How to get the command line from `boost::process::child` (or other classes)?

I'm using `boost::process:child` to launch a process as follows:

```c++
boost::process::child c(
boost::process::search_path("my-app"),
"--some-option",
"--verbose",
boost::process::std_out > ::stdout,
boost::process::std_in < ::stdin);
c.wait();
```

But it looks like `boost::process::child` doesn't provide any interface to return a `string` (or a `vector`) that has the actual command line. For example, in the above case, the command line may be `/usr/local/bin/my-app --some-option --verbose`.

I can surely form the `string` or `vector` by myself but I'm wondering if `boost::process` has already provided a way to get it. I searched in the documentation and examples but didn't seem to find it.

(I want to get the command line string so when an error happens I can log the actual command in the log message.)