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下面的示例展示了如何声明、初始化和使用原始指针。 它使用 new 初始化,以指向堆上分配的对象,必须显式删除 (delete) 该对象。 该示例还展示了与原始指针相关的一些危险。 (请记住,此示例是 C 风格的编程,而不是新式 C++!)
#include <iostream>
#include <string>
class MyClass
{
public:
int num;
std::string name;
void print() { std::cout << name << ":" << num << std::endl; }
};
// Accepts a MyClass pointer
void func_A(MyClass* mc)
{
// Modify the object that mc points to.
// All copies of the pointer will point to
// the same modified object.
mc->num = 3;
}
// Accepts a MyClass object
void func_B(MyClass mc)
{
// mc here is a regular object, not a pointer.
// Use the "." operator to access members.
// This statement modifies only the local copy of mc.
mc.num = 21;
std::cout << "Local copy of mc:";
mc.print(); // "Erika, 21"
}
int main()
{
// Use the * operator to declare a pointer type
// Use new to allocate and initialize memory
MyClass* pmc = new MyClass{ 108, "Nick" };
// Prints the memory address. Usually not what you want.
std:: cout << pmc << std::endl;
// Copy the pointed-to object by dereferencing the pointer
// to access the contents of the memory location.
// mc is a separate object, allocated here on the stack
MyClass mc = *pmc;
// Declare a pointer that points to mc using the addressof operator
MyClass* pcopy = &mc;
// Use the -> operator to access the object's public members
pmc->print(); // "Nick, 108"
// Copy the pointer. Now pmc and pmc2 point to same object!
MyClass* pmc2 = pmc;
// Use copied pointer to modify the original object
pmc2->name = "Erika";
pmc->print(); // "Erika, 108"
pmc2->print(); // "Erika, 108"
// Pass the pointer to a function.
func_A(pmc);
pmc->print(); // "Erika, 3"
pmc2->print(); // "Erika, 3"
// Dereference the pointer and pass a copy
// of the pointed-to object to a function
func_B(*pmc);
pmc->print(); // "Erika, 3" (original not modified by function)
delete(pmc); // don't forget to give memory back to operating system!
// delete(pmc2); //crash! memory location was already deleted
}
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