What do these printf statements in the functions print?

Question

BlackTom AI · Accepted Answer

This question asks what the two printf statements will print given the function and main setup.
First, observe the function FUNC: it takes a parameter p of type int *, then reassigns p to point to memory allocated by malloc(100). This reassignment affects only the local parameter variable p inside FUNC; it does not modify the actual pointer passed from the caller.
Next, in main, there is int *ptr; which is an uninitialized pointer. The call FUNC(ptr) passes ptr by value, so FUNC changes only its local copy (p); ptr in main remains unchanged after the call.
Inside FUNC, the statement p = (int *)malloc(100); makes p hold the address of a newly allocated block. Then printf("p:%x", p); prints the value of p, i.e., the address of that allocated block, in hexadecimal.
Back in main, after FUNC returns, we execute printf("ptr:%x", ptr); which prints the value of ptr. Since ptr was never initialized or assigned a real address in main (the assignment happened only to the local parameter p inside FUNC), ptr still contains an indeterminate value, which leads to undefined behavior when printed.
Now evaluating the options one by one:
- Option 1: "both printf statements print the contents of the same (identical) integer array" is incorrect because there is no integer array being printed, and the two statements do not print the same content; one prints the allocated pointer address, the other prints an indeterminate value from an uninitialized pointer.
- Option 2: "printf statements print the same (identical) pointer values" is incorrect; the addresses come from two different pointers: p inside FUNC points to malloc’d memory, while ptr in main remains uninitialized.
- Option 3: "printf statements print different pointer values, as one is an integer pointer but the other is an unitialized int pointer" is the most accurate: both are int pointers, but the first prints the address of the allocated memory stored in p, and the second prints whatever indeterminate value ptr holds in main because it was never assigned.
- Option 4: "the printf statements print the contents of different integer arrays" is incorrect because there is no array being printed, and the statements print pointer addresses, not array contents.
In summary, the key idea is understanding that the assignment to p inside FUNC does not affect ptr in main, so the two printf outputs will display different pointer values due to one being a valid allocated address and the other being an uninitialized pointer value, which is undefined behavior when printed.

What do these printf statements in the functions print?单项选择题

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