std::strstreambuf::overflow(3)

NAME
std::strstreambuf::overflow - std::strstreambuf::overflow

Synopsis
   protected: (deprecated in C++98)
   virtual int_type overflow( int_type c = EOF ); (removed in C++26)
   Appends the character c to the put area of the buffer, reallocating if possible.
   1) If c == EOF, does nothing.
   2) Otherwise, if the put area has a write position available (pptr() < epptr()),
   stores the character as if by *pptr()++ = c.
   3) Otherwise, if the stream buffer mode is not dynamic or the stream buffer is
   currently frozen, the function fails and returns EOF.
   4) Otherwise, the function reallocates (or initially allocates) a dynamic array
   large enough to hold the contents of the current dynamic array (if any) plus at
   least one additional write position. If a pointer to the allocating function palloc
   was used in the constructor, that function is called with (*palloc)(n) where n is
   the number of bytes to allocate, otherwise new char[n] is used. If a pointer to the
   deallocating function pfree was used in the constructor, that function is called
   with (*pfree)(p) to deallocate the previous array, if needed, otherwise delete[] p
   is used. If allocation fails, the function fails and returns EOF.

Parameters
   c - the character to store in the put area

Return value
   If c == EOF, returns some value other than EOF. Otherwise, returns (unsigned
   char)(c) on success, EOF on failure.

Example
// Run this code
 #include <iostream>
 #include <strstream>
 struct mybuf : std::strstreambuf
 {
     int_type overflow(int_type c)
     {
         std::cout << "Before overflow(): size of the put area is " << epptr()-pbase()
                   << " with " << epptr()-pptr() << " write positions available\n";
         int_type rc = std::strstreambuf::overflow(c);
         std::cout << "After overflow(): size of the put area is " << epptr()-pbase()
                   << " with " << epptr()-pptr() << " write positions available\n";
         return rc;
     }
 };
 int main()
 {
     mybuf sbuf; // read-write dynamic strstreambuf
     std::iostream stream(&sbuf);
     stream << "Sufficiently long string to overflow the initial allocation, at least "
            << " on some systems.";
 }

Possible output:
 Before overflow(): size of the put area is 16 with 0 write positions available
 After overflow(): size of the put area is 32 with 15 write positions available
 Before overflow(): size of the put area is 32 with 0 write positions available
 After overflow(): size of the put area is 64 with 31 write positions available
 Before overflow(): size of the put area is 64 with 0 write positions available
 After overflow(): size of the put area is 128 with 63 write positions available

See also
   overflow writes characters to the associated output sequence from the put area
   [virtual] (virtual protected member function of std::basic_streambuf<CharT,Traits>)
   overflow appends a character to the output sequence
   [virtual] (virtual protected member function of
             std::basic_stringbuf<CharT,Traits,Allocator>)
   overflow writes characters to the associated file from the put area
   [virtual] (virtual protected member function of std::basic_filebuf<CharT,Traits>)
   sputc writes one character to the put area and advances the next pointer
             (public member function of std::basic_streambuf<CharT,Traits>)
   put inserts a character
             (public member function of std::basic_ostream<CharT,Traits>)