal number depends on your available CPUs and memory. If you have enough memory, usually the number of CPUs will be a good starting point for the right number. Don't use this option with Ninja though. It figures things out for itself.

Test

Of course libpqxx comes with a test suite, to check that the library is functioning correctly.

You can run it, but there's one caveat: you need to give it a database where it can log in, without a password or any other parameters, and try out various things.

And when I say you need to "give" it a database, I really mean "give." The test suite will create and drop tables. Those will all have names prefixed with "pqxx", so it's probably safe to use a database you already had, but if any of the items in your database happen to have names starting with pqxx, tough luck. They're fair game.

Enter this in your shell to build and run the tests:

    test/runner

Configuring the test database

But what if you do need a password to log into your test database? Or, what if it's running on a different system so you need to pass that machine's address? What if it's not running on the default port?

You can set these parameters for the test suite, or for any other libpq-based application, using the following environment variables. (They only set default values, so they won't override parameters that the application sets in some other way.)

  • PGHOST — the IP address where we can contact the database's socket. Or for a Unix domain socket, its absolute path on the filesystem.
  • PGPORT — TCP port number on which we can connect to the database.
  • PGDATABASE — the name of the database to which you wish to connect.
  • PGUSER — user name under which you wish to log in on the database.
  • PGPASSWORD — user name's password for accessing the database.

See the full list at https://www.postgresql.org/docs/current/libpq-envars.html

Be careful with passwords, by the way. Depending on your operating system and configuration, an attacker with access to your machine could try to read your password if you set it on the command line:

  • Your shell may keep a log of the commands you have entered.
  • Environment variables may be visible to other users on the system.

If at all possible, rely on postgres "peer authentication." Once set up, it is both more secure and more convenient than passwords.

Install

Once you've built libpqxx, CMake can also help you install the library and headers on your system. The default installation location will vary from one operating system to another, but you can set it explicitly.

Let's say you've got your finished build in $BUILD, and you want to install it to your system's default install location. The command for this is:

    cmake --install $BUILD

But you may want to install to some other location. Let's call it $DEST. $DEST might be something like /usr/local on a Unix-like system, or something like D:\Software on a Windows system.

To install to $DEST, run:

    cmake --install $BUILD --prefix $DEST

Use

Other projects can include libpqxx in their CMake builds.

Here's an example of a CMakeLists.txt fragment. You'll probably still need to provide details specific to your project.

    # (First set LIBVERSION to the libpqxx version you have.)
    set(libpqxxdir "libpqxx-${LIBVERSION}")

    # You can usually skip building the tests.
    set(SKIP_BUILD_TEST ON)

    # On Windows we generally recommend building libpqxx as a shared
    # library.  On other platforms, we recommend a static library.
    IF (WIN32)
        set(BUILD_SHARED_LIBS ON)
    ELSE()
        set(BUILD_SHARED_LIBS OFF)
    ENDIF()

    add_subdirectory(${libpqxxdir})

If you are using shared libraries (which is recommended when building on Windows), you may need to ensure that libpq and the libraries it in turn requires are all in your dynamic link path.