Containerising C++ code and the Boost library using docker

Question

I have an example script called main.cpp which reads as follows:

#include <boost/regex.hpp>
#include <iostream>
#include <string>

int main() {
    std::string line;
    boost::regex pat( "^Subject: (Re: |Aw: )*(.*)" );

    while (std::cin) {
        std::getline(std::cin, line);
        boost::smatch matches;
        if (boost::regex_match(line, matches, pat))
            std::cout << matches[2] << std::endl;
    }
}

The output should be

Foo
Bar: 4
Bar: 4

It is compiled with g++ -o myprogram main.cpp -lboost_signals

With a dockerfile containing:

# Use an official Ubuntu image as the base image
FROM ubuntu:20.04
# Set the working directory inside the container
WORKDIR /app
# Update apt repository and install build tools and Boost library
RUN apt-get update && apt-get install -y \
    build-essential \
    libboost-all-dev \
    && rm -rf /var/lib/apt/lists/*
# Copy the C++ source code into the container
COPY main.cpp /app/main.cpp
# Compile the program using g++
RUN g++ -o myprogram main.cpp -lboost_signals
# Set the default command to run the compiled program
CMD ["./main"]

The thing is, I'm not convinced this dockerfile is 1) optimal 2) reliable for my needs. How can I improve my dockerfile to further streamline my work? TIA

Further, when running the container, it fails:

docker build -t cpp-boost-example .
[+] Building 33.7s (11/11) FINISHED                                                                                                                                                                                                                                                                                                                                   docker:desktop-linux
 => [internal] load build definition from dockerfile                                                                                                                                                                                                                                                                                                                                  0.0s
 => => transferring dockerfile: 1.16kB                                                                                                                                                                                                                                                                                                                                                0.0s
 => [internal] load metadata for docker.io/library/ubuntu:20.04                                                                                                                                                                                                                                                                                                                       0.4s
 => [internal] load .dockerignore                                                                                                                                                                                                                                                                                                                                                     0.0s
 => => transferring context: 2B                                                                                                                                                                                                                                                                                                                                                       0.0s
 => CACHED [1/7] FROM docker.io/library/ubuntu:20.04@sha256:8e5c4f0285ecbb4ead070431d29b576a530d3166df73ec44affc1cd27555141b                                                                                                                                                                                                                                                          0.0s
 => => resolve docker.io/library/ubuntu:20.04@sha256:8e5c4f0285ecbb4ead070431d29b576a530d3166df73ec44affc1cd27555141b                                                                                                                                                                                                                                                                 0.0s
 => [internal] load build context                                                                                                                                                                                                                                                                                                                                                     0.0s
 => => transferring context: 114B                                                                                                                                                                                                                                                                                                                                                     0.0s
 => [2/7] RUN ln -snf /usr/share/zoneinfo/$CONTAINER_TIMEZONE /etc/localtime && echo $CONTAINER_TIMEZONE > /etc/timezone                                                                                                                                                                                                                                                              0.1s
 => [3/7] RUN apt-get update && apt-get install -y tzdata                                                                                                                                                                                                                                                                                                                             2.7s
 => [4/7] WORKDIR /app                                                                                                                                                                                                                                                                                                                                                                0.0s
 => [5/7] RUN apt-get update && apt-get install -y     build-essential     libboost-all-dev     && rm -rf /var/lib/apt/lists/*                                                                                                                                                                                                                                                       29.8s
 => [6/7] COPY main.cpp /app/main.cpp                                                                                                                                                                                                                                                                                                                                                 0.1s 
 => ERROR [7/7] RUN g++ -o myprogram main.cpp -lboost_signals                                                                                                                                                                                                                                                                                                                         0.5s 
------                                                                                                                                                                                                                                                                                                                                                                                     
 > [7/7] RUN g++ -o myprogram main.cpp -lboost_signals:                                                                                                                                                                                                                                                                                                                                    
0.439 /usr/bin/ld: cannot find -lboost_signals                                                                                                                                                                                                                                                                                                                                             
0.439 collect2: error: ld returned 1 exit status                                                                                                                                                                                                                                                                                                                                           
------
dockerfile:23
--------------------
  21 |     COPY main.cpp /app/main.cpp
  22 |     # Compile the program using g++
  23 | >>> RUN g++ -o myprogram main.cpp -lboost_signals
  24 |     # Set the default command to run the compiled program
  25 |     CMD ["./main"]
--------------------
ERROR: failed to solve: process "/bin/sh -c g++ -o myprogram main.cpp -lboost_signals" did not complete successfully: exit code: 1

