c++内存分配与释放
new/delete 与 malloc/free 区别
相同点:- 对于基本数据类型,分配和释放是一致的.
- 都不可以多次释放.
- free不改变指针的值,delete会改变.
不同点:
- malloc不会调用构造函数,free不会调用析构函数.
相同点 示例
#include <iostream>
using namespace std;
int main(int argc, char *argv[])
{
//malloc/free
int *p1 = (int*)malloc(sizeof(int));
*p1 = 888;
cout << "p1地址:" << p1 << " p1值:" << *p1 << endl;
free(p1);
cout << "free p1地址:" << p1 << " free p1值:" << *p1 << endl;
int *p2 = new int(888);
cout << "p2地址:" << p2 << " p2值:" << *p2 << endl;
delete p2; //应该在delete之后,将指针指向nullptr,不能多次delete
cout << "delete p2地址:" << p2 << " delete p1值:" << *p1 << endl;
//free之后,应该将指针指向NULL
p1 = NULL;
//delete之后,应该将指针指向nullptr
p2 = nullptr;
cin.get();
return 0;
}
不同点 示例
#include <iostream>
using namespace std;
class People
{
public:
People()
{
cout << "create people" << endl;
}
~People()
{
cout << "dispose people" << endl;
}
private:
};
//malloc/free 在c++中,使用malloc不会触发构造函数,使用free释放不会触发析构函数
int main(int argc, char *argv[])
{
cout << "执行开始" << endl;
People *p1 = (People*)malloc(sizeof(People));
free(p1);
cout << "执行结束" << endl;
cin.get();
return 0;
}
#include <iostream>
using namespace std;
class People
{
private:
char *p;
public:
People()
{
p = (char*)malloc(sizeof(char) * 1024 * 1024 * 128); //分配128兆空间
cout << "create people" << endl;
}
~People()
{
delete p; //释放空间
cout << "dispose people" << endl;
}
};
int main(int argc, char *argv[])
{
People *people(new People);
delete people; //单个对象用delete去释放
cin.get();
return 0;
}在new分配实例的时候,触发构造函数,并进行分配128兆空间
在delete释放实例之后,触发析构函数,并把在构造函数的分配的内存进行释放
delete使用注意事项
#include <iostream>
using namespace std;
class People
{
private:
char *p;
public:
People()
{
p = (char*)malloc(sizeof(char) * 1024 * 1024 * 128); //分配128兆空间
cout << "create people" << endl;
}
~People()
{
delete p; //释放空间
cout << "dispose people" << endl;
}
};
int main(int argc, char *argv[])
{
//对于基本数据类型数组,delete与delete[]作用一样
int *p = new int[10]{ 1,2,3,4,5,6,7,8,9,0 };
//delete p;
delete[] p;
//对于符合类型,单个对象用delete去释放,对象数组用delete[]去释放
People *people(new People);
delete people; //单个对象用delete去释放
//delete[]释放单个对象,会一直调用析构函数,进行释放
//delete[] people;
cin.get();
return 0;
}
秋风
2018-03-12