How can I build a std::vector<std::string> and then sort them?

Question

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);
}

Solution 1

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 (i.e std::string makes it return first.compare(second) < 0).

Solution 2

What is the question exactly? It seems everything is already there.

However, you should probably use std::cout << *i << std::endl;

1. i is an iterator == pointer to the data in the container, so * is needed
2. 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()).
• You could use std::set instead, which has automatically sorting on insertion (binary tree), so you save the extra sorting.
• Using a functor makes your output even more fun: copy(V.begin(), V.end(), ostream_iterator<std::string>(cout, "\n"));

Solution 3

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.

Solution 4

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.

Solution 5

You could use a std::set, which is naturally a sorted container.

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