This topic describes the tools available for you to use in making your application 64-bit ready.
The API elements are virtually identical between 32- and 64-bit Windows. The Windows header files have been modified so that they can be used for both 32- and 64-bit code. The new 64-bit types and macros are defined in a new header file, Basetsd.h, which is in the set of header files included by Windows.h. Basetsd.h includes the new data-type definitions to assist in making source code word-size independent.
The Windows header files contain new data types. These types are primarily for type compatibility with the 32-bit data types. The new types provide exactly the same typing as the existing types, while at the same time providing support for the 64-bit Windows. For more information, see The New Data Types or the Basetsd.h header file.
The compiler defines the following macros to identify the platform.
|_WIN64||A 64-bit platform.|
|_WIN32||A 32-bit platform.
This value is also defined by the 64-bit compiler for backward compatibility.
|_WIN16||A 16-bit platform|
The following macros are specific to the architecture.
|_M_IA64||Intel Itanium platform|
Do not use these macros except with architecture-specific code, instead, use _WIN64, _WIN32, and _WIN16 whenever possible.
The following inline functions (defined in Basetsd.h) can help you safely convert values from one type to another.
void * Handle64ToHandle( const void * POINTER_64 h ) void * POINTER_64 HandleToHandle64( const void *h ) long HandleToLong( const void *h ) unsigned long HandleToUlong( const void *h ) void * IntToPtr( const int i ) void * LongToHandle( const long h ) void * LongToPtr( const long l ) void * Ptr64ToPtr( const void * POINTER_64 p ) int PtrToInt( const void *p ) long PtrToLong( const void *p ) void * POINTER_64 PtrToPtr64( const void *p ) short PtrToShort( const void *p ) unsigned int PtrToUint( const void *p ) unsigned long PtrToUlong( const void *p ) unsigned short PtrToUshort( const void *p ) void * UIntToPtr( const unsigned int ui ) void * ULongToPtr( const unsigned long ul )
Warning IntToPtr sign-extends the int value, UIntToPtr zero-extends the unsigned int value, LongToPtr sign-extends the long value, and ULongToPtr zero-extends the unsigned long value.
The 64-bit compilers can be used to identify pointer truncation, improper type casts, and other 64-bit-specific problems.
When the compiler is first run, it will probably generate many pointer truncation or type mismatch warnings, such as the following:
warning C4311: 'type cast' : pointer truncation from 'unsigned char *' to 'unsigned long '
Use these warnings as a guide to make the code more robust. It is good practice to eliminate all warnings, especially pointer-truncation warnings.
Note that this compiler enables the LLP64 data model.
There is a warning option to assist porting to LLP64. The -Wp64 -W3 switch enables the following warnings:
- C4305: Truncation warning. For example, "return": truncation from "unsigned int64" to "long."
- C4311: Truncation warning. For example, "type cast": pointer truncation from "int*_ptr64" to "int."
- C4312: Conversion to bigger-size warning. For example, "type cast": conversion from "int" to "int*_ptr64" of greater size.
- C4318: Passing zero length. For example, passing constant zero as the length to the memset function.
- C4319: Not operator. For example, "~": zero extending "unsigned long" to "unsigned _int64" of greater size.
- C4313: Calling the printf family of functions with conflicting conversion type specifiers and arguments. For example, "printf": "%p" in format string conflicts with argument 2 of type "_int64." Another example is the call printf("%x", pointer_value); this causes a truncation of the upper 32 bits. The correct call is printf("%p", pointer_value).
- C4244: Same as the existing warning C4242. For example, "return": conversion from "_int64" to "unsigned int," possible loss of data.
To build applications, use the linker and libraries provided by the Windows SDK. Most 32-bit libraries have a corresponding 64-bit version, but certain legacy libraries are available only in 32-bit versions. Code that calls into these libraries will not link when the application is built for 64-bit Windows.