c++ - What means the error : ..."bytes to alignment boundary" in Xcode/Clang? -

transformnode 4 bytes alignment boundary

and here code cause warning :

class transformnode : public node { public:     int number;  public:      void test() { number = 12; } };  //node.h class node { public:     typedef std::set<node *> childset;  protected:     childset mchildren;     node * mparent;  public:     node(node * parent=0) : mparent(parent) {}     ~node() {}      node * addchild(node * node);     inline node * getparent() { return mparent; }      const childset &getchildren() const { return mchildren; } };   inline void node_test() {     transformnode * node = new transformnode;     node->test();     std::cout << node->number << "\n"; }  int main() {      node_test();     return 0; } 

the error happens when derive node class class transformnode. using xcode 5.0 warnings turned on , treating warnings errors. want understand going on code, turning off warnings or stop treating them errors not way want handle this.

edit: added more code. clarification on details (in bold)

thanks,
gasim

i'm not sure if you're seeing error. generally, "all warnings" includes kinds of stuff barely considered warnings; heck, part aren't super informative either.

alignment issue don't care unless you're working specific hardware in embedded system. happening compiler defaults 8-byte alignment, , when define transformnode class, allocating 4 bytes int , "wasting" 4 more bytes align entire class 8-byte boundary. compiler warning telling "wasted" 4 bytes. said, not care this.

i think in general you'll drive mad if have maximal warnings , warnings-as-errors turned on. more useful step 1 level of warning , treat error if want super-clean.

reedit: clarified answer in light of recent edits.

another thought: try adding int in transformnode class , see if warning goes away (i'm assuming because int #2 "use up" "wasted" 4 bytes).

you can check out http://en.wikipedia.org/wiki/data_padding understand issue better.