Annex D (normative) Compatibility features [depr]

D.6 char* streams [depr.str.strstreams]

D.6.1 Class strstreambuf [depr.strstreambuf]

D.6.1.3 strstreambuf overridden virtual functions [depr.strstreambuf.virtuals]

int_type overflow(int_type c = EOF) override;
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.
332 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) override;
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.
Remarks: If the function can succeed in more than one of these ways, it is unspecified which way is chosen.
The function can alter the number of putback positions available as a result of any call.
int_type underflow() override;
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) override;
Effects: Alters the stream position within one of the controlled sequences, if possible, as indicated in Table 145.
Table 145seekoff 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 146.
Table 146newoff 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) override;
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) override;
Effects: Implementation defined, except that setbuf(0, 0) has no effect.
An implementation should consider alsize in making this decision.