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Perform a copy on a string literal

To print the address of the object pointed to by a pointer and the address of the pointer itself, you can use %p The following code showsoriginalString andcopiedString The pointer address and the address of the pointed object:

NSString *originalString = @"Hello, World!";
NSString *copiedString = [originalString copy];

// 打印字符串内容
NSLog(@"Original: %@", originalString); // 输出: Hello, World!
NSLog(@"Copied: %@", copiedString);     // 输出: Hello, World!

// 打印指针本身的地址
NSLog(@"Original pointer address: %p", &originalString);
NSLog(@"Copied pointer address: %p", &copiedString);

// 打印指针指向对象的地址
NSLog(@"Original object address: %p", originalString);
NSLog(@"Copied object address: %p", copiedString);
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Xcode Version 15.1 (15C65) & simulator (iPhone 15) running results are as follows:

// 打印的内容一样
Original: Hello, World!
Copied: Hello, World!
// 指针本地的地址不一样，说明是不同的指针
Original pointer address: 0x7ff7b1a5fa98
Copied pointer address: 0x7ff7b1a5fa90
// 不同的指针指向同一个对象
Original object address: 0x10e4a0070
Copied object address: 0x10e4a0070
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explain

• Original: Hello, World! andCopied: Hello, World! Output string content.
• Original pointer address: %p Output pointeroriginalString Its own address on the stack.
• Copied pointer address: %p Output pointercopiedString Its own address on the stack.
• Original object address: %p OutputoriginalString The address of the string object pointed to in the heap.
• Copied object address: %p OutputcopiedString The address of the string object pointed to in the heap.

It can be seen that due to NSString is an immutable object, executingcopy method does not create a new object, but returns the same object.originalString andcopiedString They point to the same memory address (the same object address), but their pointers themselves have different addresses in the stack.

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Perform mutableCopy on string literal

    NSString *originalString = @"Hello, World!";
    NSString *copiedString = [originalString mutableCopy];

    // 打印字符串内容
    
    NSLog(@"Original: %@", originalString); // 输出: Hello, World!
    NSLog(@"Copied: %@", copiedString);     // 输出: Hello, World!

    // 打印指针本身的地址
    NSLog(@"Original pointer address: %p", &originalString);
    NSLog(@"Copied pointer address: %p", &copiedString);

    // 打印指针指向对象的地址
    NSLog(@"Original object address: %p", originalString);
    NSLog(@"Copied object address: %p", copiedString);
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Xcode Version 15.1 (15C65) & simulator (iPhone 15) running results are as follows:

Original: Hello, World!
Copied: Hello, World!
// 不同的指针
Original pointer address: 0x7ff7be102a98
Copied pointer address: 0x7ff7be102a90
// 指向不同的对象
Original object address: 0x101dfd070
Copied object address: 0x600000c80090
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