json - Understanding pointer casting on struct type in C -

i'm trying understanding pointer casting in case.

# https://github.com/udp/json-parser/blob/master/json.c#l408  #define json_char char typedef struct _json_object_entry {    json_char * name;    unsigned int name_length;     struct _json_value * value;  } json_object_entry; typedef struct _json_value { struct   {      unsigned int length;       json_object_entry * values;       #if defined(__cplusplus) && __cplusplus >= 201103l      decltype(values) begin () const      {  return values;      }      decltype(values) end () const      {  return values + length;      }      #endif    } object; } (*(json_char **) &top->u.object.values) += string_length + 1; 

due see top->u.object.values has address of first element of values ( type : json_object_entry ), , address of values, casting char, .. , here i'm lost. don't understand purpose of this.

// notes : 2 pass parser wonders this.

thanks

author here (guilty charged...)

in first pass, values hasn't yet been allocated, parser cheats using same field store amount of memory (length) that's going required when it's allocated in second pass.

if (state.first_pass)     (*(json_char **) &top->u.object.values) += string_length + 1; 

the cast json_char add multiples of char length, rather multiples of json_object_entry.

it bit (...ok, more bit...) of dirty hack re-using field that, save adding field json_value or using union (c89 unions can't anonymous, have made structure of json_value bit weird).

there's no ub here, because we're not using values array of structs @ point, subverting type system , using integer.