This article describes how to link an OPENSTEP Enterprise 4.2 application against a third-party C library; in this case, the Lightweight Directory Access Protocol (LDAP) library from Netscape.

On Windows NT, shared libraries are stored as dynamically loaded libraries (.DLL) files. To link against a third-party DLL, you also need the associated .LIB file. The .LIB file contains the actual entry point relocations into the DLL. Compiling and linking requires only the header (.h) and .LIB files. At run time, install the .DLL in a directory that appears in your system's PATH environment variable.

The necessary third party files to link against the LDAP library can be downloaded from Netscape at http://devedge.netscape.com/one/directory/ . For this example we downloaded dk11e32.exe, which is a self-extracting file. The LDAP files were installed in the following locations:

• nsldap32v11.lib in c:/OpenStep/Lib
• ldap.h in c:/OpenStep/include (as well as the other LDAP headers)
• nsldap32v11.dll in c:/Next/NextLibrary/Executables

• PATH should include c:/NextLibrayr/Executables
• INCLUDE should include c:/OpenStep/include

Below is source code from a simple test app. This application will display its version number (110) in a text field when a button is pressed. Note that for this simple test case, no attempt was made to configure an LDAP Directory server.

//========= AppControl.h =========================================

#import <AppKit/Appkit.h>
#define LDAP_API(rt) rt          // <== this did the trick in the test app!
#import <ldap.h>

@interface AppControl : NSObject
{
id pTextField01;                                  //<==== pointer to text field
}

- (void)clickedCallLDAP:(id)sender;  //<=== action method - called when
//
button is clicked

@end

//==============================================================

Notice that b efore importing the Netscape  ldap.h  file  in AppControl.h above,
the following define occurs:

#define LDAP_API(rt) rt

Without this line LDAP_API will get set this way (in ldap.h):

#define LDAP_API(rt) __declspec( dllexport ) rt

This definition will generate wrong linker symbols that will not be
found in the library. The result is linker errors (error LNK2001: unresolved
external symbol ....). Below is the implementation file.

//============ AppControl.m ======================================

#import "AppControl.h"

@implementation AppControl

- (void)clickedCallLDAP:(id)sender
{
LDAPVersion ver;
double SDKVersion;

SDKVersion = ldap_version( &ver );              //<=== get version number

printf("LDAP version = %7.3f\n", SDKVersion);
[pTextField01 setIntValue:SDKVersion];        //<=== display in text field
}

@end

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