Question for a pointer code fragment

[Linda8888]

TL;DR Summary

Assume that the function print_mem_addr(void *) takes in a pointer and prints the machine address the pointer points to as an integer value (not hexadecimal). You may use the fact that sizeof(MyType*) is 8 and sizeof(MyType) is 16. What is the value of output (A), (B) and (C)?

(I am not sure what does "(MyType **)" means after the '=' sign at the second line)

The output is :

 

[phyzguy]

It's called a 'cast'. The malloc function returns a pointer of type void*. The (MyType **) redefines the pointer to be a pointer to a pointer to a structure of type MyType. It's still a pointer (a location in memory), it's just more narrowly defined. See the link below. By the way, if you include your code in the code tags (like this above </>), then it is easy to copy and paste the code. This is better than including a picture of the code.

https://www.tutorialspoint.com/cpro...o another,as follows − (type_name) expression

 

[Linda8888]

It's called a 'cast'. The malloc function returns a pointer of type void*. The (MyType **) redefines the pointer to be a pointer to a pointer to a structure of type MyType. It's still a pointer (a location in memory), it's just more narrowly defined. See the link below. By the way, if you include your code in the code tags (like this above </>), then it is easy to copy and paste the code. This is better than including a picture of the code.

https://www.tutorialspoint.com/cprogramming/c_type_casting.htm#:~:text=Converting one datatype into another,as follows − (type_name) expression

Thanks for replying!
Why are the first output 432 and the third 1024? How do those work?

 

[Mark44]

Thanks for replying!
Why are the first output 432 and the third 1024? How do those work?

Those are the memory addresses for, respectively, arr + 3 and *arr. The code you posted first allocates enough space on the heap for 10 pointers (addresses), and then iterates 10 times to fill those 10 addresses with the addresses of chunks of heap memory.

 

[phyzguy]

Thanks for replying!
Why are the first output 432 and the third 1024? How do those work?

The operating system puts those pointers wherever it finds space available in memory. In a real system, if you ran the program multiple times, those values might be different each time. So the exact values of those pointers is not the point. Given those values, you are supposed to calculate A, B, and C.