error: ‘_1’ was not declared in this scope

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Hi.

I'm trying to use boost bind in my ROS 2 package. But I'm getting the following error when building with Colcon build:

error:‘_1’ was not declared in this scope

error:‘ _2’ was not declared in this scope

Here is my C++ code:

 #include <functional>
 #include <memory>
 #include "rclcpp/rclcpp.hpp"
 #include "std_msgs/msg/string.hpp"
 #include <message_filters/subscriber.h>
 #include <message_filters/synchronizer.h>
 #include <message_filters/sync_policies/approximate_time.h>
 #include <message_filters/time_synchronizer.h>
 #include "boost/bind/bind.hpp"
 #include <functional>

 void callback(const std_msgs::msg::String::SharedPtr& st_1, 
      const std_msgs::msg::String::SharedPtr& st_2) {
         // Callback function...
 }

 int main(int argc, char** argv){
     rclcpp::init(argc, argv);
     auto node = rclcpp::Node::make_shared("my_node");

     message_filters::Subscriber<std_msgs::msg::String> st_1(node, "st_1");
     message_filters::Subscriber<std_msgs::msg::String> st_2(node, "st_2");
     message_filters::TimeSynchronizer<std_msgs::msg::String, std_msgs::msg::String> sync(st_1, st_2, 10);
     sync.registerCallback(boost::bind(&callback, _1, _2));

    rclcpp::spin(node);

    return 0;
 }

CMakeFile:

 cmake_minimum_required(VERSION 3.5)
 project(project)

 # Default to C99
 if(NOT CMAKE_C_STANDARD)
     set(CMAKE_C_STANDARD 99)
 endif()

 # Default to C++14
 if(NOT CMAKE_CXX_STANDARD)
    set(CMAKE_CXX_STANDARD 14)
 endif()

 if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
      add_compile_options(-Wall -Wextra -Wpedantic)
 endif()

 # find dependencies
 find_package(ament_cmake REQUIRED)
 find_package(rclcpp REQUIRED)
 find_package(std_msgs REQUIRED)
 find_package(message_filters REQUIRED)
 find_package(Boost REQUIRED COMPONENTS 
      system
      filesystem 
      date_time 
      thread
 )

 if(BUILD_TESTING)
     find_package(ament_lint_auto REQUIRED)
     ament_lint_auto_find_test_dependencies()
 endif()

 add_executable(sub src/subscriber.cpp)
 ament_target_dependencies(sub rclcpp std_msgs message_filters)
 target_include_directories(sub PRIVATE ${Boost_INCLUDE_DIRS})
 target_link_libraries(sub ${Boost_LIBRARIES})

 install(TARGETS
     sub
 DESTINATION lib/${PROJECT_NAME})

 ament_package()

Any help is welcome! Thanks!