Eigen模板结构体调用cast()方法编译报错求助

编译包含Eigen库的C++代码时遇到模板相关编译错误，同时代码存在main函数拼写错误、ring_rot_offset类型不匹配问题，目标是通过自定义模板结构体的cast方法转换Eigen容器数值类型。

源码（mag_models.cpp） #

#include <iostream>
#include "Eigen/Core"
#include "Eigen/Geometry"


using namespace std;
using namespace Eigen;


template <typename T>
struct CoilCalibrationModel
{
    double global_gain;
    Eigen::Vector3<T> noise;
    Eigen::Vector3<T> bias;
    Eigen::Vector3<T> gain;
    Eigen::Vector3<T> per_channel_gain;
    Eigen::Vector3<T> sensor_offset;
    Eigen::Quaternion<T> sensor_rot_offset;
    Eigen::Vector3<T> ring_offset;
    Eigen::Quaternion<T> ring_rot_offset;
    Eigen::Quaternion<double> base_sensor_offset;
    Eigen::Quaternion<double> base_sensor_rot_offset;
    array<double, 3> crosstalk;

    template<typename U> CoilCalibrationModel<U> cast() const
    {
        CoilCalibrationModel<U> model;
        model.global_gain = U(global_gain);
        model.noise = noise.cast<U>();
        model.bias = bias.cast<U>();
        model.gain = gain.cast<U>();
        model.per_channel_gain = per_channel_gain.cast<U>();
        model.sensor_offset = sensor_offset.cast<U>();
        model.sensor_rot_offset = sensor_rot_offset.cast<U>();
        model.ring_offset = ring_offset.cast<U>();
        model.ring_rot_offset = ring_rot_offset.cast<U>();
        model.base_sensor_offset = base_sensor_offset.cast<U>();;
        model.base_sensor_rot_offset = base_sensor_rot_offset.cast<U>();;
        model.crosstalk = {T(crosstalk[0]), T(crosstalk[1]), T(crosstalk[2])};
        return model;
    }
};

int mian(){
    CoilCalibrationModel<double> fram;
    fram.global_gain= 0.5;
    fram.noise = Eigen::Vector3<double>(1,2,3);
    fram.bias = Eigen::Vector3<double>(1,2,3);
    fram.gain = Eigen::Vector3<double>(1,2,3);
    fram.per_channel_gain = Eigen::Vector3<double>(1,2,3);
    fram.sensor_offset = Eigen::Vector3<double>(1,2,3);
    fram.sensor_rot_offset = Eigen::Quaternion<double>(1,2,3,4);
    fram.ring_offset = Eigen::Vector3<double>(1,2,3);
    fram.ring_rot_offset = Eigen::Vector3<double>(1,2,3);
    fram.base_sensor_offset = Eigen::Quaternion<double>(1,2,3,4);
    fram.base_sensor_rot_offset = Eigen::Quaternion<double>(1,2,3,4);
    fram.crosstalk ={1.0,2.0,3.0};
    cout<<" before cast :"<<fram.global_gain<<endl;
    CoilCalibrationModel<int> framcast = fram.cast<int>();
    cout<<" after cast :"<<framcast.global_gain<<endl;
}

CMake配置文件 #

cmake_minimum_required (VERSION 3.8)

project ("mag-inverse")

set(CMAKE_BUILD_TYPE RelWithDebInfo)

Find_Package(Eigen3 REQUIRED)
Find_Package(Ceres REQUIRED COMPONENTS SuiteSparse EigenSparse Multithreading LAPACK)
include_directories(${CERES_INCLUDE_DIRS})
include_directories(${EIGEN3_INCLUDE_DIRS})


find_package(gflags REQUIRED)
include_directories(.)
add_executable(magtest mag_models.cpp)
target_link_libraries(magtest ${CERES_LIBRARIES})
target_link_libraries(magtest gflags)

编译错误信息 #

error: expected primary-expression before ‘>’ token
   31 |   model.noise = noise.cast<U>();
      |                             ^
/home/xx/AuraTest/mag_models.cpp:31:31: error: expected primary-expression before ‘)’ token
   31 |   model.noise = noise.cast<U>();
      |                               ^
/home/xx/AuraTest/mag_models.cpp:32:27: error: expected primary-expression before ‘>’ token
   32 |   model.bias = bias.cast<U>();
      |                           ^
/home/xx/AuraTest/mag_models.cpp:32:29: error: expected primary-expression before ‘)’ token
   32 |   model.bias = bias.cast<U>();

