[c++] shared_ptr with malloc and free


To use a std::shared_pointer with malloc() and free() you should specify a custom deleter. This should do it

std::shared_ptr<T> ptr(static_cast<T*>(malloc(sizeof(T))), free);

As long as you do not pass around the result of std::shared_ptr<T>::get(), your pointer is safe.

Edit: Added casting the result of malloc() to T*.


I have working in large application which contain c and cpp. The all files saved as cpp extension but the code is written in c- style. I mean it is define structure rather than class allocate memory through malloc and realloc and calloc.In recent They have installed boost library So I am planning to use into my existing code base So I have some following question.

  1. Can I use std::shared_ptr with malloc and free.
  2. If yes, can anyone point out me sample code base?
  3. Will it impact any functionality if I create std::shared_ptr in my application and pass this pointer to another function, which uses malloc or calloc?

Or in other words:

How do I achieve the similar functionality with std::shared_ptr, for the following code:

void allocateBlocks(int **ptr, int *cnt)
    *ptr = (int*)malloc(sizeof(int) * 10);
    *cnt = 10;
    /*do something*/ 

int main()
    int *p = NULL;
    int count = 0;
    allocateBlocks(&p, &count);
    /*do something*/


We call some functions, which accept double pointer and fill the structure inside their application and use malloc. Can we assign those pointer to std::shared_ptr? For example:

typedef struct txn_s
    int s;
    int d;
    int *e;
} txn_t;

typedef boost::shared_ptr<txn_t> tpointer;