Delete all items from a c std vector

Question

I m trying to delete everything from a std  vector by using the following code  vector erase  vector begin    vector end        but it doesn t work     Update  Doesn t clear destruct the elements held by the vector  I don t want that  as I m still using the objects  I just want to empty the container

User · Answer

Adding to the above mentioned benefits of swap    That clear   does not guarantee deallocation of memory   You can use swap   as follows   std  vector lt T gt    swap myvector

User · Answer

vector clear   should work for you  In case you want to shrink the capacity of the vector along with clear then   std  vector lt T gt  v  swap v

User · Answer

If your vector look like this std  vector lt MyClass  gt  vecType pt you have to explicitly release memory  Or if your vector look like   std  vector lt MyClass gt  vecType obj   constructor will be called by vector Please execute example given below   and understand the difference       class MyClass           public          MyClass                         cout lt  lt  MyClass  lt  lt endl                     MyClass                         cout lt  lt   MyClass  lt  lt endl                       int main                  typedef std  vector lt MyClass  gt  vecType ptr          typedef std  vector lt MyClass gt  vecType obj          vecType ptr myVec ptr          vecType obj myVec obj          MyClass obj          for int i 0 i lt 5 i                          MyClass  ptr new MyClass                myVec ptr push back ptr               myVec obj push back obj                     cout lt  lt   n n---------------------If pointer stored---------------------  lt  lt endl          myVec ptr erase  myVec ptr begin   myVec ptr end             cout lt  lt   n n---------------------If object stored---------------------  lt  lt endl          myVec obj erase  myVec obj begin   myVec obj end             return 0

User · Answer

If you keep pointers in container and don t want to bother with manually destroying of them  then use boost shared ptr  Here is sample for std  vector  but you can use it for any other STL container  set  map  queue         include  lt iostream gt   include  lt vector gt   include  lt boost shared ptr hpp gt   struct foo       foo  const int i x     d x  i x                 std  cout  lt  lt   foo  foo    lt  lt  d x  lt  lt  std  endl              foo                 std  cout  lt  lt   foo   foo    lt  lt  d x  lt  lt  std  endl             int d x      typedef boost  shared ptr lt  foo  gt  smart foo t   int main         std  vector lt  smart foo t  gt  foos      for   int i   0  i  lt  10    i                 smart foo t f  new foo  i              foos push back  f               foos clear         return 0

User · Answer

Use v clear   to empty the vector   If your vector contains pointers  clear calls the destructor for the object but does not delete the memory referenced by the pointer   vector lt SomeClass  gt  v 0    v push back  new SomeClass  one       v clear       Memory leak where  one  instance of SomeClass is lost

User · Answer

Is v clear   not working for some reason

User · Answer

I think you should use std  vector  clear   vec clear        EDIT      Doesn t clear destruct the elements   held by the vector    Yes it does  It calls the destructor of every element in the vector before returning the memory  That depends on what  elements  you are storing in the vector  In the following example  I am storing the objects them selves inside the vector   class myclass   public       myclass                        std  vector lt myclass gt  myvector      myvector clear       calling clear will do the following     1  invoke the deconstrutor for every myclass    2  size    0  the vector contained the actual objects     If you want to share objects between different containers for example  you could store pointers to them  In this case  when clear is called  only pointers memory is released  the actual objects are not touched   std  vector lt myclass  gt  myvector      myvector clear       calling clear will do     1  ---------------    2  size    0  the vector contained  pointers  not the actual objects     For the question in the comment  I think getVector   is defined like this   std  vector lt myclass gt  getVector      Maybe you want to return a reference      vector getVector   clear   clears m vector in this case std  vector lt myclass gt  amp  getVector

User · Answer

class Class  std  vector lt Class  gt  vec   some data   for  unsigned int i vec size    i gt 0         --i      delete vec i       vec pop back         Free memory  efficient for large sized vector vec shrink to fit      Performance  theta n   If pure objects  not recommended for large data types  then just     vec clear

User · Answer

vector clear   is effectively the same as vector erase  vector begin    vector end       If your problem is about calling delete for each pointer contained in your vector  try this    include  lt algorithm gt   template lt  typename T  gt  struct delete pointer element       void operator    T element   const               delete element                   std  for each  vector begin    vector end    delete pointer element lt int  gt         Edit  Code rendered obsolete by C  11 range-for

[c++] Delete all items from a c++ std::vector

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