std::basic_stringbuf<CharT,Traits,Allocator>::overflow

Appends the character c to the output character sequence.

# Declarations

protected:
virtual int_type overflow( int_type c = Traits::eof() );

# Parameters

c: the character to store in the put area

# Return value

Traits::eof() to indicate failure, c if the character c was successfully appended, or some value other than Traits::eof() if called with Traits::eof() as the argument.

# Notes

This function is different from a typical overflow() which moves the contents of the buffer to the associated character sequence because for a std::basic_stringbuf, the buffer and the associated sequence are one and the same.

# Example

#include <sstream>
#include <iostream>
 
struct mybuf : std::stringbuf
{
    mybuf(const std::string& new_str,
          std::ios_base::openmode which = std::ios_base::in | std::ios_base::out)
        : std::stringbuf(new_str, which) {}
 
    int_type overflow(int_type c = EOF) override
    {
        std::cout << "stringbuf::overflow('" << char(c) << "') called\n"
                  << "Before: size of get area: " << egptr() - eback() << '\n'
                  << "        size of put area: " << epptr() - pbase() << '\n';
 
        int_type ret = std::stringbuf::overflow(c);
 
        std::cout << "After : size of get area: " << egptr() - eback() << '\n'
                  << "        size of put area: " << epptr() - pbase() << '\n';
 
        return ret;
    }
};
 
int main()
{
    std::cout << "read-write stream:\n";
    mybuf sbuf("   "); // read-write stream
    std::iostream stream(&sbuf);
    stream << 1234;
    std::cout << sbuf.str() << '\n';
 
    std::cout << "\nread-only stream:\n";
    mybuf ro_buf("   ", std::ios_base::in); // read-only stream
    std::iostream ro_stream(&ro_buf);
    ro_stream << 1234;
 
    std::cout << "\nwrite-only stream:\n";
    mybuf wr_buf("   ", std::ios_base::out); // write-only stream
    std::iostream wr_stream(&wr_buf);
    wr_stream << 1234;
}

# Defect reports

DR	Applied to	Behavior as published	Correct behavior
LWG 169	C++98	the buffer (re)allocated could only hold one extra character	allows more extra characters
LWG 432	C++98	overflow moved epptr() to point just past the newwrite position if the std::stringbuf is open for input	it is not moved