Question

I’m constructing a struct with one of the member being a map.
First question is this allowed? The compiler did not complain.

struct A {  
  map<int, float> B;  
}  

Later I declare an array of such data type.

A *C = (A *)INTERNAL_CALLOC(..., sizeof(A));  

Here the function INTERNAL_CALLOC is a functional wrapper of MALLOC.
Later on in the code when I try to first time insert an item into the array’s first element’s map, I got a core dump.

C[0].B[0] = 0.001;  

Any idea why is this the case?
Thanks!

Answer 1

Yes, a map in a struct is fine.

Allocating with malloc is definitely not fine; the constructor is not called. So your map will most likely do something terrible when you attempt to use it.

General rule of thumb: don’t use malloc/calloc/realloc/free in C++. Avoid dynamic allocation wherever possible, and use new/delete when unavoidable.^*

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_{* And read up on smart pointers.}