Visual Studio C++ 2010 链接错误

Question

我收到几个 error LNK2019: unresolved external symbol 错误，但它们不是由 dll、lib 或 OO 错误引起的正如关于此链接错误的所有其他 StackOverflow 帖子一样。

代码：

https://github.com/mcandre/fgdump/tree/master/cachedump

跟踪：

1>------ Build started: Project: cachedump, Configuration: Release Win32 ------
1>LINK : warning LNK4075: ignoring '/INCREMENTAL' due to '/OPT:ICF' specification
1>cachedump.obj : error LNK2019: unresolved external symbol "void __cdecl rc4_crypt(struct rc4_state *,unsigned char *,int)" (?rc4_crypt@@YAXPAUrc4_state@@PAEH@Z) referenced in function "unsigned long __cdecl DumpCache(void)" (?DumpCache@@YAKXZ)
1>cachedump.obj : error LNK2019: unresolved external symbol "void __cdecl rc4_setup(struct rc4_state *,unsigned char *,int)" (?rc4_setup@@YAXPAUrc4_state@@PAEH@Z) referenced in function "unsigned long __cdecl DumpCache(void)" (?DumpCache@@YAKXZ)
1>cachedump.obj : error LNK2019: unresolved external symbol "void __cdecl md5_finish(struct md5_context *,unsigned char * const)" (?md5_finish@@YAXPAUmd5_context@@QAE@Z) referenced in function "unsigned long __cdecl DumpCache(void)" (?DumpCache@@YAKXZ)
1>cachedump.obj : error LNK2019: unresolved external symbol "void __cdecl md5_update(struct md5_context *,unsigned char *,unsigned long)" (?md5_update@@YAXPAUmd5_context@@PAEK@Z) referenced in function "unsigned long __cdecl DumpCache(void)" (?DumpCache@@YAKXZ)
1>cachedump.obj : error LNK2019: unresolved external symbol "void __cdecl md5_starts(struct md5_context *)" (?md5_starts@@YAXPAUmd5_context@@@Z) referenced in function "unsigned long __cdecl DumpCache(void)" (?DumpCache@@YAKXZ)
1>C:\Users\andrew\Desktop\src\fgdump\cachedump\Release\cachedump.exe : fatal error LNK1120: 5 unresolved externals
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

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Answer 1

.c 文件由 cl 编译为 C 代码，而 .cpp 文件则编译为 C++代码。由于 C 和 C++ 代码中符号定义的差异，您的 C++ 代码无法看到 C 代码中的函数。

在标头中使用 extern "C" 包装器，或者最好在整个项目中使用相同的语言

要使 extern "C" 包装器使用以下模板

#ifdef __cplusplus
extern "C"
{
#endif

//put C-function declarations here    

#ifdef __cplusplus
}
#endif