stl_util.h

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// Protocol Buffers - Google's data interchange format
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// https://developers.google.com/protocol-buffers/
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// from google3/util/gtl/stl_util.h
 
#ifndef GOOGLE_PROTOBUF_STUBS_STL_UTIL_H__
#define GOOGLE_PROTOBUF_STUBS_STL_UTIL_H__
 
#include <google/protobuf/stubs/common.h>
 
namespace google {
namespace protobuf {
 
// STLDeleteContainerPointers()
//  For a range within a container of pointers, calls delete
//  (non-array version) on these pointers.
// NOTE: for these three functions, we could just implement a DeleteObject
// functor and then call for_each() on the range and functor, but this
// requires us to pull in all of algorithm.h, which seems expensive.
// For hash_[multi]set, it is important that this deletes behind the iterator
// because the hash_set may call the hash function on the iterator when it is
// advanced, which could result in the hash function trying to deference a
// stale pointer.
template <class ForwardIterator>
void STLDeleteContainerPointers(ForwardIterator begin,
                                ForwardIterator end) {
  while (begin != end) {
    ForwardIterator temp = begin;
    ++begin;
    delete *temp;
  }
}
 
// Inside Google, this function implements a horrible, disgusting hack in which
// we reach into the string's private implementation and resize it without
// initializing the new bytes.  In some cases doing this can significantly
// improve performance.  However, since it's totally non-portable it has no
// place in open source code.  Feel free to fill this function in with your
// own disgusting hack if you want the perf boost.
inline void STLStringResizeUninitialized(string* s, size_t new_size) {
  s->resize(new_size);
}
 
// Return a mutable char* pointing to a string's internal buffer,
// which may not be null-terminated. Writing through this pointer will
// modify the string.
//
// string_as_array(&str)[i] is valid for 0 <= i < str.size() until the
// next call to a string method that invalidates iterators.
//
// As of 2006-04, there is no standard-blessed way of getting a
// mutable reference to a string's internal buffer. However, issue 530
// (http://www.open-std.org/JTC1/SC22/WG21/docs/lwg-active.html#530)
// proposes this as the method. According to Matt Austern, this should
// already work on all current implementations.
inline char* string_as_array(string* str) {
  // DO NOT USE const_cast<char*>(str->data())! See the unittest for why.
  return str->empty() ? nullptr : &*str->begin();
}
 
// STLDeleteElements() deletes all the elements in an STL container and clears
// the container.  This function is suitable for use with a vector, set,
// hash_set, or any other STL container which defines sensible begin(), end(),
// and clear() methods.
//
// If container is nullptr, this function is a no-op.
//
// As an alternative to calling STLDeleteElements() directly, consider
// ElementDeleter (defined below), which ensures that your container's elements
// are deleted when the ElementDeleter goes out of scope.
template <class T>
void STLDeleteElements(T *container) {
  if (!container) return;
  STLDeleteContainerPointers(container->begin(), container->end());
  container->clear();
}
 
// Given an STL container consisting of (key, value) pairs, STLDeleteValues
// deletes all the "value" components and clears the container.  Does nothing
// in the case it's given a null pointer.
 
template <class T>
void STLDeleteValues(T *v) {
  if (!v) return;
  for (typename T::iterator i = v->begin(); i != v->end(); ++i) {
    delete i->second;
  }
  v->clear();
}
 
}  // namespace protobuf
}  // namespace google
 
#endif  // GOOGLE_PROTOBUF_STUBS_STL_UTIL_H__