Cannot set %PATH% in windows from boost::process - c++

Question

I have a program which works great on Linux, but fails to preserve some of %PATH% on Windows. Here's an example:
parent.cpp
#include <boost/process.hpp>
int main()
{
auto this_env = boost::this_process::environment();
boost::process::environment env = this_env; // make a copy to avoid changing the orig
env["TESTVAR"] = "Test12"; // Confirm we can set a variable
env["TESTVAR"] += "Test34"; // Confirm we can append
env["PATH"] += "C:\\Users\\"; // Confirm we can append to PATH
boost::process::child c(
boost::process::exe = "./child.exe",
boost::process::env = env
);
c.wait();
}
child.cpp
#include <boost/process.hpp>
#include <iostream>
int main()
{
auto env = boost::this_process::environment();
std::cout << "TESTVAR = " << env["TESTVAR"].to_string() << std::endl
<< "PATH = " << env["PATH"].to_string() << std::endl;
}
Output on Linux (good):
$ g++ parent.cpp -o parent.exe
$ g++ child.cpp -o child.exe
$ echo PATH = $PATH
PATH = /usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games
$ ./parent.exe
TESTVAR = Test12:Test34
PATH = /usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games:C:\Users\
PATH is augmented! ~~~~~^
Output on Windows (bad):
$ x86_64-w64-mingw32.static.posix-g++ parent.cpp -o parent.exe -lwsock32 -lboost_filesystem-mt-x64
$ x86_64-w64-mingw32.static.posix-g++ child.cpp -o child.exe -lwsock32
$ scp parent.exe child.exe user#windows:
$ ssh user#windows
> echo %PATH%
C:\Windows\system32;C:\Windows;...
> parent.exe
TESTVAR = Test12:Test34
PATH = C:\Users\
^~~~ Path is replaced!
Is this a bug in boost::process, a feature of Windows, or is there something wrong with my code?

Answer 1

There appears some case-sensitivity in windows environment variables. By changing child.cpp to this, we can see all environment variables:
#include <boost/process.hpp>
#include <iostream>
int main()
{
auto env = boost::this_process::environment();
for (auto it : env )
std::cout << it.get_name() << " = " << it.to_string() << std::endl;
}
The output contains:
Path = C:\Windows\system32;C:\Windows;...
TESTVAR = Test12;Test34
PATH = C:\Users\
If we change parent.cpp from :
env["PATH"] += "C:\\Users\\";
to
env["Path"] += "C:\\Users\\";
we get the correct output on Windows:
Path = C:\Windows\system32;C:\Windows;...;C:\Users\
TESTVAR = Test12;Test34
While cmd.exe can set/get path insensitively (SET PATH=%PATH%;C:\\Users\\), the API used by boost is case-sensitive. Strange!