Question

I am trying to determine if every character in my string is alphanumeric. My compiler does not have the isalnum function.

My function is below and my_struct has a char array of size 6 (uint8 bom_pn[6]) ….and yes uint8 is a char.

boolean myfunc( my_struct * lh )
{
ret = ( isalphanum( lh->bom_pn ) && isalphanum( lh->bom_pn + 1 ) &&
        isalphanum( lh->bom_pn + 2 ) && isalphanum( lh->bom_pn + 3 ) &&
        isalphanum( lh->bom_pn + 4 ) && isalphanum( lh->bom_pn + 5 ) );
} 

My macro definition is below:

#define isalphanum(c) ( ( c >= '0' && c <= '9' ) ||  \
                        ( c >= 'A' && c <= 'Z' ) ||  \
                        ( c >= 'a' && c <= 'z' ) )

The above throws the error “operand types are incompatible (” uint8 * ” and ” int “)”

If I change my definition to the following, my code compiles and I get warnings.

#define isalphanum(c) ( ( (uint8)c >= '0' && (uint8)c <= '9' ) ||  \
                    ( (uint8)c >= 'A' && (uint8)c <= 'Z' ) ||  \
                    ( (uint8)c >= 'a' && (uint8)c <= 'z' ) )

Warning: “conversion from pointer to smaller integer”

My question is, how do I properly create this definition without warnings (and obviously check correctly).

Thanks

Answer 1

As you said lh->bom_pn is an array of bytes, which means it is effectively a pointer.

So when you pass it to isalphanum, you’re passing a pointer, and comparing it to literal bytes.

You have two options:

1.)

ret = ( isalphanum( lh->bom_pn[0] ) && isalphanum( lh->bom_pn[1] ) &&
        isalphanum( lh->bom_pn[2] ) && isalphanum( lh->bom_pn[3] ) &&
        isalphanum( lh->bom_pn[4] ) && isalphanum( lh->bom_pn[5] ) );

2.)

#define isalphanum(c) ( ( *(c) >= '0' && *(c) <= '9' ) ||  \
                        ( *(c) >= 'A' && *(c) <= 'Z' ) ||  \
                        ( *(c) >= 'a' && *(c) <= 'z' ) )

Either one should fix your problem.