Wrong result on second call bb_compare()

By Dmitry , 7 November, 2024
Forums
Gurux.DLMS

Hi, Mikko!

I try compare two buffers twice.

unsigned char vnd[] = "VND";
gxData vndr; // here byteArr "VND"

unsigned char c = bb_compare(vndr.value.byteArr, vnd, 3); //OK, c==1
c = bb_compare(vndr.value.byteArr, vnd, 3); //Fail, c == 0

This is because if the buffers are equal, position of vndr.byteArr changes to length of comparing.

How to compare buffers multiple times?

Thanks!

Kurumi

1 year 10 months ago

Hi,

If compare succeeds, the bb_compare increases the byte array position with the length of compared str;

Try this:

unsigned char c = bb_compare(vndr.value.byteArr, vnd, 3); //OK, c==1
if (c)
{
vndr.value.byteArr-position -= 3;
}
c = bb_compare(vndr.value.byteArr, vnd, 3);

BR,
Mikko

Dmitry

1 year 10 months ago

Thanks for you reply.

It's work.

But i think comparing should not change internal state of buffers.

Also i try this:
if(vndr.value.vt == DLMS_DATA_TYPE_OCTET_STRING)
{
bool res = (memcmp(vndr.value.byteArr->data, vnd, sizeof(vnd)-1) == 0);
}