Language: C

This seems like a trivial task, but I can't find an answer in the books or online.

I want to declare the const value 0x1234 in a function call, but the function takes a pointer to int.

The function: void myfunction(int*)

I want to do something like myfunction(??? 0x1234 ????);

It is similar to passing a string constant
funct(char* "some ascii text");
except I want to pass a numerical value, not ascii.

Help appreciated.

Well, don't. Instead:

The problem is that '0x1234' in this exact form is an immediate value, it has no address, and therefore it cannot be passed to a function that requires an address.

However, you could use a hack like:
You'd have to get the ascii values of whatever you wanted to pass in, and you would have to account for endianness. This is a hack and you should just declare a constant like NevemTeve says, because it is easier to implement and saner.

Thanks for replies.


The constant is actually declared in a header file for the chip eg #define StatusRegister (0x1005). There is a very large number of such constants, and I want to avoid creating an equal number of ints for that file.

I want to avoid writing a duplicate function which takes an int eg void myfunction(int)

metaschima's suggestion probably works, but I'd like something easily readable eg myfunction(???StatusRregister???)

I am certain I found the syntax to do it last year, but I have forgotten it. If there isn't a way to do it I will eat my keyboard.

IO addresses aren't memory addresses, so it would't work.
Maybe this will help: http://www.tldp.org/HOWTO/IO-Port-Programming.html#toc2

So, just creating one integer and setting it right before calling the function is not optimal ? Something like:

Really, the problem is you shouldn't declare huge tables of values using #define. Its use should be restricted to cases of substitution or a small number of values that are NOT passed around to other functions in other files. For large projects and large numbers of constants use the 'const int' instead of #define. If you had them as 'const int' there would not be a problem. Convert them all, nobody will notice.

It doesn't matter that those addresses are off-processor, the function void myfunction(int*) takes care of communicating with the chip. I can of course write code to convert the constants to ints, but I want to avoid it for reasons above and others.

I know a number of the common ways of making it work and try to avoid them for various reasons.
The header file is supplied, so it is extra work making the ints (there are a LOT of them).
Creating all those ints uses up memory, even if they are decalred const int and stored in ROM.

I am 99% sure I did it before and it worked just like myfunction("ascii text")

I make an error which might be important.

The function actually takes a pointer to char, so it is void myfunction(char*)
The declarations in the header file are char length eg #define low_voltage (0xA5)

'My apologies if I made it seem more difficult than it is.

Maybe there is a variation on the construct myfunction("ascii text"); which takes hex values eg
myfunction("?0xA5?"); which would then read like myfunction("?low_voltage?");

Why? Make it static and gcc will know to inline (assuming you compile with optimization).

Wait, are those integers actually addresses? Maybe you want
Note, this has a different meaning then the other solutions. If the others are correct then this one is wrong (and vice versa). It depends on how myfunction works.

No, they are stored on the stack, and the compiler can reuse the same spot on the stack (again, assuming optimizations enabled).

I'm afraid I was too ambiguous in my first post.
At the risk of straining helpful users, I will start a new thread which hopefully will better convey what I have in mind.
I might be mistaken in what I am trying to do, and I am making a marinade for that keyboard just in case.

The new thread that he started is here:

http://www.linuxquestions.org/questi...ar-4175513198/

The first and biggest problem is assuming that 'myfunction' expects a pointer and uses it as IO-address. It's highly unlikely it it was written by an actual programmer.