"optimal" and "reliable" by what metric? Size? Ability to rebuild in the future? Portability to other base container images? As a start, you probably want to avoid shipping a container image with all of the build tools and dependencies; look into multi-stage builds so you only keep the main binary and any runtime dependencies like boost. — Botje
– Botje, Commented Jan 13 at 12:17
Well yes I’m very inexperienced when it comes to Docker so I’m not sure how exactly to do that. Is there a guide? — jimbob97
– jimbob97, Commented Jan 13 at 12:24
Multi-stage builds are a part of every "docker best practices" guide i've read. I'll just leave you with the official Docker documentation — Botje
– Botje, Commented Jan 13 at 12:26
looks like libboost-all-dev doesn't include boost_signals launchpad.net/ubuntu/focal/amd64/libboost-all-dev/…, signals doesn't exist in modern versions of boost bugs.launchpad.net/ubuntu/+source/boost-defaults/+bug/1876788, you're not using it so why link to it? — Alan Birtles
– Alan Birtles, Commented Jan 13 at 12:39
Use std <regex> library instead of boost. If you need boost for anything more, learn to link it as static library or identify, locate and copy the required dll files; On a typical POSIX system, ldd command could work. — Red.Wave
– Red.Wave, Commented Jan 13 at 15:08

David Maze · Accepted Answer · 2025-01-13 12:39:03Z

2

On the specific build error, the current Boost documentation states:

Linking against the Signals2 library

Unlike the original Boost.Signals library, Boost.Signals2 is currently header-only.

You can search on https://packages.debian.org/ for libboost_signals.so, which is the specific file that -lboost_signals would look for, and it just doesn't exist in Debian stable. So you need to

Update to Boost.Signals2 if you haven't already; and
Remove that -l option.

For compiled languages (like C++) you typically want to use a Docker multi-stage build for your image. The idea is that you can have a first build stage with all of the required tools to build the application, and a second build stage that only contain what's needed to run it. In particular you don't need the C++ compiler in the final image, and build-essential brings along a huge amount of tools and header files.

I'd also typically recommend putting your compiled application in a normal binary directory, like /usr/local/bin, which slightly simplifies running it.

# This is basically what you had originally:
FROM ubuntu:20.04 AS build  # <-- added build-stage name
WORKDIR /app
RUN apt-get update && apt-get install -y \
    build-essential \
    libboost-all-dev \
    && rm -rf /var/lib/apt/lists/*
COPY main.cpp ./
RUN g++ -o myprogram main.cpp  # <-- remove -lboost_signals here
# End of first stage.

# The second stage actually runs the application.
FROM ubuntu:20.04

# If your application does need any C shared libraries to run,
# install these here (*not* -dev versions)
# RUN apt-get update && apt-get install -y libboost-...

# Copy the compiled application binary into the final image
COPY --from=build /app/myprogram /usr/local/bin

# Set the standard image metadata to run it
CMD ["myprogram"]

answered Jan 13 at 12:39

David Maze

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3 Comments

jimbob97 Jan 13 at 13:00

Thank you for your answer. Unfortunately, when I run this I get

jimbob97 Jan 13 at 13:00

``` docker build -t boosttest . -------------------- 1 | # This is basically what you had originally: 2 | # This is basically what you had originally: 3 | >>> FROM ubuntu:20.04 AS build # <-- added build-stage name 4 | WORKDIR /app 5 | RUN apt-get update && apt-get install -y \ -------------------- ERROR: failed to solve: dockerfile parse error on line 3: FROM requires either one or three arguments ```

Botje Jan 13 at 15:36

That looks like a terrible bug in the Docker parser. Remove the comment from the FROM line.

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