list <string> lstStrings;
lstStrings.push_back("BBBBBB");
lstStrings.push_back("AAAAAA");
lstStrings.push_back("CCCCCC");
lstStrings.sort();
How do you sort a list of strings ???
Author
I have a list of strings that I want to sort:
How do I sort the list of strings ascending and descending?
The list's sort() member function can take a sorting criterion as a parameter. i.e. the function to use to determine whether A < B.
Example:
Note that VC6's implementation is flawed and will not accept this code. I can't remember the workaround right now, sorry.
Example:
#include <list>#include <functional>using namespace std;list<string> lstStrings;lstStrings.push_back("BBBBBB");lstStrings.push_back("AAAAAA");lstStrings.push_back("CCCCCC");// descending orderlstStrings.sort( greater<string>() );Note that VC6's implementation is flawed and will not accept this code. I can't remember the workaround right now, sorry.
A link that might be useful to you is this link.
A lot of algorithms are already provided in STL and a lot of people seem not to use them, while they should :)
Hope this helps
Eric
A lot of algorithms are already provided in STL and a lot of people seem not to use them, while they should :)
Hope this helps
Eric
Quote:Original post by utilae
whats ascending?
IS it:
less<string>()
Yes, that's the default comparison criterion. For a given comparison criterion f and two objects A and B, then A comes before B in the sorted output if f(A,B) is true. It's easy to see that less leads to an ascending order (assuming that operator<() has been implemented properly for the type being considered).
By the way, when sorting you can also give your own predicate, something like this :
// Tests for something.. like the lenght of the string
bool MyTestPredicate(const std::string& in_lhs, const std::string& in_rhs)
{
return in_lhs.size() < in_rhs.size();
}
std::sort(mylist.begin, mylist.end, MyTestPredicate);
(I haven't compiled anything, but I guess this should work...)
This way, if you're storing structs that you'd like to be sorted in different ways, like based on different members or something, you can have a few predicates and select the one appropriate to your operation.
Hope this helps
Eric
// Tests for something.. like the lenght of the string
bool MyTestPredicate(const std::string& in_lhs, const std::string& in_rhs)
{
return in_lhs.size() < in_rhs.size();
}
std::sort(mylist.begin, mylist.end, MyTestPredicate);
(I haven't compiled anything, but I guess this should work...)
This way, if you're storing structs that you'd like to be sorted in different ways, like based on different members or something, you can have a few predicates and select the one appropriate to your operation.
Hope this helps
Eric
Quote:Original post by xEricx
std::sort(mylist.begin, mylist.end, MyTestPredicate);
(I haven't compiled anything, but I guess this should work...)
You should really avoid using std::sort with a std::list. Even if it works (which isn't guaranteed), the lack of random access will kill performance. That's why std::list has its own sort() member function.
With that caveat, I agree with your observation. It's just that the standard library already does provide the basic functors.
... and if you were using boost::lambda, you could even write mylist.sort(_1<_2); for ascending order and mylist.sort(_2<_1); for descending order.
Quote:Original post by FrunyQuote:Original post by xEricx
std::sort(mylist.begin, mylist.end, MyTestPredicate);
(I haven't compiled anything, but I guess this should work...)
You should really avoid using std::sort with a std::list. Even if it works (which isn't guaranteed), the lack of random access will kill performance. That's why std::list has its own sort() member function.
Couldn't/why don't they do tag dispatching in std::sort to fix this? Right now if you have a typedef for some container type, and you switch to/from a list, you may need to fix sort calls as well :s I can understand not providing an operator[], but list sorting (via mergesort or whatever) is within the same order of complexity as general-case sorting with random access being available :/
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