Installing your C library for end users

Every just-makeit project is also a distributable C library.

Prerequisites

The end user needs the following tools — just-makeit itself is not required:

Linux (Debian/Ubuntu):

sudo apt-get install cmake gcc pkg-config

macOS (Homebrew):

brew install cmake pkg-config
# gcc ships with Xcode Command Line Tools: xcode-select --install

Windows (MSYS2/MinGW):

pacman -S mingw-w64-x86_64-cmake mingw-w64-x86_64-gcc mingw-w64-x86_64-pkg-config

Overview

Every just-makeit project ships a lib<project>.so in addition to its Python extensions. The same C code drives both: each component compiles once as a CMake OBJECT library and links into both the Python .so and the combined shared library. End users who don't use Python at all can consume it via the standard mechanisms below.

This applies to all project layouts — standalone objects (just-makeit object), multi-type modules (just-makeit module + just-makeit object --module), or a mix of both.

What gets installed

$PREFIX/
├── include/
│   ├── my_project.h             # umbrella header — include this
│   ├── component_a/
│   │   └── component_a_core.h
│   └── component_b/
│       └── component_b_core.h
├── lib/
│   ├── libmy_project.so         # shared library
│   ├── pkgconfig/
│   │   └── my-project.pc        # pkg-config descriptor
│   └── cmake/my_project/
│       ├── my_project-config.cmake
│       └── my_project-config-version.cmake

Build and install

Set the install prefix before building — cmake bakes the prefix into the generated my-project.pc at configure time.

cmake -S . -B build -DCMAKE_INSTALL_PREFIX=/usr/local
cmake --build build
cmake --install build

For a non-root local install substitute any writable path:

cmake -S . -B build -DCMAKE_INSTALL_PREFIX="$HOME/.local"
cmake --install build

Note: make && make test calls cmake -B build internally with the default prefix. If you ran make first, re-run the cmake -S . line above before installing to regenerate the .pc file with the correct prefix.

Using with pkg-config

pkg-config --cflags --libs my-project   # verify it resolves

Compile a consumer:

gcc $(pkg-config --cflags my-project) \
    consumer.c \
    $(pkg-config --libs my-project) \
    -lm -o consumer

Linux / --as-needed note: Split --cflags and --libs with the source file between them. GNU ld on Debian/Ubuntu uses --as-needed by default, which silently drops any shared library that appears before the object files referencing it. If you merge them with the source last ($(pkg-config --cflags --libs my-project) consumer.c) you will get undefined-reference errors at link time even though the library is present.

If you installed to a non-standard prefix, point pkg-config at it:

export PKG_CONFIG_PATH="$HOME/.local/lib/pkgconfig"

Using with CMake

cmake_minimum_required(VERSION 3.16)
project(my_consumer C)

find_package(my_project REQUIRED)

add_executable(consumer consumer.c)
target_link_libraries(consumer PRIVATE my_project::my_project_lib m)

Configure with the prefix if it's not on the default search path:

cmake -B build -DCMAKE_PREFIX_PATH="$HOME/.local"
cmake --build build

Runtime loading (rpath)

The installed .so is not automatically on the dynamic linker's search path unless you installed to /usr/local (or ran ldconfig after a system-wide install).

For a custom prefix, embed the library path in the binary at link time:

pkg-config:

LIB_DIR=$(pkg-config --variable=libdir my-project)
gcc $(pkg-config --cflags my-project) \
    consumer.c \
    $(pkg-config --libs my-project) \
    -Wl,-rpath,"$LIB_DIR" \
    -lm -o consumer

CMake: set INSTALL_RPATH_USE_LINK_PATH or CMAKE_BUILD_RPATH:

set_target_properties(consumer PROPERTIES INSTALL_RPATH_USE_LINK_PATH ON)

Or pass it on the command line:

cmake -B build \
    -DCMAKE_PREFIX_PATH="$HOME/.local" \
    -DCMAKE_BUILD_RPATH="$HOME/.local/lib"

Alternatively, set LD_LIBRARY_PATH at runtime (useful for quick testing, not for deployment):

LD_LIBRARY_PATH="$HOME/.local/lib" ./consumer

Verifying the install

# headers present
ls $PREFIX/include/my_project.h

# library present and has expected symbols
nm -D $PREFIX/lib/libmy_project.so | grep component_a_create

# pkg-config resolves
pkg-config --modversion my-project