How do I open a URL from C++?
Your question may mean two different things:
1.) Open a web page with a browser.
#include <windows.h>
#include <shellapi.h>
...
ShellExecute(0, 0, L"http://www.google.com", 0, 0 , SW_SHOW );
This should work, it opens the file with the associated program. Should open the browser, which is usually the default web browser.
2.) Get the code of a webpage and you will render it yourself or do some other thing. For this I recommend to read this or/and this.
I hope it's at least a little helpful.
EDIT: Did not notice, what you are asking for UNIX, this only work on Windows.
Use libcurl, here is a simple example.
EDIT: If this is about starting a web browser from C++, you can invoke a shell command with system
on a POSIX system:
system("<mybrowser> http://google.com");
By replacing <mybrowser>
with the browser you want to launch.