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// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_SCOPED_BSTR_WIN_H_
#define BASE_SCOPED_BSTR_WIN_H_
#include <windows.h>
#include <oleauto.h>
#include "base/logging.h"
// Manages a BSTR string pointer.
// The class interface is based on scoped_ptr.
class ScopedBstr {
public:
ScopedBstr() : bstr_(NULL) {
}
// Constructor to create a new BSTR.
// NOTE: Do not pass a BSTR to this constructor expecting ownership to
// be transferred - even though it compiles! ;-)
explicit ScopedBstr(const wchar_t* non_bstr);
~ScopedBstr();
// Give ScopedBstr ownership over an already allocated BSTR or NULL.
// If you need to allocate a new BSTR instance, use |allocate| instead.
void Reset(BSTR bstr = NULL);
// Releases ownership of the BSTR to the caller.
BSTR Release();
// Creates a new BSTR from a wide string.
// If you already have a BSTR and want to transfer ownership to the
// ScopedBstr instance, call |reset| instead.
// Returns a pointer to the new BSTR, or NULL if allocation failed.
BSTR Allocate(const wchar_t* wide_str);
// Allocates a new BSTR with the specified number of bytes.
// Returns a pointer to the new BSTR, or NULL if allocation failed.
BSTR AllocateBytes(int bytes);
// Sets the allocated length field of the already-allocated BSTR to be
// |bytes|. This is useful when the BSTR was preallocated with e.g.
// SysAllocStringLen or SysAllocStringByteLen (call |AllocateBytes|) and
// then not all the bytes are being used.
// Note that if you want to set the length to a specific number of characters,
// you need to multiply by sizeof(wchar_t). Oddly, there's no public API to
// set the length, so we do this ourselves by hand.
//
// NOTE: The actual allocated size of the BSTR MUST be >= bytes.
// That responsibility is with the caller.
void SetByteLen(uint32 bytes);
// Swap values of two ScopedBstr's.
void Swap(ScopedBstr& bstr2);
// Retrieves the pointer address.
// Used to receive BSTRs as out arguments (and take ownership).
// The function DCHECKs on the current value being NULL.
// Usage: GetBstr(bstr.Receive());
BSTR* Receive();
// Returns number of chars in the BSTR.
uint32 Length() const;
// Returns the number of bytes allocated for the BSTR.
uint32 ByteLength() const;
operator BSTR() const {
return bstr_;
}
protected:
BSTR bstr_;
private:
// Forbid comparison of ScopedBstr types. You should never have the same
// BSTR owned by two different scoped_ptrs.
bool operator==(const ScopedBstr& bstr2) const;
bool operator!=(const ScopedBstr& bstr2) const;
DISALLOW_COPY_AND_ASSIGN(ScopedBstr);
};
// Template class to generate a BSTR from a static wide string
// without touching the heap. Use this class via the StackBstrVar and
// StackBstr macros.
template <uint32 string_bytes>
class StackBstrT {
public:
// Try to stay as const as we can in an attempt to avoid someone
// using the class incorrectly (e.g. by supplying a variable instead
// of a verbatim string. We also have an assert in the constructor
// as an extra runtime check since the const-ness only catches one case.
explicit StackBstrT(const wchar_t* const str) {
// The BSTR API uses UINT, but we prefer uint32.
// Make sure we'll know about it if these types don't match.
COMPILE_ASSERT(sizeof(uint32) == sizeof(UINT), UintToUint32);
COMPILE_ASSERT(sizeof(wchar_t) == sizeof(OLECHAR), WcharToOlechar);
// You shouldn't pass string pointers to this constructor since
// there's no way for the compiler to calculate the length of the
// string (string_bytes will be equal to pointer size in those cases).
DCHECK(lstrlenW(str) == (string_bytes / sizeof(bstr_.str_[0])) - 1) <<
"not expecting a string pointer";
memcpy(bstr_.str_, str, string_bytes);
bstr_.len_ = string_bytes - sizeof(wchar_t);
}
operator BSTR() {
return bstr_.str_;
}
protected:
struct BstrInternal {
uint32 len_;
wchar_t str_[string_bytes / sizeof(wchar_t)];
} bstr_;
};
// Use this macro to generate an inline BSTR from a wide string.
// This is about 6 times faster than using the SysAllocXxx functions to
// allocate a BSTR and helps with keeping heap fragmentation down.
// Example:
// DoBstrStuff(StackBstr(L"This is my BSTR"));
// Where DoBstrStuff is:
// HRESULT DoBstrStuff(BSTR bstr) { ... }
#define StackBstr(str) \
static_cast<BSTR>(StackBstrT<sizeof(str)>(str))
// If you need a named BSTR variable that's based on a fixed string
// (e.g. if the BSTR is used inside a loop or more than one place),
// use StackBstrVar to declare a variable.
// Example:
// StackBstrVar(L"my_property", myprop);
// for (int i = 0; i < objects.length(); ++i)
// ProcessValue(objects[i].GetProp(myprop)); // GetProp accepts BSTR
#define StackBstrVar(str, var) \
StackBstrT<sizeof(str)> var(str)
#endif // BASE_SCOPED_BSTR_WIN_H_
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