对字符串数组进行排序

Question

I need a quick hint on this function. So basically I have this struct, used by a class.

#include <cstring>
#include <iostream>
using namespace std;

struct postazione{
    char* nome;
    bool occupato;
};

class Aula{
    int qntpst;
    postazione * vett;
    bool full(const Aula&);
public:
    Aula(int);
    bool aggiungi(const char*);
    friend ostream& operator<<(ostream&, const Aula&);
    Aula& elimina(int);
    Aula(const Aula&); 
    Aula& operator!();
    ~Aula();
};

That is, an array of which each element is a string and a bool, but the the last one is not important now.

The ! operator has to sort the array in alphabetical order.

Here's how I tried to do it.

Aula& Aula::operator!(){
    int qnt=0;
    for(int i=0;i<qntpst;i++)
            if(vett[i].occupato)
                    qnt++;
    if(qnt!=qntpst)
            return *this;
    char *temp;
    for(int i=0;i<qntpst-1;i++){
            for(int j=i+1;j<qntpst;j++){
                    if(strcmp(vett[i].nome,vett[j].nome)>0){
                            temp=new char[strlen(vett[i].nome)+1];
                            strcpy(vett[i].nome,temp);
                            delete [] vett[i].nome;
                            vett[i].nome=new char[strlen(vett[j].nome)+1];
                            strcpy(vett[i].nome,vett[j].nome);
                            delete [] vett[j].nome;
                            vett[j].nome=new char[strlen(temp)+1];
                            strcpy(vett[j].nome,temp);
                            delete temp;
                    }
            }
    }
    return *this;
}

First 7 lines check if each bool of each element of the array is true, otherwise it won't execute. Then it starts to sort. That's how I tried to do it but it doesn't work.

PS The solution has to use an auxilary pointer, something like: aux=i; i=j; j=aux; aux=i; i=j; j=aux;

Answer 1

Quick hints.

1. Don't use operator!() to sort. Use a function named something like sort() . operator!() generally does a very different thing, and using it to sort will make your code harder to understand.
2. Don't use using namespace std in a header file (or before class definitions that rely on it). There are plenty of explanations as to why on the internet.
3. Use standard C++ library capabilities rather than rolling your own as you have.

For example, the following omits constructors and the like, but does 90% of what you seek. With no worrying about memory management, getting the algorithm to sort right, etc etc.

#include <string>
#include <vector>
#include <algorithm>

struct postazione
{
    std::string nome;
    bool occupato;
    bool operator<(const postazione & other) const
      {
           return nome < other.nome;   // std::string supports this
      };
};


class Aula
{
       std::vector<postazione> data;
   public:
      // constructors, destructors, etc

       void sort()    // sort the current vector
       {
            std::sort(data.begin(), data.end());  // this sorts using the order defined by postazione::operator<()
       }         

       Aula Sorted() const  // return a sorted copy of ourselves
       {
           Aula temp(*this);    // copy ourself
           temp.sort();         // sort the copy
           return temp;         //  return sorted copy
       };
};

The thing to realise is that std::string , std::vector (and other containers in the C++ library) keep track of their size, and resize themselves cleanly when required.

Read up on std::string and std::vector to work out what you need to do to manage them (set contents, update, etc).

Answer 2

You are not copying anything to your temporary pointer.

Change

strcpy(vett[i].nome,temp);

to

strcpy(temp, vett[i].nome);

Also, let me just say the method you're using is extremely inefficient and likely to cause problems. I would define a comparison function for your class and use std::sort(). And please, do provide more information next time, an input and an output with the expected output, it helps.