I have worked constantly in single quotes, that I have completely forgotten the use of double quotes.
Today I had styles in a file, among others like this:
echo '#parent';
and I had to migrate to
echo "#parent";
And now how can I operate the reserved php variables in double quotes
$row = "www";
echo "base64_encode($row)";
In single quotes I did it in the following way:
$row = "www";
echo ''.base64_encode($row).'';
It can be done practically, doing the same, the difference is that double quote is added:
$row = "www.example.com";
echo "".base64_encode($row)."";
You can see the demo
Deputy source on varied use of double and single quote.
On the basis of what you are trying to do:
<?php
$row = "www";
echo ''.base64_encode($row).'';
The direct equivalent with double quotes would be:
<?php
$row = "www";
echo "".base64_encode($row)."";
An empty string of single quotes, '' , can also be represented with double quotes, "" .
Even so the correct way (without unnecessarily concatenating empty strings) to do so would be:
<?php
$row = "www";
echo base64_encode($row);
This is because in your code with single quotes you are concatenating an empty string before and after the call to base64_encode() , being completely unnecessary to do so since echo can directly receive the output of base64_encode() without need to do nothing more.
Regarding the attempt you have made:
<?php
$row = "www";
echo "base64_encode($row)";
It is not possible to execute a function (or method) inside the double quotes. In the PHP documentation you can see that you can only interpret values of variables or properties of class.