stl problem
Author
for some reason when i do:
list::iterator p = PlayerList.Begin();
while(p != PlayerList.End())
{
if(something)
PlayerList.Erase(p);
p++;
}
then it exits on erase. if i do erarse(p,p) then it wont erase it.
Edited by - Brad8383 on October 22, 2001 4:43:34 PM
quote:list::erase
iterator erase(iterator it);iterator erase(iterator first, iterator last);
The first member function removes the element of the controlled sequence pointed to by it. The second member function removes the elements of the controlled sequence in the range [first, last). Both return an iterator that designates the first element remaining beyond any elements removed, or end() if no such element exists.
Erasing N elements causes N destructor calls. No reallocation occurs, so iterators and references become invalid only for the erased elements.
p becomes invalid (since it''s been erased) and points to an invalid location (just like end()). Try this instead:
list::iterator p = PlayerList.begin();while(p != PlayerList.end()){ if(condition) p = PlayerList.erase(p);}
The STL sucks and it also leaks memory...I suggest not using it at all. Take the time and write your own.
quote:Original post by onlinegmz
The STL sucks and it also leaks memory...I suggest not using it at all. Take the time and write your own.
This statement is such a crock of shit that I''m convinced its author hasn''t extensively used the STL (or doesn''t know how to). The whole point of the STL is to avoid your having to write common structures and algorithms. I''m told the MSVC STL implementation is sub-par; I''ve never done the tests myself, but you can obtain alternative implementations that are much better such as STLPort.
Yup. But don't worry. Losers like that just fall behind the tech curve and wonder why they can't find a job.
PS: slight bug in your code, though it's mostly correct:
Edited by - Stoffel on October 22, 2001 5:44:25 PM
PS: slight bug in your code, though it's mostly correct:
list<POINT>::iterator p = PlayerList.begin();list<POINT>::iterator end = PlayerList.end (); // mo' efficientwhile(p != end) // end is calculated only once{ if(condition) p = PlayerList.erase(p); else ++p; // without this, it would loop forever if condition // was false} Edited by - Stoffel on October 22, 2001 5:44:25 PM
I thought erase returned the value of the next valid element, or end() if there are no more valid elements.
In any case, thanks.
In any case, thanks.
make sure to use ++p instead of p++, sometimes ++p is faster, sometimes it is the same speed, but it is never slower.
complete
i think this would work
{ Stating the obvious never helped any situation !! }
list<POINT>::iterator p = PlayerList.begin();while(p != PlayerList.end()) // end is calculated only once{ if(condition) p = PlayerList.erase(p); else ++p; } i think this would work
{ Stating the obvious never helped any situation !! }
look at the disassembly for that solution. end () is calculated each time the condition is evaluated. That was the reasoning behind my solution.
edit: Adding source code & disassembly for MSVC 6.0, in case anybody has questions.
Disassembly: first call has five instructions in loop, second has six (extra cmp).
Edited by - Stoffel on October 23, 2001 7:03:17 PM
edit: Adding source code & disassembly for MSVC 6.0, in case anybody has questions.
#include <list>#include <map>using namespace std;//typedef map<int, int> Container; // test w/ different container if you liketypedef list<int> Container;void f1 (Container &c){ // my way, added const just to be silly Container::iterator it = c.begin (); const Container::iterator end = c.end (); while (it != end) { if (rand () % 1) it = c.erase (it); else ++it; }}void f2 (Container &c){ // other way Container::iterator it = c.begin (); while (it != c.end ()) { if (rand () % 1) it = c.erase (it); else ++it; }} Disassembly: first call has five instructions in loop, second has six (extra cmp).
PUBLIC ?f1@@YAXAAV?$list@HV?$allocator@H@std@@@std@@@Z ; f1EXTRN _rand:NEAR; COMDAT ?f1@@YAXAAV?$list@HV?$allocator@H@std@@@std@@@Z_TEXT SEGMENT_c$ = 8?f1@@YAXAAV?$list@HV?$allocator@H@std@@@std@@@Z PROC NEAR ; f1, COMDAT; 11 : Container::iterator it = c.begin (); mov eax, DWORD PTR _c$[esp-4] push esi push edi mov edi, DWORD PTR [eax+4] mov esi, DWORD PTR [edi]$L10311:; 12 : const Container::iterator end = c.end ();; 13 : while (it != end) cmp esi, edi je SHORT $L9008; 14 : {; 15 : if (rand () % 1) call _rand; 16 : it = c.erase (it);; 17 : else; 18 : ++it; mov esi, DWORD PTR [esi] jmp SHORT $L10311$L9008: pop edi pop esi; 19 : }; 20 : } ret 0?f1@@YAXAAV?$list@HV?$allocator@H@std@@@std@@@Z ENDP ; f1_TEXT ENDSPUBLIC ?f2@@YAXAAV?$list@HV?$allocator@H@std@@@std@@@Z ; f2; COMDAT ?f2@@YAXAAV?$list@HV?$allocator@H@std@@@std@@@Z_TEXT SEGMENT_c$ = 8?f2@@YAXAAV?$list@HV?$allocator@H@std@@@std@@@Z PROC NEAR ; f2, COMDAT; 23 : { push esi push edi; 24 : Container::iterator it = c.begin (); mov edi, DWORD PTR _c$[esp+4] mov eax, DWORD PTR [edi+4] mov esi, DWORD PTR [eax]; 25 : while (it != c.end ()) cmp esi, eax je SHORT $L9019$L9018:; 26 : {; 27 : if (rand () % 1) call _rand; 28 : it = c.erase (it);; 29 : else; 30 : ++it; mov esi, DWORD PTR [esi] cmp esi, DWORD PTR [edi+4] jne SHORT $L9018$L9019: pop edi pop esi; 31 : }; 32 : } ret 0?f2@@YAXAAV?$list@HV?$allocator@H@std@@@std@@@Z ENDP ; f2_TEXT ENDS Edited by - Stoffel on October 23, 2001 7:03:17 PM
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