l我正在尝试在程序中使用libpng，在Windows Mobile 6.1上工作。
为此，我从模板“c++ SmartDevice Class library”创建了一个 c++ 项目，并使用那里提供的 Visual Studio 项目作为指南，从 libpng 添加了适当的 c 源文件，并将 libpng 源的目录添加到源搜索目录。
但是，当我尝试编译时，出现以下错误：
error C2054: expected '(' to follow 'PNG_DLL_EXPORT' <path>\lib\lpng1512\png.h 991
换句话说，首先 PNG_DLL_EXPORT 会导致错误，然后在 png.h 的每一行中都会出现错误。
原因是什么？这应该如何解决？这是一个已知问题吗？
更新：那里使用的确切宏是 PNG_EXPORT。它在 pngconf.h 中定义为：
#define PNG_EXPORT(ordinal, type, name, args)\
PNG_EXPORTA(ordinal, type, name, args, PNG_EMPTY)
因此，使用的宏定义为：
/* ANSI-C (C90) does not permit a macro to be invoked with an empty argument,
* so make something non-empty to satisfy the requirement:
*/
#define PNG_EMPTY /*empty list*/
和
/* The ordinal value is only relevant when preprocessing png.h for symbol
* table entries, so we discard it here. See the .dfn files in the
* scripts directory.
*/
#ifndef PNG_EXPORTA
# define PNG_EXPORTA(ordinal, type, name, args, attributes)\
PNG_FUNCTION(PNG_EXPORT_TYPE(type),(PNGAPI name),PNGARG(args), \
extern attributes)
#endif
在兔子洞下面，有：
/* In 1.5.2 the definition of PNG_FUNCTION has been changed to always treat
* 'attributes' as a storage class - the attributes go at the start of the
* function definition, and attributes are always appended regardless of the
* compiler. This considerably simplifies these macros but may cause problems
* if any compilers both need function attributes and fail to handle them as
* a storage class (this is unlikely.)
*/
#ifndef PNG_FUNCTION
# define PNG_FUNCTION(type, name, args, attributes) attributes type name args
#endif
#ifndef PNG_EXPORT_TYPE
# define PNG_EXPORT_TYPE(type) PNG_IMPEXP type
#endif
再往下：
# if (defined(_MSC_VER) && _MSC_VER < 800) ||\
(defined(__BORLANDC__) && __BORLANDC__ < 0x500)
/* older Borland and MSC
* compilers used '__export' and required this to be after
* the type.
*/
# ifndef PNG_EXPORT_TYPE
# define PNG_EXPORT_TYPE(type) type PNG_IMPEXP
# endif
# define PNG_DLL_EXPORT __export
# else /* newer compiler */
# define PNG_DLL_EXPORT __declspec(dllexport)
# ifndef PNG_DLL_IMPORT
# define PNG_DLL_IMPORT __declspec(dllimport)
# endif
# endif /* compiler */
在其他文件中，pngpriv.h，PNG_DLL_EXPORT 最终被使用：
/* See pngconf.h for more details: the builder of the library may set this on
* the command line to the right thing for the specific compilation system or it
* may be automagically set above (at present we know of no system where it does
* need to be set on the command line.)
*
* PNG_IMPEXP must be set here when building the library to prevent pngconf.h
* setting it to the "import" setting for a DLL build.
*/
#ifndef PNG_IMPEXP
# ifdef PNG_BUILD_DLL
# define PNG_IMPEXP PNG_DLL_EXPORT
# else
/* Not building a DLL, or the DLL doesn't require specific export
* definitions.
*/
# define PNG_IMPEXP
# endif
#endif
Update2：这个问题是特定于编译成 dll 的。编译成 lib 不会导致相同的编译器错误。