fmt-eigen

A header-only formatter function customized for the Eigen library.

Why fmt

The fmt library offers several advantages over traditional methods of formatting and printing data in C++. In this chapter, we will explore why fmt is preferred for these tasks.

Easy to Format

With fmt, formatting and printing data becomes simple and intuitive. Using the fmt::print function, you can easily format output by providing values and placeholders within the format string.

Type-Safe and Type-Free Printing

fmt supports a wide range of data types, making it type-safe and eliminating the need for explicit format specifiers. It automatically handles the formatting based on the provided arguments.

Fast Print Performance

fmt is highly optimized for speed, often surpassing the performance of cout by more than 10 times. Its efficient implementation and utilization of modern techniques contribute to its superior performance.

Usage

Copy the header file fmt_eigen.h to your project or copy to the fmt library path

sudo cp ./fmt_eigen.h /usr/local/include/fmt

Include the header file fmt_eigen.h in your code

#include "fmt_eigen.h"

Then you can easily print Eigen types with fmt::print function

    fmt::print("Matrix:\n{}\n vector:\n{}\n", matrix, vec);

Control the printing precision:

    fmt::print("Matrix:\n{0:.3f}\n vector:\n{1:.4f}\n", matrix, vec); // Specify precision of 4

and also support the block, Diagonal, Transpose functions.

    fmt::print("Matrix Transposed:\n{:.4f}\n", transposed); // Specify precision of 4
    fmt::print("Matrix col or row:\n{:.4f}\n", matrix.col(0)); // Specify precision of 4
    fmt::print("Matrix Bolck:\n{}\n", matrix.block<1,1>(0,0)); // Specify precision of 4
    fmt::print("Matrix Diagonal:\n{}\n", matrix.diagonal()); // Specify precision of 4

Take advantage of the colorful printing inherent to fmt::print:

    fmt::print(fg(fmt::color::steel_blue), "Matrix:\n{}\n vector:\n{}\n", matrix, vec);
    fmt::print(bg(fmt::color::lime_green)|fg(fmt::color::indian_red),
               "Matrix:\n{0:.3f}\n vector:\n{1:.4f}\n", matrix, vec);
    fmt::print(fg(fmt::color::gold)|fmt::emphasis::blink, "Matrix Transposed:\n{:.4f}\n", transposed);
    fmt::print(fg(fmt::color::steel_blue)|fmt::emphasis::bold, "Matrix Transposed:\n{:.4f}\n", transposed);

For more details and examples, please refer to the example.cpp file and the user guide of fmt at https://hackingcpp.com/cpp/libs/fmt.html.

Install fmt

There are three ways to include libfmt in your project.

Use with ROS and catkin

For ROS users (tested with ROS Noetic), the easiest way to install fmt is by installing rosfmt:

sudo apt-get install ros-noetic-rosfmt

To link fmt in your project, there are two ways provided. The first way is to use catkin:

find_package(catkin REQUIRED COMPONENTS
        roscpp
        rosfmt)
include_directories(${catkin_INCLUDE_DIRS})
add_executable(example example.cpp)
target_link_libraries(example
        ${catkin_LIBRARIES}
)

The second way is to use pure CMake:

set(rosfmt_DIR /opt/ros/noetic/share/rosfmt/cmake)
find_package(rosfmt REQUIRED)
include_directories(${rosfmt_INCLUDE_DIRS})
add_executable(example example.cpp)
target_link_libraries(example
  ${rosfmt_LIBRARIES}
)

ROS-free

For non-ROS users, you can install libfmt using the following commands:

sudo add-apt-repository universe
sudo apt update
sudo apt install libfmt-dev

Alternatively, you can download the source code and compile it:

git clone https://github.com/fmtlib/fmt.git
cd fmt
mkdir build
cd build
cmake ..
make
sudo make install

To add libfmt to your project's CMakelists.txt, use the following:

find_package(fmt REQUIRED)
add_executable(example example.cpp)
target_link_libraries(example
        fmt::fmt
)