Question

I can see this has been asked countless times but I couldn't quite relate the answers I found my individual situation. I'm still getting the hang of C and haven't quite got my head around pointers yet. A basic version of the code I'm having issue with is below:

int function(unsigned long *timestamp)
{
     timestamp = GetTick();
}

Where the GetTick() function returns a value of type uint32_t.

My problem then is that I get a compiler warning that the assignment makes a pointer from an integer without a cast. I understand that pointers and variables are different but I don't fully understand what the meaning of the warning is nor the right way to make the assignment? Any suggestions?

Edit: Might be worth mentioning that I didn't write this code myself, I'm simply trying to port it to use a new set of drivers that should allow it to do the same thing, in theory.

Update:

A cleaner version of the above code:

int function(unsigned long *timestamp)
{
     if (timestamp)
         timestamp = GetTick();
     return 0;
}

Answer 1

My problem then is that I get a compiler warning that the assignment makes a pointer to an integer

No, the warning is saying the opposite: you're making an integer into a pointer. That's because GetTick returns an integer but you're assigning the result to timestamp, which is a pointer. You probably meant:

    *timestamp = GetTick();

Answer 2

You need to use:

*timestamp = GetTick();

as you have passed pointer and you need to set the value at the memory address pointed to by the pointer.

Answer 3

timestamp is a pointer, GetTick() returns a value. You should do

int function(unsigned long *timestamp)
{
     *timestamp = GetTick();
}

Answer 4

a pointer is just an address unsigned long *timestamp= NULL. To get the underlying value stored at that address you must de-reference the pointer *timestamp. since you are passing in a pointer to the function if you want to assign a value you must use, in this case, *timestamp = GetTick();

In addition, if(timestamp) will be checking the pointer address. if you want it to check if there is an existing value within the pointer you again need to de-reference, if(*timestamp)

Assignment makes pointer from integer without a cast warning

4 个答案: