std::basic_filebuf<CharT,Traits>::underflow
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std::basic_filebuf
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basic_filebuf::underflow
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protected:
virtual int_type underflow()
virtual int_type underflow()
Reads more data into the input area.
Behaves like the base class std::basic_streambuf::underflow, except that to read the data from the associated character sequence (the file) into the get area, first reads the bytes from the file into a temporary buffer (allocated as large as necessary), then uses std::codecvt::in of the imbued locale to convert the external (typically, multibyte) representation to the internal form which is then used to populate the get area. The conversion may be skipped if the locale's std::codecvt::always_noconv returns true.
Contents
[edit] Parameters
(none)
[edit] Return value
Traits::to_int_type(*gptr()) (the first character of the pending sequence) in case of success, or Traits::eof() in case of failure.
[edit] Example
Run this code
#include <fstream> #include <iostream> struct mybuf : std::filebuf { int underflow() { std::cout << "Before underflow(): size of the get area is " << egptr()-eback() << " with " << egptr()-gptr() << " read positions available\n"; int rc = std::filebuf::underflow(); std::cout << "underflow() returns " << rc << ".\nAfter the call, " << "size of the get area is " << egptr()-eback() << " with " << egptr()-gptr() << " read positions available\n"; return rc; } }; int main() { mybuf buf; buf.open("test.txt", std::ios_base::in ); std::istream stream(&buf); while (stream.get()) ; }
Possible output:
Before underflow(): size of the get area is 0 with 0 read positions available underflow() returns 73. After the call, size of the get area is 110 with 110 read positions available Before underflow(): size of the get area is 110 with 0 read positions available underflow() returns -1. After the call, size of the get area is 0 with 0 read positions available
[edit] See also
[virtual]
(virtual protected member function of
std::basic_streambuf<CharT,Traits>) [edit]
[virtual]
(virtual protected member function of
std::basic_stringbuf<CharT,Traits,Allocator>) [edit]
[virtual]
(virtual protected member function of
std::strstreambuf) [edit]
[virtual]
(virtual protected member function) [edit]
[virtual]
(virtual protected member function) [edit]