Question

I have two files as below.

ppnfs_mutex.h

...
struct ppnfs_mutex_t
{
    pthread_mutex_t mutex;
    pthread_t owner;
    const char* context;
};
...

ppnfs_mutex.cc

#define PPNFS_MUTEX_INITIALIZER  \
    { .mutex = PTHREAD_MUTEX_INITIALIZER, .owner = 0, .context = NULL, }

struct ppnfs_mutex_t ppnfs_metadata_mutex = PPNFS_MUTEX_INITIALIZER; // line 6

I use g++ to compile this file and there is an error message as:

ppnfs_mutex.cc:6:47: error: expected primary-expression before ‘.’ token

What is the problem with the code?

Answer 1

That style of initialisation is allowed in C, but not in C++.

In C++, either initialise without naming the fields, and hope that nobody reorders them:

#define PPNFS_MUTEX_INITIALIZER {PTHREAD_MUTEX_INITIALIZER, 0, NULL}

or provide a constructor or factory function, or (if you’re using C++11) use the standard thread library rather than posix threads.