How to use setenv() to export a variable in c++?

Question

I need to export several variables such that they look like the following in the command line

export ROS_HOSTNAME=xxx

How do I use setenv()

Answer 1

Do like this:

setenv("ROS_HOSTNAME", "xxx", true);

---

Note it's synopsis as well:

#include 

int setenv(const char *envname, const char *envval, int overwrite);

See this link for more details on setenv().