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Showing content from https://en.cppreference.com/w/cpp/string/basic_string/../../io/strstreambuf/~strstreambuf.html below:

std::strstreambuf::~strstreambuf - cppreference.com

virtual ~strstreambuf();

Destroys a std::strstreambuf object. if the object is managing a dynamically-allocated buffer (the buffer state is "allocated") and if the object is not frozen, then deallocates the buffer using the deallocation function provided at construction or delete[] if none was provided.

(none)

This destructor is typically called by the destructor of std::strstream.

If str() was called on a dynamic strstream and freeze(false) was not called after that, this destructor leaks memory.

#include <iostream>
#include <strstream>
 
void* my_alloc(size_t n)
{
    std::cout << "my_alloc(" << n << ") called\n";
    return new char[n];
}
 
void my_free(void* p)
{
    std::cout << "my_free() called\n";
    delete[] (char*)p;
}
 
int main()
{
    {
        std::strstreambuf buf(my_alloc, my_free);
        std::ostream s(&buf);
        s << 1.23 << std::ends;
        std::cout << buf.str() << '\n';
        buf.freeze(false);
    } // destructor called here, buffer deallocated
 
    {
        std::strstreambuf buf(my_alloc, my_free);
        std::ostream s(&buf);
        s << 1.23 << std::ends;
        std::cout << buf.str() << '\n';
//      buf.freeze(false);
    } // destructor called here, memory leak!
}

Output:

my_alloc(4096) called
1.23
my_free() called
my_alloc(4096) called
1.23

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