I had a problem related to OCI8 and XAMPP for days in a row, the problem was shown as:
Fatal error: Call to undefined function oci_connect()
I was able to correct it using the php that comes by default with XAMPP. I'm using windows 10 64 bits as well, but used xampp-win32-7.3.2-0-VC15 (php 7.3.2). To summarize, I was able to get a correct configuration by doing everything with 32 bits versions (except the o.s). The full story and how I've done it:
If you go to your xampp/php directory through cmd, in my case it was "C:\xampp\php", and start the php by the simple command "php" it will probably show what dlls are not being found in the etc folder or which of those are not Win 32 compatible. If you get this problem, you will not be able to see the OCI8 page when opening a phpinfo() page:
If that's the case, with win 32 compatibility problems or not finding the dlls that you are certain are there, you should unistall XAMPP and reinstall it using a x32 version. The phpinfo page will show x86 Architecture. Remember to remove in the path variables any source that miss locate your php in use, the point here is to use the one given by default in XAMPP. If you need by any reason to use another php installation, remember to use x86 architecture.
If you need an updated OCI8 dll you can download it on https://pecl.php.net/package/oci8 , but remember to check the Thread Safety compatibility, you can find it on your phpinfo page as well. In my case it was enough to use the one provided by XAMPP.
After this, you have to enable the extension:
extension=oci8_12c
in the php.ini configuration file. It was enough for me to enable only this one, although some people suggests to also enable extension=pdo_oci. My suggestion is to try this only if you failed to install with the path here shown. It's also good to check if you are set in the correct path regarding the extensions, in my case:
extension_dir="C:\xampp\php\ext"
After this, you have to download the Oracle Instant Client. Since you are using x86 architecture (you must use this one), you need to find a 32-bit version of the OIC, but is also important to check which one is compatible with the extension you uncommented. In my case, of oci8_12c, it was instantclient-basic-nt-12.2.
The final step is to unzip it to a folder, like "C:\instantclient_12_2" and add it to the path variables of the system.
Reload apache and check if the OCI8 is shown correcly.
