std::basic_streambuf::overflow
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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