compile error trying to call STL sort

[yinglcs]

Hi,

I have a function which calls stl sort(). I pass in a STL list of
'Rect' (my own class), like this:

void sortListY(const list<Rect>& rectList) {

sort(rectList.b egin(), rectList.end()) ; // if I comment out this
line, the program compiles fine.

}

When I try to compile it, i have these error, can you please tell me
why?
++ -O0 -g3 -Wall -c -fmessage-length=0 -osrc/RectUtils.o
.../src/RectUtils.cpp
.../src/RectUtils.cpp:6 2:2: warning: no newline at end of file
/usr/lib/gcc/i386-redhat-linux/4.0.1/../../../../include/c++/4.0.1/bits/stl_algo.h:
In function 'void std::sort(_Rand omAccessIterato r,
_RandomAccessIt erator) [with _RandomAccessIt erator =
std::_List_cons t_iterator<Rect >]':
.../src/RectUtils.cpp:4 7: instantiated from here
/usr/lib/gcc/i386-redhat-linux/4.0.1/../../../../include/c++/4.0.1/bits/stl_algo.h:2569 :
error: no match for 'operator-' in '__last - __first'
/usr/lib/gcc/i386-redhat-linux/4.0.1/../../../../include/c++/4.0.1/bits/stl_algo.h:
In function 'void std::__final_in sertion_sort(_R andomAccessIter ator,
_RandomAccessIt erator) [with _RandomAccessIt erator =
std::_List_cons t_iterator<Rect >]':
/usr/lib/gcc/i386-redhat-linux/4.0.1/../../../../include/c++/4.0.1/bits/stl_algo.h:2570 :
instantiated from 'void std::sort(_Rand omAccessIterato r,
_RandomAccessIt erator) [with _RandomAccessIt erator =
std::_List_cons t_iterator<Rect >]'
.../src/RectUtils.cpp:4 7: instantiated from here
/usr/lib/gcc/i386-redhat-linux/4.0.1/../../../../include/c++/4.0.1/bits/stl_algo.h:2213 :
error: no match for 'operator-' in '__last - __first'
/usr/lib/gcc/i386-redhat-linux/4.0.1/../../../../include/c++/4.0.1/bits/stl_algo.h:2215 :
error: no match for 'operator+' in '__first + 16'
/usr/lib/gcc/i386-redhat-linux/4.0.1/../../../../include/c++/4.0.1/bits/stl_algo.h:2216 :
error: no match for 'operator+' in '__first + 16'
/usr/lib/gcc/i386-redhat-linux/4.0.1/../../../../include/c++/4.0.1/bits/stl_algo.h:
In function 'void std::__insertio n_sort(_RandomA ccessIterator,
_RandomAccessIt erator) [with _RandomAccessIt erator =
std::_List_cons t_iterator<Rect >]':

[Victor Bazarov]

yi*****@gmail.c om wrote:

Hi,

I have a function which calls stl sort(). I pass in a STL list of
'Rect' (my own class), like this:

void sortListY(const list<Rect>& rectList) {

sort(rectList.b egin(), rectList.end()) ; // if I comment out this
line, the program compiles fine.

}

When I try to compile it, i have these error, can you please tell me
why?

Because iterators of 'std::list' are not random-access iterators. The
template 'std::list' has it own member 'sort' function. Use it.

V

[Jeff Flinn]

yi*****@gmail.c om wrote:

Hi,

I have a function which calls stl sort(). I pass in a STL list of
'Rect' (my own class), like this:

void sortListY(const list<Rect>& rectList) {

sort(rectList.b egin(), rectList.end()) ; // if I comment out this
line, the program compiles fine.

sort requires random access iterators, list provides bi-directional
iterators. Hence, list provides a sort member funtion.

Use either:

rectlist.sort() ; // req's Rect to be less than comparable

or

rectlist.sort( somepredicate );

Jeff Flinn

[yinglcs]

Thanks for all the help.

But I need to pass in a comparator, like this:

bool compare_rect_y( const Rect &r1, const Rect &r2)
{
return r1.y < r2.y;
}

void sortListY(const list<Rect>& rectList) {

rectList.sort( compare_rect_y) ;

}

I still can't get it to compile, I have this error:

g++ -O0 -g3 -Wall -c -fmessage-length=0 -osrc/RectUtils.o
.../src/RectUtils.cpp
.../src/RectUtils.cpp: In function 'void sortListY(const
std::list<Rect, std::allocator< Rect> >&)':
.../src/RectUtils.cpp:5 4: error: passing 'const std::list<Rect,
std::allocator< Rect> >' as 'this' argument of 'void
std::list<_Tp, _Alloc>::sort(_ StrictWeakOrder ing) [with
_StrictWeakOrde ring = bool (*)(const Rect&, const Rect&), _Tp = Rect,
_Alloc = std::allocator< Rect>]' discards qualifiers
make: *** [src/RectUtils.o] Error 1
make: Target `all' not remade because of errors.

Thanks for further assistance.

[Duane Hebert]

<yi*****@gmail. com> wrote in message
news:11******** **************@ g49g2000cwa.goo glegroups.com.. .

Hi,

I have a function which calls stl sort(). I pass in a STL list of
'Rect' (my own class), like this:

void sortListY(const list<Rect>& rectList) {

sort(rectList.b egin(), rectList.end()) ; // if I comment out this
line, the program compiles fine.

}

What happens if you drop the const?

[Bo Persson]

<yi*****@gmail. com> skrev i meddelandet
news:11******** *************@g 47g2000cwa.goog legroups.com...

Thanks for all the help.

But I need to pass in a comparator, like this:

bool compare_rect_y( const Rect &r1, const Rect &r2)
{
return r1.y < r2.y;
}

void sortListY(const list<Rect>& rectList) {

rectList.sort( compare_rect_y) ;

}

I still can't get it to compile,

Yes, the const is another problem. Sorting the list will update it.
..-)
Bo Persson

[Jeff Flinn]

yi*****@gmail.c om wrote:

Thanks for all the help.

But I need to pass in a comparator, like this:

bool compare_rect_y( const Rect &r1, const Rect &r2)
{
return r1.y < r2.y;
}

void sortListY(const list<Rect>& rectList) {

rectList.sort( compare_rect_y) ;
You're attempting to modify a const list, as the error message states.

Jeff

}

I still can't get it to compile, I have this error:

g++ -O0 -g3 -Wall -c -fmessage-length=0 -osrc/RectUtils.o
../src/RectUtils.cpp
../src/RectUtils.cpp: In function 'void sortListY(const
std::list<Rect, std::allocator< Rect> >&)':
../src/RectUtils.cpp:5 4: error: passing 'const std::list<Rect,
std::allocator< Rect> >' as 'this' argument of 'void
std::list<_Tp, _Alloc>::sort(_ StrictWeakOrder ing) [with
_StrictWeakOrde ring = bool (*)(const Rect&, const Rect&), _Tp = Rect,
_Alloc = std::allocator< Rect>]' discards qualifiers
make: *** [src/RectUtils.o] Error 1
make: Target `all' not remade because of errors.

Thanks for further assistance.

[yinglcs]

Thanks for all the help.