- Prev
- SystemTap Beginners Guide
- Next

### ⁠3.5.3. Incrementing Associated Values

Use `++` to increment the associated value of a unique key in an array, as in:

    array_name[index_expression] ++

Again, you can also use a handler function for your `index_expression`. For example, if you wanted to tally how many times a specific process performed a read to the virtual file system (using the event `vfs.read`), you can use the following probe:
⁠

Example 3.16. vfsreads.stp

    probe vfs.read
    {
      reads[execname()] ++
    }

In Example 3.16, “vfsreads.stp”, the first time that the probe returns the process name `gnome-terminal` (that is, the first time `gnome-terminal` performs a VFS read), that process name is set as the unique key `gnome-terminal` with an associated value of 1. The next time that the probe returns the process name `gnome-terminal`, SystemTap increments the associated value of `gnome-terminal` by 1. SystemTap performs this operation for all process names as the probe returns them.

- Prev3.5.2. Reading Values From Arrays
- Up
- Home
- Next3.5.4. Processing Multiple Elements in an Array