Basically, you read a number of bytes from the file, and then unpack the values from the data read. Knowing how many bytes to read involves manual computation, as Perl doesn't know, what C compiler/struct alignment were used. If you want total overkill, there is Convert::Binary::C, which can talk to your C compiler and ask it.

It's odd that you talk of the file being defined in terms of C++ structs, since I think C++ doesn't define the memory layout of structs.

There is Convert::Binary::C, but it's usually simpler just to use unpack. You can read blocks of the appropriate size using read or by setting $/ appropriately with readline (aka <>).

(Too slow!)

Would the readline approach still work if it was a packed binary file, with fixed size records ("structs") with no end-of-record indicator?

In this case, wouldn't it be necessary to binmode the filehandle and read the required number of bytes, before unpacking?

Would the readline approach still work if it was a packed binary file, with fixed size records ("structs") with no end-of-record indicator?

I said it would. Did you got read the documentation to which I linked?

wouldn't it be necessary to binmode the filehandle

Yes, no matter which method you use.

struct mystruct {
    char a;
    int b;
    char c;
};
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I certainly would consider that approach in, for example, a module that might be deployed on different computers.   If you know that the file layout is (and will forever remain) stable, as will the source of that data file, then you might reasonably get away with using pack/unpack, which of course is designed expressly for this sort of thing.

Any such program should aggressively check for errors in the input, particularly any which imply that the unpack-information does not coincide with the data.   Realistically, only the computer itself can guard against “garbage in, garbage out stay forever” in this case.   The input program is the entire system’s first line of defense, and so it should treat every record as “Fubar until proven otherwise.”   (The “inefficiency” (sic) of doing this should be of no concern whatever.)

If you know the layout of the data types in bits, bytes, and words then it's a simple matter of unpacking the data once you've read it in.

See the unpack function and the tutorial on pack and unpack.