How to obtain data from a memory address pointed by another pointer?

Question

I am working with GenICam library, one of the methods is described as follows: enter image description here

I am using this method to get camera frames. We must provide to pBuffer a pointer, the method will return to our pointer, the memory address where data is stored.

So, I want to obtain the data stored in that memory address, but doing it in this way:

char* image_data = nullptr; 
image_data = new char[1024];
status = gentl->DSGetBufferInfo(datastream_module_handle, new_buffer_event_data.BufferHandle, GenTL::BUFFER_INFO_BASE, &info_datatype, image_data, &info_datasize);
std::cout << **image_data << std::endl;

I am getting this error: error c2100 illegal indirection c++.

I tried to use an auxiliar pointer:

char* image_data = nullptr;
image_data = new char[1024];
char* p_image_data = nullptr;
p_image_data = new char[1024];
status = gentl ... (same method)
p_image_data = *image_data;
std::cout << *p_image_data << std::endl;

but i obtained the following error: error C2440: '=' : cannot convert from char to char *.

How can I obtain the data stored in that memory address ?

There's no pointer-to-pointer in your code (nor there's any need for one). — Yksisarvinen
– Yksisarvinen, Commented Oct 3, 2018 at 8:50
You don't need new here, you can just declare char image_data[1024] (or std::array<char, 1024> image_data and pass image_data.data()) — Caleth
– Caleth, Commented Oct 3, 2018 at 9:09

Blaze · Accepted Answer · 2018-10-03 08:51:01Z

3

p_image_data = *image_data;

Should be

p_image_data = image_data;

They both have the same type (char*), so there's no need to dereference. By dereferencing image_data, you get a char again, and that can't be assigned to p_image_data (which is char*), hence the error.

Of course, now you're not copying the data, just setting the pointer. What you probably want instead is:

memcpy(p_image_data, image_data, 1024);

This copies the 1024 chars that image_data points to (after being modified by DSGetBufferInfo) to the 1024 bytes pointed to by p_image_data.

edited Oct 3, 2018 at 8:51

answered Oct 3, 2018 at 8:44

Blaze

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