Questions about typecasting

I have questions about typecasting. This is just a dummy program shown here. The actual code is too big to be posted.

typedef struct abc
{
    int a;
}abc_t;

main()
{
    abc_t *MY_str;
    char *p;
    MY_str = (abc_t *)p;
 }

Whenever I run the quality analysis check tool, I get a level 2 warning:

Casting to different object pointer type. REFERENCE - ISO:C90-6.3.4 Cast Operators - Semantics <next> Msg(3:3305) Pointer cast to stricter alignment. <next>

Can anyone please tell me how to r开发者_如何学Goesolve this issue?

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Simple - your static analysis tool (which, btw?) has decided that a char* does not have a particular alignment requirement (it could point anywhere in memory) whereas an abc_t* likely has a word alignment requirement (int must be on a 4/8 byte boundary).

In reality, as the char* is on the stack, it will be word aligned on most architectures. Your tool cannot see this.

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In your implementation (and probably many others) each int must be at an address that is divisible by sizeof int, which is often 4.

On the other hand, a char can be at any address.

It's like assigning 3.25 to an int variable. That's also not possible.

So when you have a bad pointer, you will probably get an exception from your machine, and technically this code invokes undefined behavior.

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a char* can be aligned on any byte boundary, which means if you cast it to a structure, the alignment requirements of that struct might not be met (such as 16 byte boundaries required for SIMD types).

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Your code is invalid C. If you find yourself doing something like this, it's probably the result of a greater misunderstanding. For instance I'm guessing you want to read an abc_t object from a file/socket/etc. and you're used to passing a char pointer to the read/recv/whatever function. Instead you should just declare an object of type abc_t and pass its address to whatever reading function you're using.