c++ - 如何仅包含一次文件/防止 C++ 程序中旧 C API 中的函数重新定义

Question

我有一个 C++ 程序，它必须使用基于 C 的 API 来完成特定任务。如果我在我的程序中只包含一个 cpp，我完全没有问题。但是，如果我包含在头文件中(我需要在其中使用某些类型)，我会收到链接器的重新定义错误。

这是由于在外部库(带有已编译 dll 的 C 头文件)头文件中进行了一些类型定义。我正在寻找这个问题的任何可能的解决方案。

当我搜索所有内容时，我似乎只能找到 header 保护内容(和#pragma once)，但这些都不是问题的解决方案，因为我发现的是单独编译单元中的多个定义，这些定义在链接时会发生冲突.

我在考虑 extern，但发现我无法使用 header 中定义的任何类型作为 C++ 类中的成员，而这正是我想要做的。

Output for building on Warning Level 4
Warning 1   warning C4273: 'getwchar' : inconsistent dll linkage    c:\program files (x86)\microsoft visual studio 11.0\vc\include\stdio.h  615 1   project-test
Warning 2   warning C4273: 'putwchar' : inconsistent dll linkage    c:\program files (x86)\microsoft visual studio 11.0\vc\include\stdio.h  617 1   project-test
Warning 3   warning C4273: 'getwchar' : inconsistent dll linkage    c:\program files (x86)\microsoft visual studio 11.0\vc\include\stdio.h  615 1   project-test
Warning 4   warning C4273: 'putwchar' : inconsistent dll linkage    c:\program files (x86)\microsoft visual studio 11.0\vc\include\stdio.h  617 1   project-test
Warning 5   warning C4100: 'data' : unreferenced formal parameter   c:\users\ian\skydrive\documents\uni\finpro\projects\project-test\project-test\main.cpp  8   1   project-test
Warning 6   warning C4100: 'event' : unreferenced formal parameter  c:\users\ian\skydrive\documents\uni\finpro\projects\project-test\project-test\main.cpp  8   1   project-test
Warning 7   warning C4100: 'widget' : unreferenced formal parameter c:\users\ian\skydrive\documents\uni\finpro\projects\project-test\project-test\main.cpp  8   1   project-test
Warning 8   warning C4100: 'data' : unreferenced formal parameter   c:\users\ian\skydrive\documents\uni\finpro\projects\project-test\project-test\main.cpp  15  1   project-test
Warning 9   warning C4100: 'event' : unreferenced formal parameter  c:\users\ian\skydrive\documents\uni\finpro\projects\project-test\project-test\main.cpp  15  1   project-test
Warning 10  warning C4100: 'widget' : unreferenced formal parameter c:\users\ian\skydrive\documents\uni\finpro\projects\project-test\project-test\main.cpp  15  1   project-test
Warning 11  warning C4505: 'g_bit_nth_lsf' : unreferenced local function has been removed   c:\users\ian\skydrive\documents\uni\finpro\gtk\include\glib-2.0\glib\gutils.h   267 1   project-test
Warning 12  warning C4505: 'g_bit_nth_msf' : unreferenced local function has been removed   c:\users\ian\skydrive\documents\uni\finpro\gtk\include\glib-2.0\glib\gutils.h   269 1   project-test
Warning 13  warning C4505: 'g_bit_storage' : unreferenced local function has been removed   c:\users\ian\skydrive\documents\uni\finpro\gtk\include\glib-2.0\glib\gutils.h   271 1   project-test
Warning 14  warning C4505: 'g_string_append_c_inline' : unreferenced local function has been removed    c:\users\ian\skydrive\documents\uni\finpro\gtk\include\glib-2.0\glib\gstring.h  130 1   project-test
Warning 15  warning C4505: 'g_trash_stack_push' : unreferenced local function has been removed  c:\users\ian\skydrive\documents\uni\finpro\gtk\include\glib-2.0\glib\gtrashstack.h  44  1   project-test
Warning 16  warning C4505: 'g_trash_stack_pop' : unreferenced local function has been removed   c:\users\ian\skydrive\documents\uni\finpro\gtk\include\glib-2.0\glib\gtrashstack.h  46  1   project-test
Warning 17  warning C4505: 'g_trash_stack_peek' : unreferenced local function has been removed  c:\users\ian\skydrive\documents\uni\finpro\gtk\include\glib-2.0\glib\gtrashstack.h  47  1   project-test
Warning 18  warning C4505: 'g_trash_stack_height' : unreferenced local function has been removed    c:\users\ian\skydrive\documents\uni\finpro\gtk\include\glib-2.0\glib\gtrashstack.h  48  1   project-test
Error   19  error LNK2005: "long __cdecl abs(long)" (?abs@@YAJJ@Z) already defined in FitsFile.obj  C:\Users\Ian\SkyDrive\Documents\Uni\FINPRO\projects\project-test\project-test\main.obj  project-test
Error   20  error LNK2005: "__int64 __cdecl abs(__int64)" (?abs@@YA_J_J@Z) already defined in FitsFile.obj  C:\Users\Ian\SkyDrive\Documents\Uni\FINPRO\projects\project-test\project-test\main.obj  project-test
Error   21  error LNK2005: "struct _ldiv_t __cdecl div(long,long)" (?div@@YA?AU_ldiv_t@@JJ@Z) already defined in FitsFile.obj   C:\Users\Ian\SkyDrive\Documents\Uni\FINPRO\projects\project-test\project-test\main.obj  project-test
Error   22  error LNK2005: "struct _lldiv_t __cdecl div(__int64,__int64)" (?div@@YA?AU_lldiv_t@@_J0@Z) already defined in FitsFile.obj  C:\Users\Ian\SkyDrive\Documents\Uni\FINPRO\projects\project-test\project-test\main.obj  project-test
Error   23  error LNK2005: _getwchar already defined in FitsFile.obj    C:\Users\Ian\SkyDrive\Documents\Uni\FINPRO\projects\project-test\project-test\main.obj  project-test
Error   24  error LNK2005: _putwchar already defined in FitsFile.obj    C:\Users\Ian\SkyDrive\Documents\Uni\FINPRO\projects\project-test\project-test\main.obj  project-test
Error   25  error LNK1169: one or more multiply defined symbols found   C:\Users\Ian\SkyDrive\Documents\Uni\FINPRO\projects\project-test\Debug\project-test.exe project-test

Output for building on Warning Level 4 (when only including for one place)
Warning 1   warning C4273: 'getwchar' : inconsistent dll linkage    c:\program files (x86)\microsoft visual studio 11.0\vc\include\stdio.h  615 1   project-test
Warning 2   warning C4273: 'putwchar' : inconsistent dll linkage    c:\program files (x86)\microsoft visual studio 11.0\vc\include\stdio.h  617 1   project-test
Warning 3   warning C4100: 'data' : unreferenced formal parameter   c:\users\ian\skydrive\documents\uni\finpro\projects\project-test\project-test\main.cpp  8   1   project-test
Warning 4   warning C4100: 'event' : unreferenced formal parameter  c:\users\ian\skydrive\documents\uni\finpro\projects\project-test\project-test\main.cpp  8   1   project-test
Warning 5   warning C4100: 'widget' : unreferenced formal parameter c:\users\ian\skydrive\documents\uni\finpro\projects\project-test\project-test\main.cpp  8   1   project-test
Warning 6   warning C4100: 'data' : unreferenced formal parameter   c:\users\ian\skydrive\documents\uni\finpro\projects\project-test\project-test\main.cpp  15  1   project-test
Warning 7   warning C4100: 'event' : unreferenced formal parameter  c:\users\ian\skydrive\documents\uni\finpro\projects\project-test\project-test\main.cpp  15  1   project-test
Warning 8   warning C4100: 'widget' : unreferenced formal parameter c:\users\ian\skydrive\documents\uni\finpro\projects\project-test\project-test\main.cpp  15  1   project-test
Warning 9   warning C4505: 'g_bit_nth_lsf' : unreferenced local function has been removed   c:\users\ian\skydrive\documents\uni\finpro\gtk\include\glib-2.0\glib\gutils.h   267 1   project-test
Warning 10  warning C4505: 'g_bit_nth_msf' : unreferenced local function has been removed   c:\users\ian\skydrive\documents\uni\finpro\gtk\include\glib-2.0\glib\gutils.h   269 1   project-test
Warning 11  warning C4505: 'g_bit_storage' : unreferenced local function has been removed   c:\users\ian\skydrive\documents\uni\finpro\gtk\include\glib-2.0\glib\gutils.h   271 1   project-test
Warning 12  warning C4505: 'g_string_append_c_inline' : unreferenced local function has been removed    c:\users\ian\skydrive\documents\uni\finpro\gtk\include\glib-2.0\glib\gstring.h  130 1   project-test
Warning 13  warning C4505: 'g_trash_stack_push' : unreferenced local function has been removed  c:\users\ian\skydrive\documents\uni\finpro\gtk\include\glib-2.0\glib\gtrashstack.h  44  1   project-test
Warning 14  warning C4505: 'g_trash_stack_pop' : unreferenced local function has been removed   c:\users\ian\skydrive\documents\uni\finpro\gtk\include\glib-2.0\glib\gtrashstack.h  46  1   project-test
Warning 15  warning C4505: 'g_trash_stack_peek' : unreferenced local function has been removed  c:\users\ian\skydrive\documents\uni\finpro\gtk\include\glib-2.0\glib\gtrashstack.h  47  1   project-test
Warning 16  warning C4505: 'g_trash_stack_height' : unreferenced local function has been removed    c:\users\ian\skydrive\documents\uni\finpro\gtk\include\glib-2.0\glib\gtrashstack.h  48  1   project-test

Answer 1

抽象出间接层背后的 C 功能:

原始结构(如果我理解正确的话，这就是你现在的结构):

file1.h -> #include included_c_api.h
file2.h -> #include included_c_api.h CAUSES errors.

新结构:

new_c_api.h -> wrapper over included_c_api.h functionality (w/ your own symbols)
new_c_api.c[pp] -> #include included_c_api.h
file1.h -> #include new_c_api.h
file2.h -> #include new_c_api.h

如果 included_c_api.h 中公开的功能非常大，则此解决方案可能不切实际。