错误重现：
--------------------Configuration: curl - Win32 LIB Debug DLL Windows SSPI DLL WinIDN-------------------- xilink6: executing 'D:\vc6.0\VC98\Bin\link.exe'
libcurld.lib(idn_win32.obj) : error LNK2001: unresolved external symbol __imp__IdnToAscii@
libcurld.lib(idn_win32.obj) : error LNK2001: unresolved external symbol __imp__IdnToUnicode@
..\..\..\..\build\Win32\VC6\LIB Debug - DLL Windows SSPI - DLL WinIDN\curld.exe : fatal error LNK1120: unresolved externals
Error executing xilink6.exe. curld.exe - error(s), warning(s) --------------------Configuration: curl - Win32 LIB Release DLL Windows SSPI DLL WinIDN--------------------
Linking...
xilink6: executing 'D:\vc6.0\VC98\Bin\link.exe'
libcurl.lib(idn_win32.obj) : error LNK2001: unresolved external symbol __imp__IdnToAscii@
libcurl.lib(idn_win32.obj) : error LNK2001: unresolved external symbol __imp__IdnToUnicode@
..\..\..\..\build\Win32\VC6\LIB Release - DLL Windows SSPI - DLL WinIDN/curl.exe : fatal error LNK1120: 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_FOLDER\lib\idn_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(, in_w, -, 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) + ;
wchar_t unicode[IDN_MAX_LENGTH];
int chars = IdnToUnicode(, 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 = -;
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(, in_w, -, 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) + ;
wchar_t unicode[IDN_MAX_LENGTH];
int chars = -;
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(, 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。