std::strstreambuf::overflow (3) - Linux Manuals

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

NAME

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