Fix small warnings

[kenji-miyake]

I fixed some warnings.

I put the before/after results below.
Note There are some errors left, so I ignored some options.

  add_compile_options(-Wall -Wextra -Wpedantic -Wno-overflow -Wno-deprecated-declarations -Wno-switch)

Before(aa937b7)

~/ghq/github.com/ros-drivers/usb_cam ros2*
❯ colcon build --symlink-install --cmake-args -DCMAKE_BUILD_TYPE=Release -DCMAKE_EXPORT_COMPILE_COMMANDS=ON 
Starting >>> usb_cam 
--- stderr: usb_cam                              
/home/kenji/ghq/github.com/ros-drivers/usb_cam/src/usb_cam.cpp:126:3: warning: multi-line comment [-Wcomment]
  126 |   //     "mjpeg2rgb " << len << ", image 0x" << std::hex << (unsigned long int)RGB \
      |   ^
/home/kenji/ghq/github.com/ros-drivers/usb_cam/src/usb_cam.cpp:172:3: warning: multi-line comment [-Wcomment]
  172 |   //   rclcpp::get_logger("usb_cam"), "sw scaler " << xsize << " " << ysize << " " \
      |   ^
In file included from /home/kenji/ghq/github.com/ros-drivers/usb_cam/src/usb_cam.cpp:31:
/home/kenji/ghq/github.com/ros-drivers/usb_cam/include/usb_cam/usb_cam.hpp: In constructor ‘usb_cam::UsbCam::UsbCam()’:
/home/kenji/ghq/github.com/ros-drivers/usb_cam/include/usb_cam/usb_cam.hpp:167:20: warning: ‘usb_cam::UsbCam::image_’ will be initialized after [-Wreorder]
  167 |   camera_image_t * image_;
      |                    ^~~~~~
/home/kenji/ghq/github.com/ros-drivers/usb_cam/include/usb_cam/usb_cam.hpp:148:8: warning:   ‘bool usb_cam::UsbCam::is_capturing_’ [-Wreorder]
  148 |   bool is_capturing_;
      |        ^~~~~~~~~~~~~
/home/kenji/ghq/github.com/ros-drivers/usb_cam/src/usb_cam.cpp:63:1: warning:   when initialized here [-Wreorder]
   63 | UsbCam::UsbCam()
      | ^~~~~~
/home/kenji/ghq/github.com/ros-drivers/usb_cam/src/usb_cam.cpp: In member function ‘bool usb_cam::UsbCam::mjpeg2rgb(char*, int, char*, int)’:
/home/kenji/ghq/github.com/ros-drivers/usb_cam/src/usb_cam.cpp:122:63: warning: unused parameter ‘NumPixels’ [-Wunused-parameter]
  122 | bool UsbCam::mjpeg2rgb(char * MJPEG, int len, char * RGB, int NumPixels)
      |                                                           ~~~~^~~~~~~~~
/home/kenji/ghq/github.com/ros-drivers/usb_cam/src/usb_cam.cpp: In member function ‘bool usb_cam::UsbCam::init_device(int, int, int)’:
/home/kenji/ghq/github.com/ros-drivers/usb_cam/src/usb_cam.cpp:738:7: warning: suggest parentheses around operand of ‘!’ or change ‘&’ to ‘&&’ or ‘!’ to ‘~’ [-Wparentheses]
  738 |   if (!stream_params.parm.capture.capability & V4L2_CAP_TIMEPERFRAME) {
      |       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/kenji/ghq/github.com/ros-drivers/usb_cam/src/usb_cam.cpp: In member function ‘bool usb_cam::UsbCam::set_v4l_parameter(const string&, const string&)’:
/home/kenji/ghq/github.com/ros-drivers/usb_cam/src/usb_cam.cpp:1083:1: warning: no return statement in function returning non-void [-Wreturn-type]
 1083 | }
      | ^
In file included from /opt/ros/galactic/include/rclcpp/client.hpp:40,
                 from /opt/ros/galactic/include/rclcpp/callback_group.hpp:23,
                 from /opt/ros/galactic/include/rclcpp/any_executable.hpp:20,
                 from /opt/ros/galactic/include/rclcpp/memory_strategy.hpp:25,
                 from /opt/ros/galactic/include/rclcpp/memory_strategies.hpp:18,
                 from /opt/ros/galactic/include/rclcpp/executor_options.hpp:20,
                 from /opt/ros/galactic/include/rclcpp/executor.hpp:36,
                 from /opt/ros/galactic/include/rclcpp/executors/multi_threaded_executor.hpp:26,
                 from /opt/ros/galactic/include/rclcpp/executors.hpp:21,
