time_t **now = NULL

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time_t **now = NULL;

The code you provided declares a pointer named `now` that has a type of `time_t **`. Let's break down what this means:

1. `time_t` is a data type in C and C++ that represents time and dates. It's often used to store and manipulate timestamps.

2. `time_t *` is a pointer to a `time_t`. In other words, it can store the memory address of a `time_t` variable.

3. `time_t **` is a pointer to a pointer to a `time_t`. This means it can store the memory address of a pointer to a `time_t` variable.

In this line of code, `now` is being declared as a pointer to a pointer to a `time_t`, and it's initialized to `NULL`, meaning it currently doesn't point to any valid memory location. 

Here are a few possible use cases for such a declaration:

1. Dynamic Memory Allocation: You might use `time_t **` when you want to allocate memory for a 2D array of `time_t` values dynamically. You can allocate memory for rows of `time_t *` and then allocate memory for each row separately.

2. Function Parameters: If you pass `time_t **now` as a parameter to a function, the function can modify the pointer `now` to point to a different location or update the value pointed to by `now`.

3. Building Data Structures: You might use this type when you're building complex data structures that involve multiple levels of indirection.

In summary, `time_t **now` declares a pointer to a pointer to a `time_t`, and its usage would depend on the specific context of your code, but it's often used for managing multi-dimensional arrays or passing pointers to functions that need to modify the pointer itself or the data it points to.