Debuggin a Simple STL Algorithm :: STL
Author
Hi.
I would like to debug a simple algorithm that does not work using an STL solution. The solution works via iteration.
std::list theList;
for (unsigned int i = 0; i < 10; ++i)
theList.push_back(i);
// theList should now contain 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9.
// Remove "6" from the list.
// Assume that iTheList is an iterator that points to element with value 6.
theList.erase(iTheList);
// After erase() theList should now contain 0, 1, 2, 3, 4, 5, 7, 8, and 9.
Okay. Everything above works as designed. Now I would like to decrement everything bigger or equal to "6," thus make theList hold 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. Here is the iterative solution.
-----
// Given iTheList points to theList.begin().
while (*iTheList <= 6)
++iTheList
// Now decrement until end of theList.
while (*iTheList != theList.end()
{
*iTheList = *iTheList - 1;
++iTheList;
}
-----
The iterative solution above works perfect.
I would like to implement a more efficient and elegant solution. Here is one solution using STL algorithms. However, it does not work correctly.
-----
std::for_each(std::find_if(theList.begin(), theList.end(), std::bind2nd(std::greater<>, 6)), theList.end(), std::bind2nd(std::minus<>, 1));
-----
The STL solution above does not work. The logic and syntec seem to be valid.
Is there a logic or syntec misunderstanding in the STL solution? I looked over the function objects and function adapter. They are valid.
Thanks,
KUphryn
for_each never assigns the result of the operation back, it just calls the function.
You are just doing value - 1, not value = value - 1.
That's the job of transform.
itor = theList.erase( std::find( theList.begin(), theList.end(), 6 ) );
std::transform( itor, theList.end(), itor, std::bind2nd( std::minus<int>(), 1 ) );
Documents [ GDNet | MSDN | STL | OpenGL | Formats | RTFM | Asking Smart Questions ]
C++ Stuff [ MinGW | Loki | SDL | Boost. | STLport | FLTK | ACCU Recommended Books ]
[edited by - Fruny on October 25, 2002 4:01:04 AM]
You are just doing value - 1, not value = value - 1.
That's the job of transform.
itor = theList.erase( std::find( theList.begin(), theList.end(), 6 ) );
std::transform( itor, theList.end(), itor, std::bind2nd( std::minus<int>(), 1 ) );
Documents [ GDNet | MSDN | STL | OpenGL | Formats | RTFM | Asking Smart Questions ]
C++ Stuff [ MinGW | Loki | SDL | Boost. | STLport | FLTK | ACCU Recommended Books ]
[edited by - Fruny on October 25, 2002 4:01:04 AM]
Author
Okay. I added a class object that will do the minus manually.
Here the call to it.
The compiler will not compile. Here is the errors.
I defined DecreaseOne functor as a global class.
What is the problem?
Thanks,
Kuphryn
[edited by - kuphryn on October 25, 2002 12:27:44 PM]
template <typename T>class DecreaseOne : public std::binary_function<T, T, void>{ public: void operator()(T &lp, const T &rp) { lp -= rp; }}; Here the call to it.
std::for_each(std::find_if(theList.begin(), theList.end(), std::bind2nd(std::greater<size_t>(), 6)), theList.end(), std::bind2nd(DecreaseOne<size_t>(), 1)); The compiler will not compile. Here is the errors.
error C2064: term does not evaluate to a functionerror C2662: 'DecreaseOne<unsigned int>::operator`()'' : cannot convert 'this' pointer from 'const DecreaseOne<T>' to 'DecreaseOne<T> &' with [ T=size_t ] and [ T=size_t ] I defined DecreaseOne functor as a global class.
What is the problem?
Thanks,
Kuphryn
[edited by - kuphryn on October 25, 2002 12:27:44 PM]
This topic is closed to new replies.
Advertisement
Popular Topics
Advertisement
