Print out the contents of a string using ROS_INFO

asked 2013-12-09 10:38:59 -0500

JP
95 ●14 ●20 ●27

Hi all,

I have a line such as:

   std_msgs::String s;
s.data = c.c_str(); //same data as above.
pthread_mutex_lock(&send_CS);
tum_ardrone_pub.publish(s);
pthread_mutex_unlock(&send_CS);

What I would like to do is look at the contents of s that is passed into the method publish(). I tried something like:

ROS_INFO("(2) (%s) \n",s.c_str());

But that failed at compile time. Thanks!

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answered 2013-12-09 10:48:01 -0500

roehling
1951 ●25 ●28 ●43 http://www.fkie.fraunhofer.de/

std_msgs::String is not the same thing as std::string and cannot be treated as such; it is a message type that has a std::string member variable called data. Thus, the correct way to output the message string is

ROS_INFO("%s\n", s.data.c_str());

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Thank you!

JP ( 2013-12-09 11:51:13 -0500 )edit

For additional clarification, using ROS_INFO_STREAM uses the ostream operator implementation (operator<<) that rosmsg generates for each message type. The ostream operator is similar to the output you would see from rostopic echo.

mjcarroll ( 2013-12-12 03:05:33 -0500 )edit

Thanks for that!

JP ( 2013-12-12 09:52:31 -0500 )edit

For some reason c_str() didn't work for me so I used data() instead: ROS_INFO("frame: %s", msg.header.frame_id.data()); or in OP case ROS_INFO("%s\n", s.data());