Order of operations for dereference and bracket-ref in C

Question

If I do *ptr[x], is that equivalent to *(ptr[x]), or (*ptr)[x]?

Solution 1

*(ptr[x])

See the Wikipedia operator precedence table, or, for a more detailed table, this C/C++ specific table.

Solution 2

In C, all postfix operators have higher precedence than prefix operators, and prefix operators have higher precedence than infix operators. So its *(ptr[x])

Comments

[Claudiu]

that link doesn't mention pointer dereferencing... but it does say array access binds most tightly

[Justin Ardini]

The * is in the 2nd row of the table, after [] in the 1st row.

[Justin Ardini]

Ah, I see how this could be confusing, since * could mean multiplication or pointer dereference. Multiplication goes after though, in row 3 of the table.

[Claudiu]

ah yes, reading comprehension for the win. i was scanning the text for mention of the word 'pointer' and didn't realize it's just a unary operation too.

[Claudiu]

where does this counterclockwise method come from?

[Matthew Flaschen]

Wikipedia also has a comprehensive C(++)-specific precedence table.

[t0mm13b]

@Claudiu: It's a well known technique for parsing and analyzing C expressions...it is found in 'Expert C Programming - Peter Van der Linden', see stackoverflow.com/questions/2305255/…

[Steve Jessop]

That's for parsing type specifiers and declarations. But in the question *ptr[x] is an expression, and so all you need to know is operator precedence.

[Justin Ardini]

@Matthew: Thanks, incorporated this table into my post.

[Nick T]

So the counter-clockwise thing doesn't apply to expressions? I would strongly drop mentioning that, as operator precedence is all that matters here.

[Nick T]

Yay, my favorite table. ( en.wikipedia.org/wiki/… )