The standard template library supports sorting of a vector. You need to include <algorithm>. Then, to sort v, just call sort(v.begin(), v.end()). Below I have two programs that are nearly identical. One of them (src/sortlines1.cpp) sorts lines of standard input. The other (src/sortints.cpp) sorts standard input when it is read in as integers.
/* This program sorts the lines of standard input
using the sort() procedure from
the STL algorithms library. */
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
int main()
{
vector <string> lines;
string s;
size_t i;
/* Read lines of standard input into the vector "lines".
Sort the vector using the sort() procedure,
and print the sorted lines. */
while (getline(cin, s)) lines.push_back(s);
sort(lines.begin(), lines.end());
for (i = 0; i < lines.size(); i++) {
cout << lines[i] << endl;
}
return 0;
}
|
/* This program sorts integers read on standard
input, using the sort() procedure from the
STL algorithms library. */
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
int main()
{
vector <int> numbers;
int n;
size_t i;
/* Read integers into the vector "numbers".
Sort the vector using the sort() procedure,
and print the sorted numbers. */
while (cin >> n) numbers.push_back(n);
sort(numbers.begin(), numbers.end());
for (i = 0; i < numbers.size(); i++) {
cout << numbers[i] << endl;
}
return 0;
}
|
By default, strings are sorted lexicographically and numbers numerically (duh):
UNIX> cat files/input-names.txt Sydney Ingratiate Arianna Exonerate Sarah Charcoal Alexis Kaitlyn Inferential Cole Hunter Ourselves Joseph Dilatory Julian Fluvial Mia Leah Skied Oliver Celebrate Liam Trisyllable UNIX> bin/sortlines1 < files/input-names.txt Alexis Kaitlyn Inferential Arianna Exonerate Cole Hunter Ourselves Joseph Dilatory Julian Fluvial Liam Trisyllable Mia Leah Skied Oliver Celebrate Sarah Charcoal Sydney Ingratiate UNIX> | UNIX> cat files/input-numbers-1.txt 87 76 24 4 34 27 93 11 58 54 UNIX> bin/sortints < files/input-numbers-1.txt 4 11 24 27 34 54 58 76 87 93 UNIX> |
You'll note that if we sort that numerical file as strings, it will put "4" between "34" and "54":
UNIX> bin/sortlines1 < files/input-numbers-1.txt 11 24 27 34 4 54 58 76 87 93 UNIX> |
And remember that sortlines1.cpp reads strings, complete with their spaces, while sortints.cpp reads numbers:
UNIX> cat files/input-numbers-2.txt 87 76 24 4 34 27 93 11 58 54 UNIX> bin/sortlines1 < files/input-numbers-2.txt 87 76 24 11 58 54 4 34 27 93 UNIX> | UNIX> bin/sortints < files/input-numbers-2.txt 4 11 24 27 34 54 58 76 87 93 UNIX> |
If you want to sort, but you don't want to use the default sorting mechanism, you can provide your own comparison function. It should take two parameters of the same type as the vector (preferably const and reference) and return a bool (true or false). It should return true if the first parameter is less than the second, and false otherwise. Therefore, the following program (src/sortlines2.cpp) sorts standard input by the value of the second character in each line:
/* This program uses a comparison function to sort a vector of strings by the
strings' second letters, rather than the entire strings. */
#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
using namespace std;
/* Your comparison function takes as arguments, two const references to
the type that is in the vector (strings). */
bool string_compare(const string &s1, const string &s2)
{
if (s1[1] < s2[1]) return true; /* I could have just said "return (s1[1] < s2[1]);" */
return false;
}
int main()
{
vector <string> lines;
string s;
size_t i;
/* This code is the same as before, except we pass string_compare() to the sort() procedure. */
while (getline(cin, s)) lines.push_back(s);
sort(lines.begin(), lines.end(), string_compare);
for (i = 0; i < lines.size(); i++) cout << lines[i] << endl;
return 0;
}
|
I've highlighted the second characters in blue so that you can see that they are indeed sorted:
UNIX> bin/sortlines2 < files/input.txt Sarah Charcoal Liam Trisyllable Mia Leah Skied Oliver Celebrate Alexis Kaitlyn Inferential Joseph Dilatory Cole Hunter Ourselves Arianna Exonerate Julian Fluvial Sydney Ingratiate UNIX>