CODEWITHSUNDEEP
cmacros
xsari3x
xsari3x

Reputation: 452

What's the side effect of the following macro in C ? Embedded C

#define MIN(A,B) ((A) <=  (B) ? (A) : (B))

this is the macro , I was asked what's the side effect if I used the following :

least = MIN(*p++, b);

Note: This was embedded c question

Upvotes: 5

Views: 6031

Answers (4)

Ashok
Ashok

Reputation: 11

Assume initial address of p = 0xfcf0, *p = 1, b = 2, value @ 0xfcf4 = 5 and value @ 0xfcf8 = 15

The macro will expand as

least = ((*p++) <= (b) ? (*p++) : (b));

i.e least = ((1) <= (2) ? (*p++) : (b));

since *p is incremented twice.

1) *p++ --> now p will point to address 0xfcf4;

2) *p++ --> now p will point to address 0xfcf8;

So least = 15; (the values in the address 0xfcf8). Hope it helps.

Upvotes: 1

Matteo
Matteo

Reputation: 14930

The macro will expand to:

least = ((*p++)<=(b)?(*p++):(b))

you will have then *p++ twice in your statement (i.e., it will be incremented twice).

Upvotes: 7

Gregory Pakosz
Gregory Pakosz

Reputation: 70204

*p++ gets evaluated twice as the macro expands to *p++ <= b ? *p++ : b

Also, there is no such thing as "embedded C".

Upvotes: 2

cnicutar
cnicutar

Reputation: 182649

It evaluates p++ twice. Also, since the first evaluation changes p, the second time around it will point to a different element. So the returned value will be *(initialp + 1) or b.

You should try it yourself.

Upvotes: 8

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