std::strstreambuf::overflow (3) Linux Manual Page

std::strstreambuf::overflow – std::strstreambuf::overflow

Synopsis

protected:
virtual int_type overflow(int_type c = EOF);
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 <strstream>

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