共享指针解除引用错误

Question

Java guy here trying to get my head around C++, specifically shared pointers . I'm using the Point Cloud Library to do some surface work. The PCL library contains IndicesPtr which according to the documentation is a shared pointer on a std::vector .

How do I access the vector from the pointer? I have tried dereferencing with

pcl::IndicesPtr sample(new std::vector<int>());
...
for (int i = 0; i < *sample.size(); i++) { ... }

as per the documentation here https://theboostcpplibraries.com/boost.smartpointers-shared-ownership . Compiling then gives me the error

error: no member named 'size' in 'boost::shared_ptr<std::__1::vector<int, std::__1::allocator<int> > >'; did you mean to use '->' instead of '.'?
    for (int i = 0; i < *sample.size(); i++) {

What am I doing wrong here?

Answer 1

It should either be (*sample).size() because operator . has higher precedence over dereference operator * or just sample->size() .

Answer 2

According to operator precedence , operator. has higher precedence than operator* . So *sample.size() is same as *(sample.size()) . That's why the compiler tried to tell you that you can't invoke size() on a boost::shared_ptr directly.

You can add parentheses to specify precedence explicitly, eg (*sample).size() ; or as the compiler suggested, change it to sample->size() .