Terminal command in a ROS package is not executed - c++

Question

I have a little problem with a ROS node even if i think that it's mainly a C++ code problem.
What i want to do is using a script that runs in the terminal (Ubuntu 14.04) within a ROS node.
I'm doing this using the system() command code of the C++ language.
This script has to elaborate a .txt file stored locally on my PC; when i use the script by a normal command line method, obviously i have to navigate to the directory where my script lies first, and then i launch the script.
To replying this on my node, i use 2 system() instances to navigate to the directory and then to run the script.
The problem is that it seems that the node "cannot see" the command which tells it to navigate to the correct directory, so, all i can obtain is an error saying: cannot read the text file.
The only way to start the script correctly is to launch the node after i manually navigate to the directory where it lies the script.
I'm posting the code below, maybe I'm writing something bad or there is another problem that i can't see, since i'm a noob in the world of ROS and coding in general. Thank you in advance, i know that maybe it's a stupid question!
Marco
Here it is the code:
int main(int argc, char **argv)
{
ros::init(argc, argv, "heart_rate_monitor");
ros::NodeHandle n;
system("cd ~/home/marco/catkin_ws/src/heart_rate_monitor");
system("get_hrv -R test.txt");
exit(0);
return 0;
}
Note: i tried also without the ~ .
EDIT: now it seems that's running correctly, here it is the code:
int main(int argc, char **argv)
{
ros::init(argc, argv, "heart_rate_monitor");
ros::NodeHandle n;
chdir("/home/marco/catkin_ws/src/heart_rate_monitor");
system("get_hrv -R test.txt >doc.txt");
exit(0);
return 0;
}

Answer 1

Use chdir to change directory. System will create a new shell and execute the cd command. Please refer to this stack overflow post for more information.

Answer 2

As neo pointed out, the first system call is changing the current directory of the system call, but it does not influence the parent's (i.e. your node's) current directory.
But, if I may, you should try to solve this differently. Apart from hardcoding the path being wrong, you generally should not assume to have access to the source folder on runtime (e.g. if you do an install, the source could be anywhere). Instead:
put additional data in a new directory (e.g. 'data')
add an install target
retrieve the runtime path to your package using ros::package::getPath('your_package_name') and use the full path + "/data/test.txt" in your system call