                 from /opt/ros/galactic/include/rclcpp/rclcpp.hpp:156,
                 from /home/kenji/ghq/github.com/ros-drivers/usb_cam/include/usb_cam/usb_cam.hpp:51,
                 from /home/kenji/ghq/github.com/ros-drivers/usb_cam/include/usb_cam/usb_cam_node.hpp:32,
                 from /home/kenji/ghq/github.com/ros-drivers/usb_cam/src/usb_cam_node.cpp:30:
/home/kenji/ghq/github.com/ros-drivers/usb_cam/src/usb_cam_node.cpp: In member function ‘void usb_cam::UsbCamNode::get_params()’:
/home/kenji/ghq/github.com/ros-drivers/usb_cam/src/usb_cam_node.cpp:178:39: warning: format ‘%s’ expects argument of type ‘char*’, but argument 5 has type ‘const string’ {aka ‘const std::__cxx11::basic_string<char>’} [-Wformat=]
  178 |       RCLCPP_WARN(this->get_logger(), "Invalid parameter name: %s", parameter.get_name());
      |                                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/kenji/ghq/github.com/ros-drivers/usb_cam/src/usb_cam_node.cpp:178:65: note: format string is defined here
  178 |       RCLCPP_WARN(this->get_logger(), "Invalid parameter name: %s", parameter.get_name());
      |                                                                ~^
      |                                                                 |
      |                                                                 char*
In file included from /home/kenji/ghq/github.com/ros-drivers/usb_cam/include/usb_cam/usb_cam.hpp:32,
                 from /home/kenji/ghq/github.com/ros-drivers/usb_cam/include/usb_cam/usb_cam_node.hpp:32,
                 from /home/kenji/ghq/github.com/ros-drivers/usb_cam/src/usb_cam_node.cpp:30:
/home/kenji/ghq/github.com/ros-drivers/usb_cam/include/usb_cam/usb_cam_utils.hpp: At global scope:
/home/kenji/ghq/github.com/ros-drivers/usb_cam/include/usb_cam/usb_cam_utils.hpp:339:13: warning: ‘bool usb_cam::yuyv2rgb(char*, char*, int)’ defined but not used [-Wunused-function]
  339 | static bool yuyv2rgb(char * YUV, char * RGB, int NumPixels)
      |             ^~~~~~~~
/home/kenji/ghq/github.com/ros-drivers/usb_cam/include/usb_cam/usb_cam_utils.hpp:329:13: warning: ‘bool usb_cam::mono102mono8(char*, char*, int)’ defined but not used [-Wunused-function]
  329 | static bool mono102mono8(char * RAW, char * MONO, int NumPixels)
      |             ^~~~~~~~~~~~
/home/kenji/ghq/github.com/ros-drivers/usb_cam/include/usb_cam/usb_cam_utils.hpp:70:12: warning: ‘int usb_cam::xioctl(int, int, void*)’ defined but not used [-Wunused-function]
   70 | static int xioctl(int fd, int request, void * arg)
      |            ^~~~~~
---
Finished <<< usb_cam [10.6s]

Summary: 1 package finished [10.7s]
  1 package had stderr output: usb_cam

After

~/ghq/github.com/ros-drivers/usb_cam fix-small-warnings*
❯ colcon build --symlink-install --cmake-args -DCMAKE_BUILD_TYPE=Release -DCMAKE_EXPORT_COMPILE_COMMANDS=ON 
Starting >>> usb_cam 
Finished <<< usb_cam [4.61s]                     

Summary: 1 package finished [4.72s]

[flynneva]

@kenji-miyake awesome stuff here! looks great so far, I'll let the CI run and do a more in depth look early tomorrow.

I think this might tackle a lot (maybe all) of the warnings referenced by #152 as well?

[kenji-miyake]

@flynneva Thank you!

I think this might tackle a lot (maybe all) of the warnings referenced by #152 as well?

Unfortunately, no. They were ignored here.

  add_compile_options(-Wall -Wextra -Wpedantic -Wno-overflow -Wno-deprecated-declarations -Wno-switch)

They were avcodec_register_all, avpicture_alloc, and other av-related warnings.
Since it's a bit difficult for me, not in the scope of this PR.