环境信息 #

• gcc/g++ 版本：9.4
• Eigen版本：3.4

问题修复方案 #

1. 模板成员函数调用需显式声明template
   在模板类的成员函数中调用Eigen的cast<U>()模板方法时，编译器无法自动推导cast是模板函数，必须在调用前添加template关键字，例如将noise.cast<U>()修改为noise.template cast<U>()，所有Eigen容器的cast调用都需要做此修改。

2. 修正main函数拼写错误
   将int mian()改为int main()。

3. 修正ring_rot_offset类型不匹配
   结构体中ring_rot_offset的类型是Eigen::Quaternion<T>，但main函数中用Eigen::Vector3<double>赋值，需改为Eigen::Quaternion<double>类型赋值：fram.ring_rot_offset = Eigen::Quaternion<double>(1,2,3,4);。

4. 移除多余分号
   删除model.base_sensor_offset = base_sensor_offset.cast<U>();;和model.base_sensor_rot_offset = base_sensor_rot_offset.cast<U>();;中的多余分号。

5. 补充缺失的头文件
   代码中使用了array但未包含<array>头文件，需添加#include <array>。

修复后的完整代码 #

#include <iostream>
#include <array>
#include "Eigen/Core"
#include "Eigen/Geometry"

using namespace std;
using namespace Eigen;

template <typename T>
struct CoilCalibrationModel
{
    double global_gain;
    Eigen::Vector3<T> noise;
    Eigen::Vector3<T> bias;
    Eigen::Vector3<T> gain;
    Eigen::Vector3<T> per_channel_gain;
    Eigen::Vector3<T> sensor_offset;
    Eigen::Quaternion<T> sensor_rot_offset;
    Eigen::Vector3<T> ring_offset;
    Eigen::Quaternion<T> ring_rot_offset;
    Eigen::Quaternion<double> base_sensor_offset;
    Eigen::Quaternion<double> base_sensor_rot_offset;
    array<double, 3> crosstalk;

    template<typename U> CoilCalibrationModel<U> cast() const
    {
        CoilCalibrationModel<U> model;
        model.global_gain = U(global_gain);
        model.noise = noise.template cast<U>();
        model.bias = bias.template cast<U>();
        model.gain = gain.template cast<U>();
        model.per_channel_gain = per_channel_gain.template cast<U>();
        model.sensor_offset = sensor_offset.template cast<U>();
        model.sensor_rot_offset = sensor_rot_offset.template cast<U>();
        model.ring_offset = ring_offset.template cast<U>();
        model.ring_rot_offset = ring_rot_offset.template cast<U>();
        model.base_sensor_offset = base_sensor_offset.template cast<U>();
        model.base_sensor_rot_offset = base_sensor_rot_offset.template cast<U>();
        model.crosstalk = {U(crosstalk[0]), U(crosstalk[1]), U(crosstalk[2])};
        return model;
    }
};

int main(){
    CoilCalibrationModel<double> fram;
    fram.global_gain= 0.5;
    fram.noise = Eigen::Vector3<double>(1,2,3);
    fram.bias = Eigen::Vector3<double>(1,2,3);
    fram.gain = Eigen::Vector3<double>(1,2,3);
    fram.per_channel_gain = Eigen::Vector3<double>(1,2,3);
    fram.sensor_offset = Eigen::Vector3<double>(1,2,3);
    fram.sensor_rot_offset = Eigen::Quaternion<double>(1,2,3,4);
    fram.ring_offset = Eigen::Vector3<double>(1,2,3);
    fram.ring_rot_offset = Eigen::Quaternion<double>(1,2,3,4);
    fram.base_sensor_offset = Eigen::Quaternion<double>(1,2,3,4);
    fram.base_sensor_rot_offset = Eigen::Quaternion<double>(1,2,3,4);
    fram.crosstalk ={1.0,2.0,3.0};
    cout<<" before cast :"<<fram.global_gain<<endl;
    CoilCalibrationModel<int> framcast = fram.cast<int>();
    cout<<" after cast :"<<framcast.global_gain<<endl;
}

内容的提问来源于stack exchange，提问作者Soar