all processes on machine have died, roslaunch will exit

用rosbag这个类读取bag包里的数据，程序编译没错，运行的时候报错：

all processes on machine have died, roslaunch will exit

 

std::vector<std::string> topics;

    topics.push_back("/odom");
    topics.push_back("/scan");

之前报错是因为odom和scan前面没加/， 加了以后就没有报错了。

（之前用std:: string scan_topic = "/scan"; topics.push_back(scan_topic);好像也报错）