std::basic_streambuf::overflow

性病：基本[医]流光：：溢出

virtual int_type overflow( int_type ch = Traits::eof()

确保在放置面积保存一些字符的初始子序列，从pbase()到输出序列并更新指向PUT区域%28的指针(如果需要的话)为%29。如果ch不是Traits::eof()%28i.e.Traits::eq_int_type(ch, Traits::eof()) != true%29，它要么放到PUT区域，要么直接保存到输出序列中。

该功能可能更新pptr，，，epptr和pbase用于定义写入更多数据的位置的指针。如果失败，该函数将确保pptr() == nullptr或pptr() == epptr...

函数的基类版本什么也不做。派生类可以重写此函数，以便在耗尽时允许更新PUT区域。

参数

ch	-	the character to store in the put area

返回值

返回不等于Traits::eof()在成功的时候，Traits::eof()在失败的时候。

函数的基类版本返回Traits::eof()...

注

大sputc()和sputn()在溢出%28的情况下调用此函数pptr() == nullptr或pptr() >= epptr()29%。

例

二次

#include <iostream>
#include <array>
 
// Buffer for std::ostream implemented by std::array
template<std::size_t SIZE, class CharT = char>
class ArrayedStreamBuffer : public std::basic_streambuf<CharT> {
public:
 
    using Base = std::basic_streambuf<CharT>;
    using char_type = typename Base::char_type;
    using int_type = typename Base::int_type;
 
    ArrayedStreamBuffer() : buffer_{} // value-initialize buffer_ to all zeroes
    {
        Base::setp(buffer_.begin(), buffer_.end() // set std::basic_streambuf
            // put area pointers to work with 'buffer_'
    }
 
    int_type overflow(int_type ch) 
    {
        std::cout << "overflow\n";
        return Base::overflow(ch
    }
 
    void print_buffer()
    {
        for (const auto& i: buffer_) {
            if (i == 0) {
                std::cout << "NULL";
            } else {
                std::cout << i;
            }
            std::cout << " ";
        }
        std::cout << "\n";
    }
 
private:
    std::array<char_type, SIZE> buffer_;
};
 
int main()
{
    ArrayedStreamBuffer<10> streambuf;
    std::ostream stream(&streambuf
 
    stream << "hello";
    streambuf.print_buffer(
    if (stream.good()) {
        std::cout << "stream is good\n";
    }
 
    stream << "world";
    streambuf.print_buffer(
    if (stream.good()) {
        std::cout << "stream is good\n";
    }
 
    stream << "!";
    streambuf.print_buffer(
    if (!stream.good()) {
        std::cout << "stream is not good\n";
    }
}

二次

产出：

二次

h e l l o NULL NULL NULL NULL NULL 
stream is good
h e l l o w o r l d 
stream is good
overflow
h e l l o w o r l d 
stream is not good

二次

另见

uflow virtual	reads characters from the associated input sequence to the get area and advances the next pointer (virtual protected member function)
underflow virtual	reads characters from the associated input sequence to the get area (virtual protected member function)
overflow virtual	writes characters to the associated file from the put area (virtual protected member function of std::basic_filebuf)
overflow virtual	appends a character to the output sequence (virtual protected member function of std::basic_stringbuf)
overflow virtual	appends a character to the output sequence, may reallocate or initially allocate the buffer if dynamic and not frozen (virtual protected member function of std::strstreambuf)

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