错误重现：
--------------------Configuration: curl - Win32 LIB Debug DLL Windows SSPI DLL WinIDN-------------------- xilink6: executing 'D:vc6.0VC98Binlink.exe' libcurld.lib(idn_win32.obj) : error LNK2001: unresolved external symbol __imp__IdnToAscii@20 libcurld.lib(idn_win32.obj) : error LNK2001: unresolved external symbol __imp__IdnToUnicode@20 ........uildWin32VC6LIB Debug - DLL Windows SSPI - DLL WinIDNcurld.exe : fatal error LNK1120: 2 unresolved externals Error executing xilink6.exe. curld.exe - 3 error(s), 2 warning(s) --------------------Configuration: curl - Win32 LIB Release DLL Windows SSPI DLL WinIDN-------------------- Linking... xilink6: executing 'D:vc6.0VC98Binlink.exe' libcurl.lib(idn_win32.obj) : error LNK2001: unresolved external symbol __imp__IdnToAscii@20 libcurl.lib(idn_win32.obj) : error LNK2001: unresolved external symbol __imp__IdnToUnicode@20 ........uildWin32VC6LIB Release - DLL Windows SSPI - DLL WinIDN/curl.exe : fatal error LNK1120: 2 unresolved externals
根据两个API的名字google了一下
IdnToUnicode,IdnToAscii封装在normaliz.dll中，查询了本机的几个SDK(Microsoft Platform SDK February 2003,Microsoft Windows SDK v6.0A,Microsoft Windows SDK v7.0A,
Microsoft Windows SDK v7.1),只有Microsoft Platform SDK February 2003没有，心想这下坏了，不好编译了，因为Microsoft Platform SDK February 2003是Windows XP最终版SDK，翻了一下%systemroot%system32又可以找到normaliz.dll,查看了一下导出函数，又是有的，不懂什么软件带过来的，还是系统更新装上的。
msdn对IdnToUnicode,IdnToAscii这两个函数的使用要求如下:
|
Minimum supported client |
Windows Vista [desktop apps | Windows Store apps] |
|---|---|
|
Minimum supported server |
Windows Server 2008 [desktop apps | Windows Store apps] |
|
Redistributable |
Microsoft Internationalized Domain Name (IDN) Mitigation APIs onWindows XP with SP2 and later,Windows Server 2003 with SP1 |
|
Header |
|
|
Library |
|
|
DLL |
|
从以上表格看出，这个库一开始并不是为Windows XP准备的，只是后来在SP2以后才有，用VC++6.0编译的时候normaliz.lib指向的dll函数地址就是错误的,
于是想到用LoadLibrary和GetProcAddress函数配合，显式调用者两个函数，从这个程度上来说也可以节省内存开销，使用完立即释放掉。
解决办法:
问题的根源是idn,于是找到了CURL_FOLDERlibidn_win32.c进行开刀。
以下是7.50.3版本的idn_win32.c修改前的模样:
#include "curl_setup.h" #ifdef USE_WIN32_IDN #include "curl_multibyte.h" #include "curl_memory.h" #include "warnless.h" /* The last #include file should be: */ #include "memdebug.h" #ifdef WANT_IDN_PROTOTYPES # if defined(_SAL_VERSION) WINNORMALIZEAPI int WINAPI IdnToAscii(_In_ DWORD dwFlags, _In_reads_(cchUnicodeChar) LPCWSTR lpUnicodeCharStr, _In_ int cchUnicodeChar, _Out_writes_opt_(cchASCIIChar) LPWSTR lpASCIICharStr, _In_ int cchASCIIChar); WINNORMALIZEAPI int WINAPI IdnToUnicode(_In_ DWORD dwFlags, _In_reads_(cchASCIIChar) LPCWSTR lpASCIICharStr, _In_ int cchASCIIChar, _Out_writes_opt_(cchUnicodeChar) LPWSTR lpUnicodeCharStr, _In_ int cchUnicodeChar); # else WINBASEAPI int WINAPI IdnToAscii(DWORD dwFlags, const WCHAR *lpUnicodeCharStr, int cchUnicodeChar, WCHAR *lpASCIICharStr, int cchASCIIChar); WINBASEAPI int WINAPI IdnToUnicode(DWORD dwFlags, const WCHAR *lpASCIICharStr, int cchASCIIChar, WCHAR *lpUnicodeCharStr, int cchUnicodeChar); # endif #endif #define IDN_MAX_LENGTH 255 bool curl_win32_idn_to_ascii(const char *in, char **out); bool curl_win32_ascii_to_idn(const char *in, char **out); bool curl_win32_idn_to_ascii(const char *in, char **out) { bool success = FALSE; wchar_t *in_w = Curl_convert_UTF8_to_wchar(in); if(in_w) { wchar_t punycode[IDN_MAX_LENGTH]; int chars = IdnToAscii(0, in_w, -1, punycode, IDN_MAX_LENGTH); free(in_w); if(chars) { *out = Curl_convert_wchar_to_UTF8(punycode); if(*out) success = TRUE; } } return success; } bool curl_win32_ascii_to_idn(const char *in, char **out) { bool success = FALSE; wchar_t *in_w = Curl_convert_UTF8_to_wchar(in); if(in_w) { size_t in_len = wcslen(in_w) + 1; wchar_t unicode[IDN_MAX_LENGTH]; int chars = IdnToUnicode(0, in_w, curlx_uztosi(in_len), unicode, IDN_MAX_LENGTH); free(in_w); if(chars) { *out = Curl_convert_wchar_to_UTF8(unicode); if(*out) success = TRUE; } } return success; } #endif /* USE_WIN32_IDN */
idn_win32.c修改后的模样:
#include "curl_setup.h" #ifdef USE_WIN32_IDN #include "curl_multibyte.h" #include "curl_memory.h" #include "warnless.h" /* The last #include file should be: */ #include "memdebug.h" #ifdef WANT_IDN_PROTOTYPES //# if defined(_SAL_VERSION) typedef int (*fnIdnToAscii)(DWORD,const WCHAR *,int,WCHAR *,int); typedef int (*fnIdnToUnicode)(DWORD,const WCHAR *,int,WCHAR *, int); //# endif #endif #define IDN_MAX_LENGTH 255 bool curl_win32_idn_to_ascii(const char *in, char **out); bool curl_win32_ascii_to_idn(const char *in, char **out); bool curl_win32_idn_to_ascii(const char *in, char **out) { bool success = FALSE; wchar_t *in_w = Curl_convert_UTF8_to_wchar(in); if(in_w) { wchar_t punycode[IDN_MAX_LENGTH]; int chars = -1; fnIdnToAscii IdnToAscii; HINSTANCE hNormalizDLL = LoadLibrary("normaliz.dll"); if (!hNormalizDLL) { FreeLibrary(hNormalizDLL); assert(hNormalizDLL); return FALSE; } IdnToAscii = (fnIdnToAscii)GetProcAddress(hNormalizDLL, "IdnToAscii"); if (!IdnToAscii) { assert(IdnToAscii); return TRUE; } chars = IdnToAscii(0, in_w, -1, punycode, IDN_MAX_LENGTH); free(IdnToAscii); FreeLibrary(hNormalizDLL); free(in_w); if(chars) { *out = Curl_convert_wchar_to_UTF8(punycode); if(*out) success = TRUE; } } return success; } bool curl_win32_ascii_to_idn(const char *in, char **out) { bool success = FALSE; wchar_t *in_w = Curl_convert_UTF8_to_wchar(in); if(in_w) { size_t in_len = wcslen(in_w) + 1; wchar_t unicode[IDN_MAX_LENGTH]; int chars = -1; fnIdnToUnicode IdnToUnicode; HINSTANCE hNormalizDLL = LoadLibrary("normaliz.dll"); if (!hNormalizDLL) { FreeLibrary(hNormalizDLL); assert(hNormalizDLL); return FALSE; } IdnToUnicode = (fnIdnToUnicode)GetProcAddress(hNormalizDLL, "IdnToUnicode"); if (!IdnToUnicode) { assert(IdnToUnicode); return FALSE; } chars = IdnToUnicode(0, in_w, curlx_uztosi(in_len), unicode, IDN_MAX_LENGTH); free(IdnToUnicode); FreeLibrary(hNormalizDLL); free(in_w); if(chars) { *out = Curl_convert_wchar_to_UTF8(unicode); if(*out) success = TRUE; } } return success; } #endif /* USE_WIN32_IDN */
经过以上修改就可以编译成功了。