"typedef struct" is not pointer?

[cerr]

Why does this little sample app not compile?
I'm using the CCS compiler version 4.119 and i'm getting the error "A
numeric expression must appear here" by the function call where i
wanna pass Foo as an argument by reference.


Code:
#include <18F87K22.h>
#device HIGH_INTS=TRUE, adc=16, ICD=TRUE

#FUSES NOWDT //No Watch Dog Timer
#FUSES WDT128 //Watch Dog Timer uses 1:128
Postscale
#FUSES HSM //Hi-Speed crystal oscillator
#FUSES NOBROWNOUT //No brownout reset
#FUSES NOPLLEN //No PLL enabled
#FUSES BBSIZ1K //1K words Boot Block size
#FUSES NOXINST //Extended set extension and Indexed
Addressing mode disabled (Legacy mode)

typedef struct {
int16 var1;
int16 var2;
int16 var3;
}MyStruct;

MyStruct TestMe;

MyFunc(MyStruct *Foo);


void main (void)
{
TestMe.var1=1;
TestMe.var2=2;
TestMe.var3=3;
MyFunc(TestMe);
}

MyFunc(MyStruct *Foo)
{
Foo->var1=Foo->var2+Foo->var3;
}

Any hints?
Thanks,
Ron

 

[Keith Thompson]

Why does this little sample app not compile?
I'm using the CCS compiler version 4.119 and i'm getting the error "A
numeric expression must appear here" by the function call where i
wanna pass Foo as an argument by reference.

I'll note that it's unlikely anyone else will be able to compile this.

Code:
#include <18F87K22.h>

Non-standard header.

#device HIGH_INTS=TRUE, adc=16, ICD=TRUE

#FUSES NOWDT //No Watch Dog Timer
#FUSES WDT128 //Watch Dog Timer uses 1:128
Postscale
#FUSES HSM //Hi-Speed crystal oscillator
#FUSES NOBROWNOUT //No brownout reset
#FUSES NOPLLEN //No PLL enabled
#FUSES BBSIZ1K //1K words Boot Block size
#FUSES NOXINST //Extended set extension and Indexed
Addressing mode disabled (Legacy mode)

These are all non-standard directives. Note also that two of your lines
were wrapped. Either limiting your line lengths or using "/* ... */"
comments would avoid this problem.

typedef struct {
int16 var1;
int16 var2;
int16 var3;
}MyStruct;

What is int16?

MyStruct TestMe;

MyFunc(MyStruct *Foo);

Suggestion: declare the return type explicitly:

int MyFunc(MyStruct *Foo);

Or, since it doesn't actually return a result:

void MyFunc(MyStruct *Foo);

Implicit int was dropped in C99, and isn't very good style even in C90.

Hmm. "//" comments were introduced in C99, the same standard that
dropped implicit int. But they're a common extension in pre-C99
compilers.

void main (void)

I presume you're using a freestanding implementation (otherwise
"int main(void)" would be the correct declaration).

{
TestMe.var1=1;
TestMe.var2=2;
TestMe.var3=3;
MyFunc(TestMe);

Myfunc expects a pointer to a MyStruct, but you're passing it
a MyStruct. I don't know why this would cause the error message
you describe.

}

MyFunc(MyStruct *Foo)
{
Foo->var1=Foo->var2+Foo->var3;

Whitespace is your friend:

Foo->var1 = Foo->var2 + Foo->var3;

is much easier to read. This looks ok *if* that int16 is a numeric
type. If not, I'd expect an error message similar to "A numeric
expression must appear here". Hmm.

}

If MyFunc() actually returns an int result, you need a return statement
here. If not, again, you should declare it returning void.

A minor style point: personally, I probably wouldn't use the typedef.
Instead, I'd write:

struct MyStruct {
/* ... */
};

and then refer to "struct MyStruct". But if you want to have a one-word
name for the type, a typedef is the way to do it.