Bag File Reading and Writting Example
## Synopsis
- rosbag file reaing and writting
## C++ Example
### write bag file example
```cpp
#include <ros/ros.h>
#include <rosbag/bag.h>
#include <std_msgs/Int32.h>
#include <std_msgs/String.h>
int main(int argc, char** argv)
{
ros::init(argc, argv, "bag_writer");
ros::NodeHandle nh;
rosbag::Bag bag;
bag.open("test.bag", rosbag::bagmode::Write);
std_msgs::String str;
str.data = std::string("foo");
std_msgs::Int32 i;
i.data = 42;
bag.write("chatter", ros::Time::now(), str);
bag.write("numbers", ros::Time::now(), i);
bag.close();
ros::spinOnce();
return 0;
}
```
### read bag file example
```cpp
#include
#include
#include
#include
#include
#include
#define foreach BOOST_FOREACH
int main(int argc, char** argv)
{
ros::init(argc, argv, "bag_reader");
ros::NodeHandle nh;
rosbag::Bag bag;
bag.open("test.bag", rosbag::bagmode::Read);
std::vector topics;
topics.push_back(std::string("chatter"));
topics.push_back(std::string("numbers"));
rosbag::View view(bag, rosbag::TopicQuery(topics));
foreach (rosbag::MessageInstance const m, view) {
std_msgs::String::ConstPtr s = m.instantiate();
if (s != NULL)
std::cout << s->data << std::endl;
std_msgs::Int32::ConstPtr i = m.instantiate();
if (i != NULL)
std::cout << i->data << std::endl;
}
bag.close();
ros::spinOnce();
return 0;
}
```
# Python Example
## Write bag file
```python
#!/usr/bin/python
# http://wiki.ros.org/rosbag/Code%20API
import rosbag
from std_msgs.msg import Int32, String
bag = rosbag.Bag('test.bag', 'w')
try:
s = String()
s.data = 'foo'
i = Int32()
i.data = 42
bag.write('chatter', s)
bag.write('numbers', i)
finally:
bag.close()
```
## Read bag file
```python
#!/usr/bin/python
# http://wiki.ros.org/rosbag/Code%20API
import rosbag
bag = rosbag.Bag('test.bag')
for topic, msg, t in bag.read_messages(topics=['chatter', 'numbers']):
print(topic)
print(msg)
bag.close()
```
## References
- [rosbag/Code API]\( API?action=fullsearch&context=180&value=linkto%3A"rosbag%2FCode+API")
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