# Unit 4: Unable to find 'topic\_ex/Age.h' **URL:** \ **Category:** ROS Basics In 5 Days (C++)\ **Created:** [March 12, 2024, 4:49pm UTC](https://get-help.theconstruct.ai/t/unit-4-unable-to-find-topic-ex-age-h/29393 "2024-03-12T16:49:19Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![arnab007](https://get-help.theconstruct.ai/letter_avatar_proxy/v4/letter/a/e99b99/32.png) [@arnab007](https://get-help.theconstruct.ai/u/arnab007)\ **Post date:** [March 12, 2024, 4:49pm UTC](https://get-help.theconstruct.ai/t/unit-4-unable-to-find-topic-ex-age-h/29393/1 "2024-03-12T16:49:19Z")
Hello, While trying to publish to the custom message `Age`, I have run into a problem. First of all, I have already successfully compiled a separate package to hold the custom message `Age`, as can be attributed by the below console output: ```auto user:~$ rosmsg list | grep Age topic_ex/Age ``` When I try to publish to a custom topic using this custom message (see code below), I see that the IDE is able to locate the `Age.h` header file (that had been generated earlier when I had compiled the package containing the custom message). ```auto #include #include #include #include #include // Include the custom message types // https://people.eng.unimelb.edu.au/pbeuchat/asclinic/software/ros_define_and_use_custom_message_types.html #include "topic_ex/Age.h" using namespace std; int main(int argc, char **argv) { // Initialize a ros-node ros::init(argc, argv, "rosbot_age_node"); // Initialize a publisher to publish the time ros::NodeHandle nh; ros::Publisher pub = nh.advertise("/rob_age", 1000); // At what rate should data be steamed into the new topic ros::Rate loop_rate(2); // Initialize a age-type variable to hold the data in topic_ex::Age rob_age; // Initialize the sub-variables with 0 rob_age.days = 0; rob_age.months = 0; rob_age.years = 0; // A temp variable to hold the time from rosbot unsigned long int temp_time = 0; while (ros::ok()) { // Convert the time appropriately for their respective fields for Age // message rob_age.days = temp_time / 60; // For minutes rob_age.months = rob_age.days / 60; // For hours rob_age.years = rob_age.months / 24; // For days // Publish the message pub.publish(rob_age); ros::spinOnce(); loop_rate.sleep(); ++temp_time; } return 0; } ``` However, when I tried to compile the publisher package, I got the following error on console: ```auto [93%] Built target topic_ex_generate_messages /home/user/catkin_ws/src/age_publisher_pkg/src/publish_age.cpp:9:10: fatal error: topic_ex/Age.h: No such file or directory 9 | #include "topic_ex/Age.h" | ^ ~~~~~~~~~~~~~~~ compilation terminated. make[2]: *** [age_publisher_pkg/CMakeFiles/publish_age.dir/build.make:63: age_publisher_pkg/CMakeFiles/publish_age.dir/src/publish_age.cpp.o] Error 1 make[1]: *** [CMakeFiles/Makefile2:528: age_publisher_pkg/CMakeFiles/publish_age.dir/all] Error 2 make: *** [Makefile:141: all] Error 2 Invoking "make -j8 -l8" failed ``` , which is strange because the IDE affirmed that the header file exists at the mentioned location. I realized later that maybe the CMake file needs to know that it should include the custom-message package `topic_ex`. So I made the following `CMakeList`: ```auto cmake_minimum_required(VERSION 3.0.2) project(age_publisher_pkg) # In package.xml, you have to state them as build_depend. find_package(catkin REQUIRED COMPONENTS roscpp std_msgs topic_ex # custom-message package ) catkin_package( ) include_directories( # include ${catkin_INCLUDE_DIRS} ) add_executable(publish_age src/publish_age.cpp) add_dependencies(publish_age ${publish_age_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS}) add_dependencies(publish_age topic_ex_generate_messages_cpp) target_link_libraries(publish_age ${catkin_LIBRARIES} ) ``` With this, the publisher compiled. This unit should be modified to include the following pieces of information: 1. What format should the custom-message header file should be: `#include "topic_ex/Age.h"` → `#include “/.h”, and 2. What changes must be made in the `CMake` file of the custom subscriber: add the `` under `find_package()` and as `build_depend` in the `package.xml` file. This is just for your information. ---
