Question

我有一个结构

#ifndef EVENT_H
#define EVENT_H
struct Event {
int ID;
int num;
int * energies;
};
#endif

和一个与Event结构一起使用的函数，

#include <fstream>
#include "Event.h"
#include <iostream>
using namespace std;
Event * read(std::ifstream& os, Event * ev)
{
if(os.fail()) return NULL;
os >> ev->ID >> ev->num;
ev->energies = new int[ev->num];
if(ev->ID!=0 && ev->num!=0){
for (int i = 0; i < ev->num; ++i)
{
os >> * (ev->energies+i);
}
}   
return ev;
}

这是main.cpp

#include <iostream>
#include <fstream>
#include "Event.h"
using namespace std;
Event * read(ifstream& os, Event * ev);
void dump(const Event& ev);
void clear(Event * ev);

int main(int argc, char const *argv[])
{
ifstream os(argv[1]);
Event * ev = new Event;
cout << "Created " << ev << endl;
Event * pointer=read(os, ev);

while(pointer!=NULL)
{
dump(*ev);
clear(ev);
Event * ev = new Event;
pointer = read(os,ev);
}
return 0;
}

我的问题是：在这种情况下，为什么在每次调用read（）函数时都没有释放内存（在read（）中用ev->energies = new int[ev->num];分配）？

Answer 1

不，内存未被释放。在函数结束时，您需要调用

delete [] ev->energies

Answer 2

您的印象是分配的指针在超出范围时将被删除。事实并非如此。它会泄漏内存。此示例将突出显示您在评论中提供的代码中缺少的内容：

#include <iostream>
using namespace std;

int* read(int *array)     {
        int i=0;
        int num=200;
        array = new int[num];
        cout << "Newly allocated pointer " << array << endl;
        if(num==0) return NULL;
        while(i<num) {
                array[i] = i*i;
                i++;
        }
        return array;
}

int main(int argc, char const *argv[])
{
  int *ptr;

  cout << "Original pointer address " << ptr << endl;
  int *n = read(ptr);
  cout << "Last value in allocated pointer " << n[199] << endl;
  cout << "Allocated pointer address " << n << endl;
  cout << "Original pointer address " << ptr << endl;
  // following line can cause a segmentation fault
  // cout << "Last value in original pointer (actually garbage) " << ptr[199] << endl;
  delete[] n; // really should delete it
}

read（）中的*数组按值传递，因此更改它将是本地范围。

关于结构上的new和delete运算符

2 个答案: