我可以直接将任何整数值分配给指针变量吗？

Question

由于地址是数字并且可以分配给指针变量，我可以直接将任何整数值分配给指针变量，如下所示：

int *pPtr = 60000;

Answer 1

You can, but unless you're developing for an embedded device with known memory addresses with a compiler that explicitly allows it, attempting to dereference such a pointer will invoke undefined behavior.

You should only assign the address of a variable or the result of a memory allocation function such as malloc , or NULL .

Answer 2

Yes you can. You should only assign the address of a variable or the result of a memory allocation function such as malloc, or NULL.

Answer 3

According to the pointer conversion rules, eg as described in this online c++ standard draft, any integer may be converted to a pointer value:

6.3.2.3 Pointers

(5) An integer may be converted to any pointer type. Except as previously specified, the result is implementation-defined, might not be correctly aligned, might not point to an entity of the referenced type, and might be a trap representation.

Allowing the conversion does, however, not mean that you are allowed to dereference the pointer then.

Answer 4

You can but there's a lot of considerations.

1) What does that mean ?

The only really useful abstraction when this actually gets used is that you need to access a specific memory location because something is mapped to a specific point, generally hardware control registers (less often: a specific area in flash or from the linker table). The fact that you are assigning 60000 (a decimal number rather than a hexadecimal address or a symbolic mnemonic) makes me quite worried.

2) Do you have "odd" pointers?

Some microcontrollers have pointers with strange semantics (near vs far, tied to a specific memory page, etc.) You may have to do odd things to make the pointer make sense. In addition, some pointers can do strange things depending upon where they point. For example, the PIC32 series can point to the exact same data but with different upper bits that will retrieve a cached copy or an uncached copy.

3) Is that value the correct size for the pointer?

Different architectures need different sizes. The newer data types like intptr_t are meant to paper over this.