Why does Eclipse CDT say: 'syntax error', but compilation no problem

Question

I am working in existing C code which has a couple of lines with statements similar to this one:

struct collect_conn *tc = (struct collect_conn *) 
     ((char *)c - offsetof(struct collect_conn, runicast_conn));

The struct collect_conn goes along the following lines:

struct collect_conn {
  struct runicast_conn runicast_conn;
  struct announcement announcement;
  const struct collect_callbacks *cb;
  struct ctimer t;
  uint16_t rtmetric;
  uint8_t forwarding;
  uint8_t seqno;
};

I am using Eclipse CDT, and it marks the line with an orange squiggly line as 'syntax error'. I think it is marked as such by the CDT indexer. However, compilation (manually in a terminal) is no problem.

This is a bit inconvenient however, since the elements on the line don't get indexed (so the call hierarchy tree isn't always correct, or the highlighting of elements, etc.)

Why does Ecipse not like the line as it is?

Answer 1

Eclipse CDT contains its own preprocessor/parser for analyzing your code and building an index. However, when you invoke a build CDT calls out to your system compiler, like gcc for example. There may be minor differences between the syntax accepted by the CDT parser and the syntax accepted by your compiler. When this happens the CDT parser can get confused.

On my system the offsetof macro expands into an expression that uses the __offsetof__ keyword. This keyword isn't recognized by CDT so that's why there's a syntax error. To deal with this problem the CDT parser has a macro built in to deal with __offsetof__ which looks like this:

#define __offsetof__(x) (x)

This doesn't appear to be correct, at least on my system the result is the removal of the __offsetof__ keyword from the source which still leads to a syntax error.

I was able to get rid of the syntax error by going to the Paths and Symbols property page and adding a macro for __offsetof__ which maps to 'foo'. This tricks the parser into thinking its just a call to a function it hasn't seen before, but not a syntax error.

Alternatively you can turn off syntax error reporting in the editor by going to Window > Preferences > General > Editors > Text Editors > Annotations and unchecking all the checkboxes for C/C++ Indexer Markers.