I have a bunch of strings that I need to sort. I think a std::vector would be the easiest way to do this. However, I've never used vectors before and so would like some help.
I just need to sort them alphanumerically, nothing special. Indeed, the string::compare function would work.
After that, how can I iterate through them to verify that they're sorted?
Here's what I have so far:
std::sort(data.begin(), data.end(), std::string::compare);
for(std::vector<std::string>::iterator i = data.begin(); i != data.end(); ++i)
{
printf("%s\n", i.c_str);
}
You can just do
std::sort(data.begin(), data.end());
And it will sort your strings. Then go through them checking whether they are in order
if(names.empty())
return true; // empty vector sorted correctly
for(std::vector<std::string>::iterator i=names.begin(), j=i+1;
j != names.end();
++i, ++j)
if(*i > *j)
return false;
return true; // sort verified
In particular, std::string::compare
couldn't be used as a comparator, because it doesn't do what sort
wants it to do: Return true if the first argument is less than the second, and return false otherwise. If you use sort
like above, it will just use operator<
, which will do exactly that (ie std::string
makes it return first.compare(second) < 0
).
What is the question exactly? It seems everything is already there.
However, you should probably use std::cout << *i << std::endl;
i
is an iterator == pointer to the data in the container, so *
is needed c_str()
is a function of std::string
and not a variable The problems in your code do not relate to your question?
Some hints for you:
std::vector
also overrides []
operator, so you can instead save the iterator hassle and use it like an array (iterate from 0
to vector.size()
). std::set
instead, which has automatically sorting on insertion (binary tree), so you save the extra sorting. copy(V.begin(), V.end(), ostream_iterator<std::string>(cout, "\\n"));
For sort use:
std::sort
or std::vector< std::string>::sort(..)
method.
To check if it is sorted:
use std::is_sorted
for check is sorted - http://www.sgi.com/tech/stl/is_sorted.html
or
std::adjacent_find( v.begin(), v.end(), std::greater< std::string >() ) == v.end()
for your case you could use default comparator
EDITED:
std::is_sorted
is not standard stl function, it defined in sgi stl implementation.
Thanks @Brian Neal for this note.
litb is correct, as always.
I just wanted to point out the more general point - anything that can be compared with < can be sorted with std::sort. I'll sometimes sneak an operator< member function into a struct, just so I can do this.
Sorting the string:
using namespace std; // to avoid using std everywhere
std::sort(data.begin(), data.end()); // this will sort the strings
Checking whether vector is sorted:
if(vec.empty())
return true; // empty vector is sorted correctly
for(std::vector< std::string>::iterator i=vec.begin(), j=i+1; j != vec.end(); ++i, ++j)
if(*i > *j) return false;
return true; // sort verified
C++11 Method to check sorted vector: std::is_sorted(vec.begin(),vec.end())
Now printing the sorted vector:
for(std::vector< std::string>::iterator i = vec.begin(); i != vec.end(); ++i)
{
std::cout<< *i <<std::endl;
}
Try using comaprator:
#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
//comparing function only sorts if string size is equal and keeps the larger integgers at last.
bool myfunction (string i,string j)
{
int n=i.length();
int m=j.length();
if(n==m)
return (i<j);
return n<m;
}
int main() {
int n;
cin>>n;
vector <string> arr(n);
for(int i=0;i<n;i++)
cin>>arr[i];
sort(arr.begin(),arr.end(),myfunction);
for(int i=0;i<n;i++)
cout<<arr[i]<<endl;
return 0;
}
您可以使用std::set
,它自然是一个已排序的容器。
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