Related SO question and answer, cross-platform: Cross-platform way of getting temp directory in Python
It's pretty generic.
In Qt5: 
#include <QCoreApplication>
#include <QTemporaryDir>
#include <QDebug>
int main(int argc, char *argv[])
{
    QTemporaryDir dir;
    if (dir.isValid()) {
        // dir.path() returns the unique directory path
        qDebug() << "Path name: " << dir.path() ;
    }
}
Also pretty generic.
In bash (terminal or script): echo $TMPDIR
The /var/folders/ is user-specific because if you run ls -l /var/folders/.../ (right before the -Tmp- directory, you will see that the folder is owned by the logged in user. If another user is logged in, their folder is protected by their permissions/ownership and they won't be able to read/modify another users' data. I suggest looking into unix/linux/mac file and folder permissions if you want to know more.
new-host-2:Applications ThisIsMe$ ls -l /var/folders/cp/cpI9fK8qG3y4x4sedjGIOE+++TI/ 
total 0
drwx------  16 ThisIsMe  staff  544 Jan  6 22:12 -Caches-
drwx------  11 ThisIsMe  staff  374 Jan  6 22:56 -Tmp-
http://www.filepermissions.com/articles/what-are-file-permissions-in-linux-and-mac
https://www.linux.com/tutorials/understanding-linux-file-permissions/