**Author:** ![girishkumar.kannan](https://get-help.theconstruct.ai/user_avatar/get-help.theconstruct.ai/girishkumar.kannan/32/6994_2.png) [@girishkumar.kannan](https://get-help.theconstruct.ai/u/girishkumar.kannan)\ **Post date:** [March 13, 2024, 3:54am UTC](https://get-help.theconstruct.ai/t/unit-4-unable-to-find-topic-ex-age-h/29393/2 "2024-03-13T03:54:52Z")
Hi @arnab007 , I think your `include` statement syntax is wrong. The line you have is: > [@arnab007](#): > > `#include "topic_ex/Age.h"` But it should be: ```cpp #include ``` You need to use angle brackets (chevrons) and not double quotes. I hope this fixes your issue. Regards, Girish ---
**Author:** ![arnab007](https://get-help.theconstruct.ai/letter_avatar_proxy/v4/letter/a/e99b99/32.png) [@arnab007](https://get-help.theconstruct.ai/u/arnab007)\ **Post date:** [March 13, 2024, 1:04pm UTC](https://get-help.theconstruct.ai/t/unit-4-unable-to-find-topic-ex-age-h/29393/3 "2024-03-13T13:04:04Z")
Hello Girish, Thanks for your reply. Regarding your suggestion, you will find ([link](https://s3.eu-west-1.amazonaws.com/notebooks.ws/cpp_for_robotics/unit2.html?AWSAccessKeyId=AKIAJLU2ZOTUFJRMDOAA&Signature=X6hWuA8166H5zL1ZKZqLYj1kua8%3D&Expires=1710349115#Code-explanation)) that both approaches are valid for their respective use-cases. This is outlined in the free TheConstruct course `C++ for Robotics`, Unit 1, right after the end of `End of Exercise 1.1`. Regards, Arnab ---
**Author:** ![bayodesegun](https://get-help.theconstruct.ai/user_avatar/get-help.theconstruct.ai/bayodesegun/32/10684_2.png) [@bayodesegun](https://get-help.theconstruct.ai/u/bayodesegun)\ **Post date:** [March 14, 2024, 12:03pm UTC](https://get-help.theconstruct.ai/t/unit-4-unable-to-find-topic-ex-age-h/29393/4 "2024-03-14T12:03:31Z")
Perhaps you are trying to do something that is ahead of the unit, because this concept is thought later in the course. Were you asked to create your node in a new package or the same package (`topic_ex`) where you have `Age.msg`? That makes a world of difference. If you need to use a (custom) message from another package, it’s of course necessary to include that package as a dependency, preferrably when creating the package: ```auto cd ~/catkin_ws/src catkin_create_pkg my_new_pkg roscpp pkg_with_custom_msg ``` ---
**Author:** ![arnab007](https://get-help.theconstruct.ai/letter_avatar_proxy/v4/letter/a/e99b99/32.png) [@arnab007](https://get-help.theconstruct.ai/u/arnab007)\ **Post date:** [March 14, 2024, 1:54pm UTC](https://get-help.theconstruct.ai/t/unit-4-unable-to-find-topic-ex-age-h/29393/5 "2024-03-14T13:54:11Z")
Hello bayodesegun, So, the only reason I tried that was because the example output was for a package named `topic_ex`. I was half-way through adding the message as part of another package when I came across the text-in-red `Note`. Hence, I tried following the intended example as closely as possible. No point in trying something new with this concept if I can’t even get the associated example to work. Regards, Arnab ---
**Author:** ![bayodesegun](https://get-help.theconstruct.ai/user_avatar/get-help.theconstruct.ai/bayodesegun/32/10684_2.png) [@bayodesegun](https://get-help.theconstruct.ai/u/bayodesegun)\ **Post date:** [March 15, 2024, 9:44am UTC](https://get-help.theconstruct.ai/t/unit-4-unable-to-find-topic-ex-age-h/29393/6 "2024-03-15T09:44:39Z")
> [@arnab007](#): > > the text-in-red `Note` What does the note say? ---
**Author:** ![system](https://get-help.theconstruct.ai/uploads/default/original/2X/9/9d3ce8305cc0d0d9b6e07d15767a6f245c526f1b.jpeg) [@system](https://get-help.theconstruct.ai/u/system)\ **Post date:** [March 20, 2024, 9:45am UTC](https://get-help.theconstruct.ai/t/unit-4-unable-to-find-topic-ex-age-h/29393/7 "2024-03-20T09:45:30Z")
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