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std::vector resizes when the code does philosophers.emplace_back(), which can move the elements in memory, so that their previous addresses become invalid and the feed() function ends up accessing objects using their old invalid addresses.

A fix would be to make the philosopher class non-copyable and non-movable, and then use std::list or std::forward_list instead of std::vector. std::list and std::forward_list do not move elements in memory and hence are capable of storing non-copyable and non-moveable objects.

You may also like to use std::thread instead of pthread_t, and std::mutex instead of pthread_mutex_t. The std classes are non-copyable/movable which would prevent you from making this error at compile-time. Also, the code doesn't check return values of the pthread functions for errors, whereas std::thread and std::mutex do that for you.

Working with UNC resources is contrary to the nature of cross-browser web platform such as Dynamics 365. Along with the kludgy experience for Windows users, which apparently isn't working anyway, consider the experience for Mac and mobile users when they try to open a UNC path in their browser.

SharePoint would be the obvious choice, but with that off the table, you might want to look into implementing WebDAV on the server that's hosting the files.

These days I doubt that many would consider WebDAV to be a "modern" or popular solution for D365 file integration.

Outside of SharePoint, Azure Blob storage is a viable and popular cloud-based option.

What you have overloaded is the pre-increment operator.
What you are using is the post-increment operator.

You can either use the pre-increment operator:

• Avoid mutable state like the plague.

  One of the main points of using functional programming, possibly the main one, is to avoid all the little pitfalls, bugs, issues one needs to deal with when using mutable state. You should do everything you can in order to avoid mutating state. For instance, instead of using C-style for-loops where you need to keep a counter variable updated, use map and other higher-order functions in order to abstract away your iteration patterns. This also means that you should never change the value of a variable if you can avoid that. Instead, you should be defining almost all of your variables, preferrably all of them, as constants, and using functions to compute new values from them instead of mutating them.

• Avoid side-effects like the plague.

  Mutable state's ugly cousin, side-effects. Side effects mean anything other than taking a value and returning a value in a function. If that function prints data, mutates global variables, sends messages to threads, or anything, anything other than simply taking its parameters, computing a value from them, and returning a value, that function has side-effects. Side-effects are important (see next bullet point), but if you use them a lot, they get impossible to track. Just think of how everyone tells you to avoid global variables in imperative programming. Functional programming goes a step further and tries to avoid all side-effects. The bulk of your program should be made of pure functions. (See ahead)

• When you need to use side-effects, keep them contained.

  Yes, I just told you to run away from side-effects. However, no program is useful without side-effects of some kind. Graphical User Interface? Side-effect. Audio output? Side-effect. Printing to a shell? Side-effect. So you can't really get rid of side-effects if you want to build useful stuff. What you should do instead is write your code so that all your side-effecting code lives in a thin layer which mostly calls pure functions and then does the required side-effects using the result of these pure function calls.

• Use pure functions for everything you can.

  This is sort of the flipside of the previous point. A pure function is a function which has no side-effects and does not mutate anything. It can only take in parameters and return a value. You should use these a lot. For instance, instead of doing your logging within functions which are computing stuff, you should be constructing your log strings using pure functions, and then letting your side-effects layer call these pure functions, call more pure functions in order to format the log strings into a full log, and then output the log itself from your side-effects layer.

• Use higher-order functions to structure your code.

  Higher-order functions are, in a way, the glue that makes functional programming work. A higher-order function is a function which takes one or more functions as parameters and/or returns a function. The power of higher-order functions is that they can encapsulate many of the patterns which you would use in an imperative-style program in a declarative manner. For instance, let's take a look at the three most common higher-order functions:

  map is a function which takes a function and a list of values, applies its function argument to each of those values, and returns a new list with the results. map encapsulates the whole pattern of iterating over a list doing an operation on each value in a declarative manner.

  filter is a function which takes a function which returns a boolean and a list of values, applies its function argument to each of those values and returns a list containing only those values for which its function argument returns true. It encapsulates the whole pattern of selecting results from a list in a declarative manner.

  reduce, also known as fold, takes an initial value, a binary function and a list of values. It uses its function argument to combine the initial value with the first value of the list, then combines the result with the next value of the list and keeps on doing this until it has reduced the list to just one single value. It encapsulates the entire pattern of obtaining an aggregate value from a list of values.

  This is in no way an exhaustive list of higher-order functions, but these three are the most common ones. I hope this has been enough to show how you can structure code which would require a lot of tracking variables using only functions in a declarative manner. If you use these higher-order functions well, it's likely you won't ever need a for or while loop again.

This is definitely not an exhaustive list of functional programming practices, but I think most functional programmers would agree these five guidelines form the core of what functional programming is about. If you want to really learn how to apply these, my advice would be to learn a pure functional programming language such as Haskell, so you are forced to abandon the imperative paradigm and to learn how to structure things functionally instead. I would recommend the fantastic Haskell Programming from First Principles as a starting resource if you choose to go this way. In case you don't want to/can't put down the cash, Brent Yorgey's Haskell course at UPenn is also a great free resource.