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

Sometimes, although the code compiles with no error, eclipse CDT's real-time code analyzer shows some errors in C/C++ files (eg. 'Function xxx could not be resolved). This is because eclipse CDT uses its own preprocessor/parser for analyzing the code and building the indexes instead of the MinGW's one (or any other GNU compiler). In order to fix this globally for all eclipse projects in the workspace, follow these steps: (In order to fix this only for a specific project, follow steps 1, 2 and 4 in menu 'Project->Preferences')

1-In menu 'Window->Preferences->C/C++->Language Mappings', add the correct mappings as shown in below: (eg. for content types: C++ Source/Header File, use GNU C++ language and so on)

2-In menu 'Window->Preferences->C/C++->Indexer', set full indexing by checking all checkboxes (but not 'Skip' ones) as shown in below:

3-In each project's specific properties, menu 'Project->Properties->C/C++ general->Indexer', Uncheck 'Enable project specific settings' as shown in below:

4-Rebuild the indexing, menu 'Project->C/C++ Index->Rebuild'.

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.

I've fixed problem in eclipse CDT with Preferences->C/C++->Language Mappings : Add Content Type : C-header Language : C++

It seems the CDT parser doesn't like the portion offsetof(struct ...). If you declare collect_conn using a typedef the error goes away. At least for me, the following code works:

typedef struct  {
   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;
} collect_conn;
...
struct collect_conn *tc = (struct collect_conn *)
     ((char *)c - offsetof(collect_conn, runicast_conn));

If you can't change the original declaration do something like this:

typedef struct collect_conn collect_conn_t;