QSharedMemory and C++ objects

[faldzip]

And how did you create this 'mem' with std::vector inside?

[caduel]

QVector (and other C++ objects) contain pointers inside. These pointers are pointers inside the creating process's memory. If you put that in shared memory, the other process's accessing it will try that address - which is invalid (hopefully) for them.

You need either special containers or at least allocators to put containers into shared memory. (See e.g. Boost Interprocess)
Anything without pointers can be used (so no QString, std::string either, for example).

HTH

[MattPhillips]

Caduel,

Thanks, that was exactly it. Just to convince myself I created two structs,

struct A
{
char ch;
int i;
double d;
};
 
struct B
{
char ch;
int* i;
double d;
};

struct A
{
char ch;
int i;
double d;
};

struct B
{
char ch;
int* i;
double d;
};

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and indeed, A worked fine but B did not. Thanks again. Thanks too faldzip for your consideration.

Matt

[OverTheOCean]

Hey Matts,

did you find a way to share pointers to variables ( i.e. struct B ) ?

thanks,

Michael

[wysota]

You can't do that.

[produktdotestow]

don't exaggerate. probably there are some containers that allow you to share whole objects. just search.

[MattPhillips]

Hi,

It looks like the Boost IPC library has smart pointers which can be used within a shared memory block.

http://www.boost.org/doc/libs/1_38_0....qg_offset_ptr

But no dice with standard containers, in STL or I presume Qt as well.

Matt