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    <p>what make me confuse is, why you need to allocate or create an object in SharedMemory (SHM), for example if you reserve shared memory of the size 65536 Bytes, then suppose you get your shared memory at address <code>0x1ABC0000</code>, if reservation success you will have free and directly accessible memory space at <code>0x1ABC0000 to 0x1ABCFFFF</code>.</p> <p>then when your application need to "allocate" object in SHM of size <code>sizeof(SHMObject)</code>, and your memory manager see that address at <code>0x1ABC0000+0x1A</code> is free, your memory manager should just return <code>0x1ABC001A</code> value, and mark <code>( 0x1ABC001A to 0x1ABC001A+sizeof(SHMObject) )</code> was occupied, and you just need to cast: <code>SHMObject* shmObjectPtr = (SHMObject*)(0x1ABC001A);</code></p> <p>and ofcourse that is assuming you have your own custom memory allocator that work on specified range of memory address.</p> <p>as for template, i don't really understand how does your SHM ring buffer look like, but I've done that before using SHM, my implementation is like this: `</p> <pre><code>//memory SHM allocator template&lt;typename T&gt; class ShmRingAllocator { protected: void* baseAddress; public: ShmRingAllocator(void* baseAddress,int memSize); void* allocate(); //this function do what I described earlier, or you can use placement new: new (baseAddress+offset)T; } //some kind of shared_ptr&lt;&gt; that handle object in SHM, this provides mechanishm to check is the pointer still valid in shm or not template&lt;typname T&gt; ShmRingObjectPtr { protected: T* object; //mapped address of object at current process ShmBuffer* shm; //every object has pointer to which SHM does this pointer pointing at public: virtual T* operator-&gt;(); //operator overload to access T object } class ShmBuffer //base class for all kind of SHM buffer { protected: std::string shmName; void* shmBasePtr; } template&lt;typename T,class A=ShmRingAllocator&lt;T&gt;&gt; ShmRingBuffer : public ShmBuffer { protected: A allocator; public: ShmRingObjectPtr&lt;T&gt; insert() //push one element to ring buffer { return ShmRingObjectPtr&lt;T&gt;((T*)this-&gt;allocator.allocate(),this); } } </code></pre> <p>`</p>
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    1. POAdding an allocator to a C++ class template for shared memory object creation
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    1. COYour SHM buffer prototype is very useful, thanks! I sort of understand the way you implemented it using custom SHM allocators. What I cannot understand is how you access your ShmBuf from different processes, a writer and a reader. Say, I create the ShmBuf in the writer and insert elements into it. How does an independen reader process access that object and read data from it (you also don't seem to have a pop() member).
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    2. COif you want different process to be able to write and read,I solve it by creating offset_ptr<> this is again just like shared_ptr<> but contain 64-bit pointer address (on x86 platform), first it contain shm base address, and second contain offset from the base address, by using this you can use or write a pointer inside shmBUffer that pointing to data on shmBUffer, thus all pointer inside shm will point to same data in that shmBuffer, because its using offset from their own base address in each process. and the rest is just about sync, since you have virtually exact memory space between proces
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