I am trying to sort an array of strings, but it's not sorting anything.... what am I doing wrong?
string namesS[MAX_NAMES];
int compare (const void * a, const void * b){
return ( *(char*)a - *(char*)b );
}
void sortNames(){
qsort(namesS, MAX_NAMES, sizeof(string), compare);
}
This is C++, not C. Sorting an array of strings is easy.
#include <string>
#include <vector>
#include <algorithm>
std::vector<std::string> stringarray;
std::sort(stringarray.begin(), stringarray.end());
std::sort on an array too (but std::vector is a better idea): std::sort(namesS, namesS+MAX_NAMES);
std::qsort is inherited from the standard C library. It will not work.
You need to use std::sort for sorting strings.
Specifically, cast std::string to void* and then to char* is undefined and won't work.
qsort only works with blitable (trivially copyable) types, which std::string is not.algorithm sort in CPP has the same complexity as qsort:
#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
using namespace std;
bool compare(string a, string b){
cout << "compare(" << a << "," << b << ")" << endl;
return (a.compare(b) < 0);
}
int main () {
string mystrs[] = {"www","ggg","bbb","ssss","aaa"};
vector<string> myvector (mystrs, mystrs + 5);
vector<string>::iterator it;
sort (myvector.begin(), myvector.end(), compare);
cout << "vector contains:";
for (it=myvector.begin(); it!=myvector.end(); ++it)
cout << " " << *it;
cout << endl;
return 0;
}
You can use boost::sort, like this:
#include <vector>
#include <boost/range/algorithm.hpp>
std::vector<std::string> stringarray;
boost::sort(stringarray);
If you want use find use boost::find, like this:
std::string findme;
auto offset = boost::find(stringarray, findme) - stringarray.begin()
See 2 useful functions (m_stringarray should be member of ClassA):
const size_t ClassA::GetIdByName(std::string name) const
{
return (boost::find(this->m_stringarray, name) - this->m_stringarray.begin());
}
const std::string ClassA::GetNameById(size_t id) const
{
return this->m_stringarray[id];
}
As many here have stated, you could use std::sort to sort, but what is going to happen when you, for instance, want to sort from z-a? This code may be useful
bool cmp(string a, string b)
{
if(a.compare(b) > 0)
return true;
else
return false;
}
int main()
{
string words[] = {"this", "a", "test", "is"};
int length = sizeof(words) / sizeof(string);
sort(words, words + length, cmp);
for(int i = 0; i < length; i++)
cout << words[i] << " ";
cout << endl;
// output will be: this test is a
}
If you want to reverse the order of sorting just modify the sign in the cmp function.
cmp can be just return a < b;, which is also easy to reverse. One can also avoid implementing a custom cmp and just pass either std::less<std::string>() or std::greater<std::string>() to std::sortHere is C++ another way to sort array of string without using <vector>.
#include <iostream>
#include <algorithm>
using namespace std;
int main() {
string WordArray[] = {"AA","DD","CC","BB","ZZ","NN"};
sort(begin(WordArray), end(WordArray)); /*Sort the Array*/
for(auto& Word: WordArray){
cout<<Word<<endl; /*Print Every String Element*/
}
return 0;
}
comparefunction tries to cast astringto achar *. That's definitely not a sane thing to do.