?
dieser Code:
class fdinbuf : public std::streambuf {
protected:
int fd; // file descriptor
protected:
/* data buffer:
* - at most, pbSize characters in putback area plus
* - at most, bufSize characters in ordinary read buffer
*/
static const int pbSize = 4; // size of putback area
static const int bufSize = 1024; // size of the data buffer
char buffer[bufSize+pbSize]; // data buffer
public:
/* constructor
* - initialize file descriptor
* - initialize empty data buffer
* - no putback area
* => force underflow()
*/
fdinbuf (int _fd) : fd(_fd) {
setg (buffer+pbSize, // beginning of putback area
buffer+pbSize, // read position
buffer+pbSize); // end position
}
protected:
// insert new characters into the buffer
virtual int_type underflow () {
#ifndef _MSC_VER
using std::memmove;
#endif
// is read position before end of buffer?
if (gptr() < egptr()) {
return traits_type::to_int_type(*gptr());
}
/* process size of putback area
* - use number of characters read
* - but at most size of putback area
*/
int numPutback;
numPutback = gptr() - eback();
if (numPutback > pbSize) {
numPutback = pbSize;
}
/* copy up to pbSize characters previously read into
* the putback area
*/
memmove (buffer+(pbSize-numPutback), gptr()-numPutback,
numPutback);
// read at most bufSize new characters
int num;
num = read (fd, buffer+pbSize, bufSize);
if (num <= 0) {
// ERROR or EOF
return EOF;
}
// reset buffer pointers
setg (buffer+(pbSize-numPutback), // beginning of putback area
buffer+pbSize, // read position
buffer+pbSize+num); // end of buffer
// return next character
return traits_type::to_int_type(*gptr());
}
};
Kann mir jemand erklären, was es mit dieser putback-area auf sich hat?
Wieso schreibt er nicht einfach den Buffer von vorne bis hinten voll?
Steh irgendwie auf dem Schlauch (Hab selber eine Test-Implementation gemacht, in der ich kein "putback" verwendet hab und hat so weit ich gesehen hab prima funktioniert)
