int_type overflow(int_type c = EOF);
Effects: Appends the character designated by c to the output sequence, if possible, in one of two ways:
If c != EOF and if either the output sequence has a write position available or the function makes a write position available (as described below), assigns c to *pnext++.
Returns (unsigned char)c.
If c == EOF, there is no character to append.
Returns a value other than EOF.
Returns EOF to indicate failure.
Remarks: The function can alter the number of write positions available as a result of any call.
To make a write position available, the function reallocates (or initially allocates) an array object with a sufficient number of elements n to hold the current array object (if any), plus at least one additional write position. How many additional write positions are made available is otherwise unspecified.339 If palloc is not a null pointer, the function calls (*palloc)(n) to allocate the new dynamic array object. Otherwise, it evaluates the expression new charT[n]. In either case, if the allocation fails, the function returns EOF. Otherwise, it sets allocated in strmode.
To free a previously existing dynamic array object whose first element address is p: If pfree is not a null pointer, the function calls (*pfree)(p). Otherwise, it evaluates the expression delete[]p.
If strmode & dynamic == 0, or if strmode & frozen != 0, the function cannot extend the array (reallocate it with greater length) to make a write position available.
int_type pbackfail(int_type c = EOF);
Puts back the character designated by c to the input sequence, if possible, in one of three ways:
If c != EOF, if the input sequence has a putback position available, and if (char)c == gnext[-1], assigns gnext - 1 to gnext.
Returns c.
If c != EOF, if the input sequence has a putback position available, and if strmode & constant is zero, assigns c to *--gnext.
Returns c.
If c == EOF and if the input sequence has a putback position available, assigns gnext - 1 to gnext.
Returns a value other than EOF.
Returns EOF to indicate failure.
Effects: Reads a character from the input sequence, if possible, without moving the stream position past it, as follows:
If the input sequence has a read position available, the function signals success by returning (unsigned char)*gnext.
Otherwise, if the current write next pointer pnext is not a null pointer and is greater than the current read end pointer gend, makes a read position available by assigning to gend a value greater than gnext and no greater than pnext.
Returns (unsigned char*)gnext.
Returns EOF to indicate failure.
Remarks: The function can alter the number of read positions available as a result of any call.
pos_type seekoff(off_type off, seekdir way, openmode which = in | out);
Effects: Alters the stream position within one of the controlled sequences, if possible, as indicated in Table [tab:future.seekoff.positioning].
| Conditions | Result |
| (which & ios::in) != 0 | positions the input sequence |
| (which & ios::out) != 0 | positions the output sequence |
|
(which & (ios::in | ios::out)) == (ios::in | ios::out)) and way == either ios::beg or ios::end | positions both the input and the output sequences |
| Otherwise | the positioning operation fails. |
For a sequence to be positioned, if its next pointer is a null pointer, the positioning operation fails. Otherwise, the function determines newoff as indicated in Table [tab:future.newoff.values].
| Condition | newoff Value |
| way == ios::beg | 0 |
| way == ios::cur | the next pointer minus the beginning pointer (xnext - xbeg). |
| way == ios::end | seekhigh minus the beginning pointer (seekhigh - xbeg). |
If (newoff + off) < (seeklow - xbeg) or (seekhigh - xbeg) < (newoff + off), the positioning operation fails. Otherwise, the function assigns xbeg + newoff + off to the next pointer xnext.
Returns: pos_type(newoff), constructed from the resultant offset newoff (of type off_type), that stores the resultant stream position, if possible. If the positioning operation fails, or if the constructed object cannot represent the resultant stream position, the return value is pos_type(off_type(-1)).
pos_type seekpos(pos_type sp, ios_base::openmode which
= ios_base::in | ios_base::out);
Effects: Alters the stream position within one of the controlled sequences, if possible, to correspond to the stream position stored in sp (as described below).
If (which & ios::in) != 0, positions the input sequence.
If (which & ios::out) != 0, positions the output sequence.
If the function positions neither sequence, the positioning operation fails.
For a sequence to be positioned, if its next pointer is a null pointer, the positioning operation fails. Otherwise, the function determines newoff from sp.offset():
If newoff is an invalid stream position, has a negative value, or has a value greater than (seekhigh - seeklow), the positioning operation fails
Otherwise, the function adds newoff to the beginning pointer xbeg and stores the result in the next pointer xnext.
Returns: pos_type(newoff), constructed from the resultant offset newoff (of type off_type), that stores the resultant stream position, if possible. If the positioning operation fails, or if the constructed object cannot represent the resultant stream position, the return value is pos_type(off_type(-1)).
streambuf<char>* setbuf(char* s, streamsize n);
An implementation should consider alsize in making this decision.