Use custom function and sort to sort strings by length : sort « STL Algorithms Sorting « C++ Tutorial

1. C++ Tutorial
2. STL Algorithms Sorting
3. sort

/* The following code example is taken from the book
 * "The C++ Standard Library - A Tutorial and Reference"
 * by Nicolai M. Josuttis, Addison-Wesley, 1999
 *
 * (C) Copyright Nicolai M. Josuttis 1999.
 * Permission to copy, use, modify, sell and distribute this software
 * is granted provided this copyright notice appears in all copies.
 * This software is provided "as is" without express or implied
 * warranty, and with no claim as to its suitability for any purpose.
 */

#include <iostream>
#include <vector>
#include <deque>
#include <list>
#include <set>
#include <map>
#include <string>
#include <algorithm>
#include <iterator>
#include <functional>
#include <numeric>

/* PRINT_ELEMENTS()
 * - prints optional C-string optcstr followed by
 * - all elements of the collection coll
 * - separated by spaces
 */
template <class T>
inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="")
{
    typename T::const_iterator pos;

    std::cout << optcstr;
    for (pos=coll.begin(); pos!=coll.end(); ++pos) {
        std::cout << *pos << ' ';
    }
    std::cout << std::endl;
}

/* INSERT_ELEMENTS (collection, first, last)
 * - fill values from first to last into the collection
 * - NOTE: NO half-open range
 */
template <class T>
inline void INSERT_ELEMENTS (T& coll, int first, int last)
{
    for (int i=first; i<=last; ++i) {
        coll.insert(coll.end(),i);
    }
}

using namespace std;

bool lessLength (const string& s1, const string& s2)
{
    return s1.length() < s2.length();
}

int main()
{
    vector<string> coll1;
    vector<string> coll2;

    // fill both collections with the same elements
    coll1.push_back ("1xxx");
    coll1.push_back ("2x");
    coll1.push_back ("3x");
    coll1.push_back ("4x");
    coll1.push_back ("5xx");
    coll1.push_back ("6xxxx");
    coll1.push_back ("7xx");
    coll1.push_back ("8xxx");
    coll1.push_back ("9xx");
    coll1.push_back ("10xxx");
    coll1.push_back ("11");
    coll1.push_back ("12");
    coll1.push_back ("13");
    coll1.push_back ("14xx");
    coll1.push_back ("15");
    coll1.push_back ("16");
    coll1.push_back ("17");
    coll2 = coll1;

    PRINT_ELEMENTS(coll1,"on entry:\n ");

    // sort (according to the length of the strings)
    sort (coll1.begin(), coll1.end(),           // range
          lessLength);                          // criterion
    stable_sort (coll2.begin(), coll2.end(),    // range
                 lessLength);                   // criterion

    PRINT_ELEMENTS(coll1,"\nwith sort():\n ");
    PRINT_ELEMENTS(coll2,"\nwith stable_sort():\n ");
}

on entry:
 1xxx 2x 3x 4x 5xx 6xxxx 7xx 8xxx 9xx 10xxx 11 12 13 14xx 15 16 17

with sort():
 17 2x 3x 4x 16 15 13 12 11 9xx 7xx 5xx 8xxx 14xx 1xxx 10xxx 6xxxx

with stable_sort():
 2x 3x 4x 11 12 13 15 16 17 5xx 7xx 9xx 1xxx 8xxx 14xx 6xxxx 10xxx