send info between apps

[Wokawidget]

Memory mapped files?

Woka

[Sam Hobbs]

Memory mapped files?

Woka

I might be using incorrect terminology but it is correct to the extent that this is a common use of the term. I don't know how familiar you are with Memory mapped files, so I should try to define them assuming you know very little. If I don't do that well enough, then say so.

Memory mapped files is a common way for processes to share data; perhaps the most common. It does seem to be an indirect solution, and it probably is, at least somewhat. A Unix system, for example, has more direct functions for sharing memory; at least if my memory is accurate.

When a file is mapped to memory, a portion of memory in each process's address space is mapped to a common portion of virtual memory. The memory can be paged in and out, but that is not done unless physical memory is used to the extent that pages need to be swapped, whether they are part of a memory-mapped file or not. Data in a memory-mapped file can be accessed as efficiently as normal memory in an address space. In terms of efficiency, the memory is the same as the rest of memory for the process. ReadProcessMemory and/or WriteProcessMemory are very inefficient in comparison.

A memory-mapped file can be backed by the pagefile(s), for which the file becomes just a way to share memory. Believe me, that is a solution that is very, very common.

[Wokawidget]

Any exmaples of code?

Woka

[Sam Hobbs]

Any exmaples of code?

Woka

How did you search? Whatever you are using to search is no good, since there should be many to be found. As soon as I get through doing things such as checking ther weather, I will look for samples using VB, and hopefully we can help you in knowing how to search.

[Wokawidget]

Hahaha. You sarcastic sod Hahaha.

OK. I will search. I was just wondering if you had any small samples to hand. Not actively looking for this code as I have no need.

Woof

[Sam Hobbs]

I did not know of any samples, expecially not VB samples. There are many more samples that use the C/C++ languages but the following are two that use VB:

Visual Basic Samples by Karl E. Peterson (MapFile.zip)
Binaryworld - Sharing Data Between Processes Using Memory-Mapped Files ... [ VB -> Memory ]

Also, the MSDN previously contained an online copy of Hardcore Visual Basic, in which there is an article called "Shared Memory Through Memory-Mapped Files".

[Wokawidget]

Cheers for that.
Just got to work. Will check out those link.

Much appreciated

Woka

[Megatron]

One of the mistakes was "subclass the receiving app"

A grave mistake, that was.

Megatron also said that it is possible to "pass the string in the lParam parameter" of a "WM_USER + X message" which is not possible. If Megatron meant that the string could be put into a lParam parameter, then it is possible to send only a few characters, not enough to be considered a string

Do you see the irony in me finger-pointing this insignificant "mistake" you made?

Life's too short to buy green bananas.

No; the WM_COPYDATA does not need custom marshalling, but WM_USER and WM_APP messages do.

No. If the data structure you're passing with WM_COPYDATA contains pointers to other locations of memory, you'll need to improvise a different approach (i.e. remove the pointers).

Receiving messages in another application that cannot be by modified at the source code level is one thing, but how to process them in that other application is a more critical problem, and likely more difficult than simply receiving the messages. Therefore I think it is best to assume that this is not a requirement until it is stated explicitly that it is.

If you're sending strings between two applications, what good is it to only be notified when a string is received? The sole reason you are sending the message (string) is so the other application can make use of it (process it). You can process the messages in that external process by subclassing. Since you have already installed a hook (the callback is already mapped into the address space of that process) you're already half-way there.

To say it's more "difficult" is subjective. Yes, there's more typing involved, but I wouldn't consider that difficult.

avoid use of ReadProcessMemory, at least in programs being developed for use by other people. I am working on getting some authoritative references on the subject.

So long as the memory locations are not modifiable by the user, it does not present a security risk. If you are not confident with your own ability to harness these functions, then don't use them.