write in a vector through the same (ROS) callback using boost::bind (C++)

Question

i'm using ROS topics in order to acquire some image streams from a simulator. the idea is the following: i have "n" visual sensors and i'd like to declare n subscriber (through a for cycle) that read n different topics and call the same callback: passing an integer to the c.b. i'll be able to fill a vector of images (each of them received on a different topic).

this is my code:

vector <IplImage*> Images;

void newImageTrigger_trgI(const sensor_msgs::ImageConstPtr& msg, int i)
{
 cv_bridge::CvImagePtr cv_ptr;

 try
 {

cv_ptr = cv_bridge::toCvCopy(msg, enc::BGR8);

Images[i] = cv_ptr->image;

}
catch (cv_bridge::Exception& e)
{
ROS_ERROR("cv_bridge exception: %s", e.what());
}

}

int main( int argc, char** argv )
{

ros::init(argc, argv, "ImageProcessing");
ros::NodeHandle n;

std::vector<ros::Subscriber> sub;
for (int i = 1; i < 6; i++)
{
string str_i=string_converter(i);
 sub[i] = n.subscribe("/vrep/visionSensorData"+str_i, 1,...   //ERROR
   boost::bind(&newImageTrigger_trgI, _1, i));
 }

  .....

Obviously: "invalid arguments" at //ERROR

can someone help me please?...i think it's something concerning boost::bind function thanks

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Originally posted by mateo_7_7 on ROS Answers with karma: 90 on 2013-06-10

Post score: 0

Answer 1

Good afternoon,

I think I had the same problem you're having and what I did to fix it was substituting this line:

sub[i] = n.subscribe("/vrep/visionSensorData"+str_i, 1, boost::bind(&newImageTrigger_trgI, _1, i));

for this:

sub[i] = n.subscribe <sensor_msgs::ImageConstPtr> ("/vrep/visionSensorData"+str_i, 1, boost::bind(&newImageTrigger_trgI, _1, i));

I think, when you bind the parameter with the boost library you have to specify the type of the callback item to the node handler, but am not sure why.

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Originally posted by t.pimentel with karma: 385 on 2013-06-18

This answer was ACCEPTED on the original site

Post score: 2

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Original comments

Comment by eliasm on 2014-10-07:
This solved the problem for me as well. Thanks!

Answer 2

While the ROS specific stuff looks OK on first glance, it is always helpful to post the full error message instead of just saying "invalid arguments" ;-)

I assume that the way you try to create your string is your main problem. Try

for (int i = 1; i < 6; i++)
{
  std::stringstream topicName;
  topicName << "/vrep/visionSensorData" << i;
  sub[i] = n.subscribe(topicName.str().c_str(), 1, boost::bind(&newImageTrigger_trgI, _1, i));
}

to subscribe to the topics /vrep/visionSensorData1 .. /vrep/visionSensorData6

P.S.: Oh, and look up how to write to a vector (either resize before the loop if you already know the final size, or use push_back() in the loop).

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Originally posted by Philip with karma: 990 on 2013-06-10

This answer was NOT ACCEPTED on the original site

Post score: 1

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Original comments

Comment by mateo_7_7 on 2013-06-11:
you are right! and furthermore: using push_back() i don't need the index, as even the boost::bind function anymore...isn't it?

Comment by Philip on 2013-06-11:
Sounds good. You need the boost::bind if you want to know which subscriber is currently calling the callback, in your case to save the image in the correct position of the Images[]-array, Can you post your final code as an edit to the questions, so others can see the final solution?

Comment by mateo_7_7 on 2013-06-11:
...but if i use the subscribers in order, and so i read the topics in order, automatically i'll have the images stored in the vector in order..am I right? ps. of course...i'm gonna do that, i have to fix some errors

Comment by Philip on 2013-06-11:
The subscribers aren't necessarily called in any order, at least in none that you should rely on. When the callback function is invoked (because a message was received) and some value has to be saved at a specific "position" in your vector, you have to provide that information to the callback.

Comment by mateo_7_7 on 2013-06-11:
Invalid arguments ' Candidates are: ros::Subscriber subscribe(const std::basic_string<char,std::char_traits,std::allocator> &, unsigned int, void (#1::*)(#0), #1 *, const ros::TransportHints &) ros::Subscriber subscribe(ros::SubscribeOptions &) ros::Subscriber subscribe(const std::basic_

Comment by mateo_7_7 on 2013-06-11:
string<char,std::char_traits,std::allocator> &, unsigned int, void (#1::*)(#0)const, #1 , const ros::TransportHints &) ros::Subscriber subscribe(const std::basic_string<char,std::char_traits,std::allocator> &, unsigned int, void (#1::)(const boost::shared_ptr<const #0> &),#

Comment by mateo_7_7 on 2013-06-11:
1 , const ros::TransportHints &)ros::Subscriber subscribe(const std::basic_string<char,std::char_traits,std::allocator> &, unsigned int, void (#1::)(const boost::shared_ptr<const #0> &)const, #1 *, const ros::TransportHints

Comment by mateo_7_7 on 2013-06-11:
the last 3 posts are about the error i receive trying to compile the code you suggested me...??

Comment by mateo_7_7 on 2013-06-11:
the method to create the string is definitely right...it works for others topics.