asked on

dynamic linking

Can somebody please explain to me how to use a dynamic link library, using C. This code I have just got from exsamles in my helpfiles, it does not work very well! :o) I am aware of the concept of dynamic linking...but the practical part hmm..
How would the following be done? Calling a function in a .dll displaying a message sent by a calling application?

#include <windows.h>

VOID myPuts(LPTSTR);

void main(){

char dllName[] = "test";
HINSTANCE myInstance;
FARPROC myProc;

myInstance = LoadLibrary( dllName );
myProc = GetProcAddress( myInstance, "myPuts" );

myProc("message printed using the DLL function\n");
getch();
}

#include <windows.h>

VOID _export 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);

}

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basant

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sa9813

ASKER

Thank you for your time! I need some time to evaluate this...I have tried to put together a .def-file, it complains about the @ in

Exports
myPuts @1

I have imported it to the .dll project, but it does'nt work...this is what I've got

#include <windows.h>
#include <conio.h>

//is this correct?
typedef void( *myFuncType )( float f );

void main(){

char dllName[] = "test";
HINSTANCE myInstance;
FARPROC myProc;

myInstance = LoadLibrary( dllName );

if( myInstance == 0 )
printf( "fel" );

myProc = ( myFuncType ) GetProcAddress( myInstance, "myPuts" );
myProc( 1.0 );
getch();
}

#include <windows.h>
#include "test.def"

int myPuts( float f )
{
//just return something
return ( 5 );
}

basant

(1) Have u tried dumpbin.exe utility.
Show me the output of
dumpbin /exports one.dll

(2) R u be able to load library successfully.
if( myInstance == 0 )
printf( "fel" );

(3) Check whether your GetProcAddress
is Successful or failing.

myProc = ( myFuncType )GetProcAddress( myInstance, "myPuts" );
if( myProc == 0)
{
printf("\n Error :");
return;
}

(4) Is your DLL function in C++.
If yes then
use extern "C" for declartion of function.

sa9813

ASKER

I have not got it up working yet, but I now know what it should look like, I think I can do the rest with the helpfile. Thanx.

basant

Any thing more if u want I can provide the help.

sa9813

ASKER

Okey, basant I will study this information now, learn how it's suppose to work! I will ask you if I there is something I do not understand. I do not have dumpin.exe, maybe this is provided by microsoft, I'm using borland C++? I found a program ( provided by borland )that created a .def file, provided the .dll, compiler complained about it though! Strange!

basant

This is not dumpin.exe
this is dumpbin.exe

This shipped with VC look for the directory
C:\Program Files\Microsoft Visual Studio\VC98\Bin :

Note go to bin directory where VC is installed.