我刚刚检查过LoadImage http://msdn.microsoft.com/en-us/library/windows/desktop/ms648045%28v=vs.85%29.aspx确实支持通过标志从文件加载LR_LOADFROMFILE.
所以这将是我的第一选择。
次要选择，GDI+（请注意，它需要大量摆弄初始化内容才能获得普通的良好质量，并且至少几年前它仍然依赖于min and max macros from <windows.h>）。第三个选择，Windows 映像组件 http://msdn.microsoft.com/en-us/library/windows/desktop/ee719654%28v=vs.85%29.aspx在对该问题的评论中提到。第四个选择，OleLoadPicturePath http://msdn.microsoft.com/en-us/library/windows/desktop/ms678485%28v=vs.85%29.aspx和家人。
Addendum: 正如评论中所指出的LoadImage仅限于加载图像文件的“位图”。在我的系统上，下面的测试程序报告 .bmp 文件加载正常，但 .gif、.png 和 .jpg 文件加载失败。
#undef UNICODE
#define UNICODE
#include <windows.h>
#include <assert.h> // assert
#include <iostream> // std::wcout
#include <string> // std::wstring
using namespace std;
auto get_exe_path()
-> wstring
{
int const buffer_size = MAX_PATH;
wstring result( buffer_size, L'#' );
int const n_characters = GetModuleFileName( 0, &result[0], buffer_size );
assert( 0 < n_characters && n_characters < buffer_size );
result.resize( n_characters );
return result;
}
auto get_exe_folder_path()
-> wstring
{
wstring const exe_path = get_exe_path();
int const i = exe_path.rfind( L'\\' );
return exe_path.substr( 0, i + 1 );
}
void test( wstring const& image_name )
{
wstring const image_file_name = get_exe_folder_path() + image_name;
wcout << image_file_name << endl;
HANDLE const image = ::LoadImage(
0, // HINSTANCE hinst,
image_file_name.c_str(),
IMAGE_BITMAP,
0, 0, // int cxDesired, int cyDesired,
LR_LOADFROMFILE
);
wcout << image << endl;
DeleteObject( image );
}
auto main()
-> int
{
test( L"test.bmp" ); wcout << endl;
test( L"test.png" ); wcout << endl;
test( L"test.gif" ); wcout << endl;
test( L"test.jpg" );
}
附录2：为了检查一下，我还测试了 Windows 成像组件功能，它确实可以处理上述所有四种图像类型。下面代码的大部分大小是由于对 COM 的可重用一次写入支持（我只是再次从头开始编写它，所以它有点粗略，只是这里需要的）。不过，此代码不会显示图像或对其执行任何其他操作，而 WIC 也同样复杂......
虽然这段代码有部分 g++ 支持，但我已经用 g++ 对其进行了测试。我记得 g++ 仅支持 Windows API，就像 Windows XP 一样。我不确定 WIC 何时引入（尽管它可以与 Windows XP 一起使用）。
#undef UNICODE
#define UNICODE
#include <windows.h>
#include <wincodec.h> // IWICImagingFactory
#include <algorithm> // std::swap
#include <assert.h> // assert
#include <iostream> // std::wcout
#include <stdlib.h> // EXIT_FAILURE, EXIT_SUCCESS
#include <string> // std::string, std::wstring
#include <utility> // std::move
#ifndef CPPX_NOEXCEPT
# if defined( _MSC_VER )
# define CPPX_NOEXCEPT throw()
# else
# define CPPX_NOEXCEPT noexcept
# endif
#endif
#ifndef CPPX_NORETURN
# if defined( _MSC_VER )
# define CPPX_NORETURN __declspec( noreturn )
# pragma warning( disable: 4646 ) // "has non-void return type"
# elif defined( __GNUC__ )
# define CPPX_NORETURN __attribute__((noreturn))
# else
# define CPPX_NORETURN [[noreturn]]
# endif
#endif
namespace cppx {
using std::string;
using std::runtime_error;
auto hopefully( bool const condition )
CPPX_NOEXCEPT
-> bool
{ return condition; }
CPPX_NORETURN
auto fail( string const& s )
-> bool
{ throw runtime_error( s ); }
} // namespace cppx
namespace process {
using std::wstring;
auto get_exe_path()
-> wstring
{
int const buffer_size = MAX_PATH;
wstring result( buffer_size, L'#' );
