strstreambuf::pbackfail

virtual int pbackfail(int c = EOF);

The protected virtual member function endeavors to put back an element into the input buffer, then make it the current element (pointed to by the next pointer).

If c == EOF, the element to push back is effectively the one already in the stream before the current element. Otherwise, that element is replaced by x = (char)c. The function can put back an element in various ways:

• If a putback position is available, and the element stored there compares equal to x, it can simply decrement the next pointer for the input buffer.
• If a putback position is available, and if the strstreambuf mode says the controlled sequence is modifiable, the function can store x into the putback position and decrement the next pointer for the input buffer.

If the function cannot succeed, it returns EOF. Otherwise, if c == EOF it returns some value other than EOF. Otherwise, it returns c.