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Showing content from https://en.cppreference.com/w/cpp/language/../io/basic_streambuf/../strstreambuf/freeze.html below:

std::strstreambuf::freeze - cppreference.com

void freeze( bool freezefl = true );

(deprecated in C++98)
(removed in C++26)

If the buffer uses dynamic allocation, sets the frozen status of the stream to freezefl.

While the stream is frozen, overflow() will not reallocate the buffer and the destructor will not deallocate the buffer (thereby causing a memory leak).

[edit] Parameters freezefl - new value to set the freeze status to [edit] Return value

(none)

[edit] Notes

Every call to str() freezes the stream to preserve the validity of the pointer it returns. To allow the destructor to deallocate the buffer, freeze(false) needs to be called explicitly.

[edit] Example

In this example, initial allocation of the underlying array was for 16 bytes.

#include <iostream>
#include <strstream>
 
int main()
{
    {
        std::strstream dyn; // dynamically-allocated read/write buffer
        dyn << "Test: " << 1.23; // note: no std::ends to demonstrate append behavior
        std::cout << "dynamic buffer holds " << dyn.pcount() << " characters: '";
        std::cout.write(dyn.str(), dyn.pcount()) << "'\n";
        // the buffer is now frozen, further output will not make the buffer grow
        dyn << "more output, hopefully enough to run out of the allocated space"
            << std::ends;
        std::cout << "After more output, it holds "
                  << dyn.pcount() << " characters: '" << dyn.str() << "'\n";
        dyn.freeze(false); // unfreeze before destructor
    } // memory freed by the destructor
 
    {
        char arr[20];
        std::ostrstream st(arr, sizeof arr); // fixed-size buffer
        st << 1.23; // note: no std::ends to demonstrate append behavior
        std::cout << "static buffer holds "
                  << st.pcount() << " characters: '";
        std::cout.write(st.str(), st.pcount());
        std::cout << "'\n";
        st << "more output, hopefully enough to run out of the allocated space"
           << std::ends;
        std::cout << "static buffer holds "
                  << st.pcount() << " characters: '";
        std::cout.write(st.str(), st.pcount());
        std::cout << "'\n";
    } // nothing to deallocate, no need to unfreeze,
}

Output:

dynamic buffer holds 10 characters: 'Test: 1.23'
After more output, it holds 16 characters: 'Test: 1.23more o'
static buffer holds 4 characters: '1.23'
static buffer holds 20 characters: '1.23more output, hop'

[edit] See also disables/enables automatic reallocation
(public member function of std::strstream) [edit] disables/enables automatic reallocation
(public member function of std::ostrstream) [edit] destructs a strstreambuf object, optionally deallocating the character array
(virtual public member function) [edit] appends a character to the output sequence, may reallocate or initially allocate the buffer if dynamic and not frozen
(virtual protected member function) [edit]

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