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std::basic_streambuf<CharT,Traits>::setg

From cppreference.com
< cpp‎ | io‎ | basic streambuf
 
 
 
std::basic_streambuf
 
protected:
void setg( char_type* gbeg, char_type* gcurr, char_type* gend );

Sets the values of the pointers defining the get area.

After the call, eback() == gbeg, gptr() == gcurr and egptr() == gend are all true.

If any of [gbeggend), [gbeggcurr) and [gcurrgend) is not a valid range, the behavior is undefined.

[edit] Parameters

gbeg - pointer to the new beginning of the get area
gcurr - pointer to the new current character (get pointer) in the get area
gend - pointer to the new end of the get area

[edit] Example

Run this code
#include <iostream>
#include <sstream>
 
class null_filter_buf : public std::streambuf
{
 std::streambuf * src;
 char ch; // single-byte buffer
protected:
 int underflow()
 {
 traits_type::int_type i;
 while ((i = src->sbumpc()) == '0円')
 ; // skip zeroes
 if (!traits_type::eq_int_type(i, traits_type::eof()))
 {
 ch = traits_type::to_char_type(i);
 setg(&ch, &ch, &ch+1); // make one read position available
 }
 return i;
 }
public:
 null_filter_buf(std::streambuf * buf) : src(buf)
 {
 setg(&ch, &ch + 1, &ch + 1); // buffer is initially full
 }
};
 
void filtered_read(std::istream & in)
{
 std::streambuf * orig = in.rdbuf();
 null_filter_buf buf(orig);
 in.rdbuf(&buf);
 for (char c; in.get(c);)
 std::cout << c;
 in.rdbuf(orig);
}
 
int main()
{
 char a[] = "This i0円s 0円an e0円0円0円xample";
 std::istringstream in(std::string (std::begin (a), std::end (a)));
 filtered_read(in);
}

Output:

This is an example

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 4023 C++98 setg did not require the input sequence to be a valid range requires

[edit] See also

repositions the beginning, next, and end pointers of the output sequence
(protected member function) [edit]

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