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std::strstreambuf::overflow

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< cpp‎ | io‎ | strstreambuf
Revision as of 08:15, 9 September 2013 by Cubbi (Talk | contribs)

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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 allocator 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.

Contents

[edit] Parameters

c - the character to store in the put area

[edit] Return value

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

[edit] Example

#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

[edit] See also

[virtual]
writes characters to the associated output sequence from the put area
(virtual protected member function of std::basic_streambuf) [edit]
[virtual]
appends a character to the output sequence
(virtual protected member function of std::basic_stringbuf) [edit]
[virtual]
writes characters to the associated file from the put area
(virtual protected member function of std::basic_filebuf) [edit]
writes one character to the put area and advances the next pointer
(public member function of std::basic_streambuf) [edit]
inserts a character
(public member function of std::basic_ostream) [edit]