菜鸟送分－关于DLL的初级知识

[zhutoucoding]

小弟刚刚开始学写DLL，昨天按照MSDN写了一个很简单的DLL，但是调用的时候却说找不到断口（GetLastError()=127），不知道为什么，各位给我的小程序找找毛病吧，谢谢！

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调用DLL的测试代码
-----------------------------------------------------------------------
// File: RUNTIME.C
// A simple program that uses LoadLibrary and
// GetProcAddress to access myPuts from MYPUTS.DLL.

#include <stdio.h>
#include <windows.h>

typedef VOID (*MYPROC)(LPTSTR);

VOID main(VOID)
{
HINSTANCE hinstLib;
MYPROC ProcAdd;
BOOL fFreeResult, fRunTimeLinkSuccess = FALSE;

// Get a handle to the DLL module.
hinstLib = LoadLibrary("myputs");

// If the handle is valid, try to get the function address.
if (hinstLib != NULL)
{
ProcAdd = (MYPROC) GetProcAddress(hinstLib, "myPuts");

// If the function address is valid, call the function.
if (fRunTimeLinkSuccess = (ProcAdd != NULL))
{
(ProcAdd) ("Hello, World!\n");
}
else
{
printf("Error = %ld\n",GetLastError());
}
// Free the DLL module.
fFreeResult = FreeLibrary(hinstLib);
}

// If unable to call the DLL function, use an alternative.
if (! fRunTimeLinkSuccess)
printf("message via alternative method\n");
}
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DLL头文件
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myputs.h
-----------------------------------------------------------------------
#ifdef MYPUTS_EXPORTS
#define MYPUTS_API __declspec(dllexport)
#else
#define MYPUTS_API __declspec(dllimport)
#endif

MYPUTS_API void myPuts(LPTSTR lpszMsg);
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stdafx.h
-----------------------------------------------------------------------
#if !defined(AFX_STDAFX_H__202DBB33_8EE9_4155_A30F_6CA38D34C9BF__INCLUDED_)
#define AFX_STDAFX_H__202DBB33_8EE9_4155_A30F_6CA38D34C9BF__INCLUDED_

#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000

#include <windows.h>

#endif // !defined(AFX_STDAFX_H__202DBB33_8EE9_4155_A30F_6CA38D34C9BF__INCLUDED_)
-----------------------------------------------------------------------
DLL 代码
-----------------------------------------------------------------------
stdafx.cpp
-----------------------------------------------------------------------
#include "stdafx.h"
-----------------------------------------------------------------------
MyPuts.cpp
-----------------------------------------------------------------------
#include "stdafx.h"
#include "MyPuts.h"

BOOL APIENTRY DllMain( HANDLE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{
switch (ul_reason_for_call)
{
case DLL_PROCESS_ATTACH:
case DLL_THREAD_ATTACH:
case DLL_THREAD_DETACH:
case DLL_PROCESS_DETACH:
break;
}
return TRUE;
}

MYPUTS_API void myPuts(LPTSTR lpszMsg)
{
DWORD cchWritten;
HANDLE hStdout;

// Get a handle to the standard output device.

hStdout = GetStdHandle(STD_OUTPUT_HANDLE);

// Write a null-terminated string to the standard output device.

while (*lpszMsg)
WriteFile(hStdout, lpszMsg++, 1, &cchWritten, NULL);
}

[akiko]

MYPUTS_API前加上extern "C"

[zhutoucoding]

通过了，谢谢！

不过还不能给分，你要说说为什么 :)

[neptunez]

Because of the difference of naming scheme between c and c++ compiler.

Another way to solve this problem is to try to compile it using c compiler while not c++ one, which is VC's default.

[zhutoucoding]

Another question:

A dll can bu load at ether loadtime or runtime. The sample of runtime mentioned above have passed successfully, but the sample of loadtime is false. The following is the test code:

------------------------------------------------------------------------------
#include <windows.h>
#include "myputs.h"

VOID main(VOID)
{
myPuts("message printed using the DLL function\n");
}
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can you tell me why it can not compile successfully. ThanX