在共享缓冲区内存中创建:: std :: string对象

Question

I am using Google protobuf in an embedded application with limited heap memory. I am currently trying to make the application to use dynamic allocation only as a last resort. For this, I have some shared buffer on which I create all the proto messages or most of them. Everything seems to be Ok, except for the cases where the proto message expects a ::std::string parameter.

The way I understand the ::std::string constructors description, is that it will create a copy of the data I supply. For example this constructor:

s = new(sharedBufferAddress) ::std::string(mApn, mApnSize);

where

char                        mApn[APN_MAX_SIZE];
int8_t                      mApnSize;

will create an object located at the sharedBufferAddress, but the data inside will be copied on a buffer assigned on the heap.

The question is whether there is some way to have the pointer that is returned by the c_str() function to some specified address.

Answer 1

You can not do much to hack the implementation of std::string . All attempts will do something illegal and potentially result with undefined behaviors.

One option is to evolve custom implementation of Protobuf or custom modifications of stock Protobuf.

Other option is to use existing custom implementations. For example Finnish programmer Petteri Aimonen has implemented Protobuf implementation Nanopb in C for embedded development and released it under zlib license. That can be likely more useful than custom modified stock Protobuf in your embedded project since C and C++ work passably well together.