-
Notifications
You must be signed in to change notification settings - Fork 0
/
Copy pathunique_ptr.cpp
239 lines (194 loc) · 7.1 KB
/
unique_ptr.cpp
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
#include <iostream>
#include <memory>
class MyClass
{
public:
MyClass(int val) : value(val) { std::cout << "Created MyClass with value " << value << "\n"; }
~MyClass() { std::cout << "Destroyed MyClass with value " << value << "\n"; }
void display() const { std::cout << "Value: " << value << "\n"; }
private:
int value;
};
int main()
{
std::unique_ptr<MyClass> ptr1 = std::make_unique<MyClass>(10); // Create a unique_ptr
ptr1->display();
// Transfer ownership
std::unique_ptr<MyClass> ptr2 = std::move(ptr1);
if (!ptr1)
std::cout << "ptr1 is null\n";
ptr2->display();
return 0; // ptr2 goes out of scope, and MyClass is destroyed
}
/**
Let's analyze the code with specific focus on the use of std::move and the if condition:
Key Concepts in the Code
std::move:
std::move is a utility in C++ used to indicate that the ownership of a resource should be transferred from one object to another.
In this code, it is used to transfer ownership of the std::unique_ptr object ptr1 to ptr2. After the move, ptr1 no longer owns the resource and becomes nullptr.
Why required?
std::unique_ptr enforces unique ownership. Copying a std::unique_ptr is not allowed because two unique_ptrs owning the same resource would violate the principle of sole ownership. std::move enables this transfer explicitly.
if (!ptr1) Condition:
This condition checks whether ptr1 has become null after the move operation.
ptr1 becomes null after the std::move because ownership of the managed object has been transferred to ptr2.
This if statement ensures that the program correctly identifies that ptr1 no longer owns the resource.
Code Walkthrough
Step-by-Step Execution:
Creating ptr1:
cpp
Copy code
std::unique_ptr<MyClass> ptr1 = std::make_unique<MyClass>(10);
A std::unique_ptr named ptr1 is created to manage a dynamically allocated MyClass object with value 10.
Output:
vbnet
Copy code
Created MyClass with value 10
The display method confirms the value:
makefile
Copy code
Value: 10
Transferring Ownership (std::move):
cpp
Copy code
std::unique_ptr<MyClass> ptr2 = std::move(ptr1);
Ownership of the resource is transferred from ptr1 to ptr2 using std::move.
After this line:
ptr2 now manages the MyClass object.
ptr1 is null and no longer manages any object.
Checking ptr1:
cpp
Copy code
if (!ptr1)
std::cout << "ptr1 is null\n";
The condition !ptr1 evaluates to true because ptr1 is now null after the move.
Output:
csharp
Copy code
ptr1 is null
Using ptr2:
cpp
Copy code
ptr2->display();
The display method confirms that ptr2 now owns the object:
makefile
Copy code
Value: 10
Cleanup:
When ptr2 goes out of scope at the end of main, the MyClass object is automatically destroyed by the std::unique_ptr destructor.
Output:
vbnet
Copy code
Destroyed MyClass with value 10
Full Output of the Program:
vbnet
Copy code
Created MyClass with value 10
Value: 10
ptr1 is null
Value: 10
Destroyed MyClass with value 10
Key Takeaways:
std::move:
Used to transfer ownership of resources managed by std::unique_ptr.
After std::move, the source std::unique_ptr becomes null.
if (!ptr) Check:
Ensures that the pointer no longer owns a resource, providing a safe way to confirm the state after a move.
Advantages of std::unique_ptr:
Automatic resource management (RAII).
Ensures no two std::unique_ptrs manage the same resource.
Prevents memory leaks and dangling pointers.
You said:
//E:\1ws-abhimanyu\C++Programs\cplusplus17\SmartPointer>makefile
'makefile' is not recognized as an internal or external command,
operable program or batch file.
ChatGPT said:
ChatGPT
The error occurs because you are trying to run makefile directly as a command, but makefile is not an executable file. Instead, it is a script used by the make utility to build and manage dependencies in your project.
To fix this issue, follow these steps:
1. Ensure make is Installed
The make utility is required to process a makefile. It is not natively available on Windows, but you can install it using tools like:
MinGW (Minimalist GNU for Windows): Provides a make utility.
Cygwin: A Unix-like environment for Windows that includes make.
Windows Subsystem for Linux (WSL): If you have WSL installed, it includes make
std::unique_ptr
Description: Represents sole ownership of a dynamically allocated object. No other smart pointer can share ownership of the same object.
Key Points:
When a std::unique_ptr goes out of scope, it automatically deletes the managed object.
Cannot be copied, but can be moved to transfer ownership.
Let's analyze the code with specific focus on the use of std::move and the if condition:
Key Concepts in the Code
std::move:
std::move is a utility in C++ used to indicate that the ownership of a resource should be transferred from one object to another.
In this code, it is used to transfer ownership of the std::unique_ptr object ptr1 to ptr2. After the move, ptr1 no longer owns the resource and becomes nullptr.
Why required?
std::unique_ptr enforces unique ownership. Copying a std::unique_ptr is not allowed because two unique_ptrs owning the same resource would violate the principle of sole ownership. std::move enables this transfer explicitly.
if (!ptr1) Condition:
This condition checks whether ptr1 has become null after the move operation.
ptr1 becomes null after the std::move because ownership of the managed object has been transferred to ptr2.
This if statement ensures that the program correctly identifies that ptr1 no longer owns the resource.
Code Walkthrough
Step-by-Step Execution:
Creating ptr1:
cpp
Copy code
std::unique_ptr<MyClass> ptr1 = std::make_unique<MyClass>(10);
A std::unique_ptr named ptr1 is created to manage a dynamically allocated MyClass object with value 10.
Output:
vbnet
Copy code
Created MyClass with value 10
The display method confirms the value:
makefile
Copy code
Value: 10
Transferring Ownership (std::move):
cpp
Copy code
std::unique_ptr<MyClass> ptr2 = std::move(ptr1);
Ownership of the resource is transferred from ptr1 to ptr2 using std::move.
After this line:
ptr2 now manages the MyClass object.
ptr1 is null and no longer manages any object.
Checking ptr1:
cpp
Copy code
if (!ptr1)
std::cout << "ptr1 is null\n";
The condition !ptr1 evaluates to true because ptr1 is now null after the move.
Output:
csharp
Copy code
ptr1 is null
Using ptr2:
cpp
Copy code
ptr2->display();
The display method confirms that ptr2 now owns the object:
makefile
Copy code
Value: 10
Cleanup:
When ptr2 goes out of scope at the end of main, the MyClass object is automatically destroyed by the std::unique_ptr destructor.
Output:
vbnet
Copy code
Destroyed MyClass with value 10
Full Output of the Program:
vbnet
Copy code
Created MyClass with value 10
Value: 10
ptr1 is null
Value: 10
Destroyed MyClass with value 10
Key Takeaways:
std::move:
Used to transfer ownership of resources managed by std::unique_ptr.
After std::move, the source std::unique_ptr becomes null.
if (!ptr) Check:
Ensures that the pointer no longer owns a resource, providing a safe way to confirm the state after a move.
Advantages of std::unique_ptr:
Automatic resource management (RAII).
Ensures no two std::unique_ptrs manage the same resource.
Prevents memory leaks and dangling pointers.
*/