c - using flexible array member with mmap -

i'm having trouble accessing global struct pointer i'm initalizing mmap. attempting access members of struct in functions outside of 1 declared in throw segfaults.

the struct:

typedef struct foo {   uint32_t size;   bar_t array[0]; } foo_t; 

the initialization:

foo_t* foo; // global  static void* init_function(...) {   fd = open(filename, o_creat | o_wronly, 0644);   write(...);   lseek(...);   write(...);   foo = mmap(0, big_size, prot_read | prot_write, map_shared, fd, 0);   close(fd);   foo->size = 0; } 

what causes segfault:

static int another_function(...) {   if (foo->size == 0) {...} //foo->size causes } 

big_size defined value should adequately large needs.

any ways, apologize (...)s, issues showing up. i've looked mmap docs , variable length methods no luck. in advance!

you don't show everything, seems assign global variable, don't initialize contents of mapped region. should @ least give foo->size = 0 somewhere, if file newly created, or alternatively should use ftruncate instead of fseek write sequence warrant blocks (including size) 0 filled.