int_type sputbackc( char_type c ); |
Puts back a character back to the get area.
If a putback position is available in the get area (gptr() > eback()), and the character c is equal to the character one position to the left of gptr() (as determined by Traits::eq(c, gptr()[-1]), then simply decrements the next pointer (gptr()).
Otherwise, calls pbackfail(Traits::to_int_type(c)) to either back up the get area or to modify both the get area and possibly the associated character sequence.
The I/O stream function basic_istream::putback is implemented in terms of this function.
| c | - | character to put back |
If putback position was available, returns the character that the next pointer is now pointing at, converted to int_type with Traits::to_int_type(*gptr()). The next single-character input from this streambuf will return this character.
If putback position was not available, returns what pbackfail() returns, which is Traits::eof() on failure.
#include <iostream>
#include <sstream>
int main()
{
std::stringstream s("abcdef"); // gptr() points to 'a' in "abcdef"
std::cout << "Before putback, string holds " << s.str() << '\n';
char c1 = s.get(); // c1 = 'a', gptr() now points to 'b' in "abcdef"
char c2 = s.rdbuf()->sputbackc('z'); // same as s.putback('z')
// gptr() now points to 'z' in "zbcdef"
std::cout << "After putback, string holds " << s.str() << '\n';
char c3 = s.get(); // c3 = 'z', gptr() now points to 'b' in "zbcdef"
char c4 = s.get(); // c4 = 'b', gptr() now points to 'c' in "zbcdef"
std::cout << c1 << c2 << c3 << c4 << '\n';
s.rdbuf()->sputbackc('b'); // gptr() now points to 'b' in "zbcdef"
s.rdbuf()->sputbackc('z'); // gptr() now points to 'z' in "zbcdef"
int eof = s.rdbuf()->sputbackc('x'); // nothing to unget: pbackfail() fails
if (eof == EOF)
std::cout << "No room to putback after 'z'\n";
}Output:
Before putback, string holds abcdef After putback, string holds zbcdef azzb No room to putback after 'z'
| moves the next pointer in the input sequence back by one (public member function) |
|
| puts character into input stream (public member function of std::basic_istream) |
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