int const n_characters = GetModuleFileName( 0, &result[0], buffer_size );
assert( 0 < n_characters && n_characters < buffer_size );
result.resize( n_characters );
return result;
}
auto get_exe_folder_path()
-> wstring
{
wstring const exe_path = get_exe_path();
int const i = exe_path.rfind( L'\\' );
return exe_path.substr( 0, i + 1 );
}
} // namespace process
namespace com {
using cppx::fail;
using std::move;
enum Success { success };
auto operator>>( HRESULT const hr, Success )
-> bool
{ return SUCCEEDED( hr ); }
struct Library
{
~Library()
{ CoUninitialize(); }
Library()
{ CoInitialize( nullptr ); }
};
template< class Interface >
class Ptr
{
private:
Interface* p_;
public:
auto raw() -> Interface* { return p_; }
auto operator->() -> Interface* { return p_; }
void clear() { Ptr null; swap( *this, null ); }
auto as_value_receiver()
-> Interface**
{
clear();
return &p_;
}
auto as_untyped_value_receiver()
-> void**
{ return reinterpret_cast<void**>( as_value_receiver() ); }
friend void swap( Ptr& a, Ptr& b )
CPPX_NOEXCEPT
{ std::swap( a.p_, b.p_ ); }
void operator=( Ptr other )
{ swap( *this, other ); }
void operator=( Ptr&& other )
{
Ptr temp( move( other ) );
swap( temp, *this );
}
~Ptr()
{ if( p_ != nullptr ) { p_->Release(); } }
explicit Ptr( Interface* p = nullptr )
CPPX_NOEXCEPT
: p_( p )
{}
Ptr( Ptr const& other )
: p_( other.p_ )
{ if( p != nullptr ) { p_->AddRef(); } }
Ptr( Ptr&& other )
CPPX_NOEXCEPT
: p_( other.p_ )
{ other.p_ = nullptr; }
static
auto create_local( CLSID const& class_id )
-> Ptr<Interface>
{
Ptr<Interface> result;
::CoCreateInstance(
class_id, nullptr, CLSCTX_INPROC_SERVER,
__uuidof( Interface ),
result.as_untyped_value_receiver()
)
>> success
|| fail( "CoCreateInstance" );
return move( result );
}
};
} // namespace com
namespace app {
using cppx::fail;
using std::wstring;
using std::wcout; using std::endl;
void test( wstring const& image_name )
{
wstring const image_file_name =
process::get_exe_folder_path() + image_name;
wcout << image_file_name << endl;
auto p_factory =
com::Ptr<IWICImagingFactory>::create_local( CLSID_WICImagingFactory );
com::Ptr< IWICBitmapDecoder> p_decoder;
p_factory->CreateDecoderFromFilename(
image_file_name.c_str(),
nullptr,
GENERIC_READ,
WICDecodeMetadataCacheOnDemand, // Cache metadata when needed
p_decoder.as_value_receiver()
)
>> com::success
|| fail( "IWICImagingFactory::CreateDecoderFromFilename" );
com::Ptr<IWICBitmapFrameDecode> p_frame;
p_decoder->GetFrame( 0, p_frame.as_value_receiver() )
>> com::success
|| fail( "IWICBitmapFrameDecode::GetFrame");
UINT w, h;
p_frame->GetSize( &w, &h )
>> com::success
|| fail( "IWICBitmapFrameDecode::GetSize" );
wcout << "(w, h) = (" << w << ", " << h << ")" << endl;
}
void cpp_main()
{
com::Library const com_usage;
test( L"test.bmp" ); wcout << endl;
test( L"test.png" ); wcout << endl;
test( L"test.gif" ); wcout << endl;
test( L"test.jpg" ); wcout << endl;
test( L"test.bogus" );
}
} // namespace app
auto main()
-> int
{
using namespace std;
try
{
app::cpp_main();
return EXIT_SUCCESS;
}
catch( exception const& x )
{
wcout << "!" << x.what() << endl;
}
return EXIT_FAILURE;
}
