c++ - How to check alignment of returned data in the malloc() implementation? -


malloc(sz) returns memory alignment works object.

on 32-bit x86 machines, means address value returned malloc()must evenly divisible 4. in practice, 32-bit malloc implementations return 8-byte aligned memory, meaning returned addresses evenly divisible 8. should too. (on x86-64/ia-64 machines, maximum data alignment 8, malloc implementations return 16-byte aligned memory.)

i have test situation

// check alignment of returned data.   int main()   {      double* ptr = (double*) malloc(sizeof(double));      assert((uintptr_t) ptr % __alignof__(double) == 0);      assert((uintptr_t) ptr % __alignof__(unsigned long long) == 0);       char* ptr2 = (char*) malloc(1);      assert((uintptr_t) ptr2 % __alignof__(double) == 0);      assert((uintptr_t) ptr2 % __alignof__(unsigned long long) == 0);   }

my malloc code allocate more space user requested. first part of space used store metadata allocation, including allocated size.

sizeof(metadata) % 8 == 0

but heap

 static char heap[heap_capacity];

starting value not divided 8 

metadata* block = (metadata*)heap; (uintptr_t)block % 8 != 0

my tests fails, can in situation? how sure array begins address 

metadata* block = (metadata*)heap; (uintptr_t)block % 8 == 0

?

you use union force correct alignment (see union element alignment) or calculate starting index allocation correctly aligned (which reduce heap capacity 7 bytes).


Comments

Post a Comment

Popular posts from this blog

php - failed to open stream: HTTP request failed! HTTP/1.0 400 Bad Request -

this code i'm using find latitude , longitude of place: function coords($address){ echo $url="http://maps.googleapis.com/maps/api/geocode/json?address=".$address; $json = file_get_contents(urlencode($url)); $data = json_decode($json, true); print_r($data['results'][0]['geometry']['location']['lat']); print_r($data['results'][0]['geometry']['location']['lng']); } however returns warning: failed open stream: http request failed! http/1.0 400 bad request if use above code in simple procedure works fine not in function. note: have tried curl_init()... method produced same result? instead of encoding whole url encode address part. following code work fine $add='jamshoro phase 2'; $url="http://maps.googleapis.com/maps/api/geocode/json?address=".urlencode($add); $json = file_get_contents($url); $data = json_decode($json, true); print_r($data['r
Read more

java - How to filter a backspace keyboard input -

i have code gives message when key number pressed: txtvalueofclause.addeventfilter(keyevent.key_typed, new eventhandler<keyevent>() { @override public void handle(keyevent t) { char ar[] = t.getcharacter().tochararray(); char ch = ar[t.getcharacter().tochararray().length - 1]; if (!(ch >= '0' && ch <= '9')) { system.out.println("the char entered not number"); t.consume(); } } }); now if press on wrong button , press backspace remove it, error message. how can add backspace input if statement? i have found answer: txtvalueofclause.addeventfilter(keyevent.key_typed, new eventhandler<keyevent>() { @override public void handle(keyevent t) { char ar[] = t.getcharacter().tochararray(); char ch = ar[t.getcharacter().tochar
Read more

java - Show Soft Keyboard when EditText Appears -

i have code in android app, alert dialog , keyboard, , when dialog shown want keyboard appear. not , not sure why? here code: final alertdialog.builder alert = new alertdialog.builder(this); alert.settitle("title"); alert.setmessage("message"); final edittext input = new edittext(this); input.setinputtype(inputtype.type_class_number); alert.setview(input); input.setonfocuschangelistener(new view.onfocuschangelistener() { @override public void onfocuschange(view v, boolean hasfocus) { if (hasfocus) { log.i(tag, "in focus"); inputmethodmanager inputmethodmanager = (inputmethodmanager) getsystemservice(context.input_method_service); inputmethodmanager.showsoftinput(input, inputmethodmanager.show_implicit); } } }); but keyboard not appear though edit text in focus, , tell appear why, doesn't come up? thanks in advance.
Read more