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Listing 3: DELAYIMP.H
Delay-loading support and hook functions

/* DELAYIMP.H   - delay-loading support and hook functions */

#pragma once
#if !defined __DELAYIMP_H
#define __DELAYIMP_H

#if defined __cplusplus
  extern "C" {
#endif

/* The ImgDelayDescr structure defines the raw format of internal tables
 * that the linker generates for each delay-loaded DLL.
 */
typedef const struct ImgDelayDescr *PCImgDelayDescr;

typedef struct DelayLoadProc {
  BOOL       fImportByName;
  union {
      LPCSTR szProcName;
      DWORD  dwOrdinal;
  };
} DelayLoadProc;

typedef struct DelayLoadInfo {
  DWORD           cb;           /* size of the structure */
  PCImgDelayDescr pidd;         /* raw form of the data */
  FARPROC       * ppfn;         /* points to address of function to import */
  LPCSTR          szDll;        /* filename of the DLL */
  DelayLoadProc   dlp;          /* name or ordinal of function to import */
  HMODULE         hmodCur;      /* module handle of the DLL after loading it */
  FARPROC         pfnCur;       /* address of imported function */
  DWORD           dwLastError;  /* error received (in an error notification) */
} DelayLoadInfo, * PDelayLoadInfo;

typedef FARPROC (WINAPI *PfnDliHook)(unsigned dliNotify, PDelayLoadInfo pdli);


/* Unload support: unload a specific delay-loaded DLL or unload all
 * delay-loaded DLLs by setting "szDll" to NULL.
 */
BOOL WINAPI __FUnloadDelayLoadedDLL(LPCSTR szDll);

/* Structured Exception Handling information */
#if !defined ERROR_MOD_NOT_FOUND
  #define ERROR_MOD_NOT_FOUND   126L    /* from WINERROR.H */
#endif
#if !defined ERROR_PROC_NOT_FOUND
  #define ERROR_PROC_NOT_FOUND  127L    /* from WINERROR.H */
#endif
#if defined __BORLANDC__
  #define FACILITY_DELAYLOAD    251L
#else /* Microsoft Visual C/C++ */
  #define FACILITY_DELAYLOAD    109L
#endif
#define VcppException(sev,err)  ((sev) | (FACILITY_DELAYLOAD<<16) | err)

/* Delay-load notification and failure hooks
 *
 * The "notification hook" function is called for every function to import
 * (but only once per function). The dliNotePreLoadLibrary notification is
 * only sent if the DLL is not already loaded. The "failure hook" function
 * gets called if a LoadLibrary() or GetProcAddress() fails. The failure
 * hook may then try to fix the situation and return the requested handle
 * or address.
 *
 * __pfnDliNotifyHook receives:
 *   dliStartProcessing
 *   dliNotePreLoadLibrary
 *   dliNotePreGetProcAddress
 *   dliNoteEndProcessing
 *
 * __pfnDliFailureHook receives:
 *   dliFailLoadLib
 *   dliFailGetProc
 */
#if defined __BORLANDC__
  /* C++ Builder 5 contains the hook variables in both a static link library
   * and a DLL RTL.
   */
  #define DeclSpec      __declspec(dllimport)
#else
  /* Microsoft Visual C/C++ has only a static linked lib for delay-loading */
  #define DeclSpec
#endif

enum {
  dliStartProcessing,       /* start import of function; may return FARPROC */
  dliNotePreLoadLibrary,    /* pre-LoadLibrary; may return HMODULE */
  dliNotePreGetProcAddress, /* pre-GetProcAddress; may return FARPROC */
  dliFailLoadLib,           /* LoadLibrary-failure; may return HMODULE */
  dliFailGetProc,           /* GetProcAddress-failure; may return FARPROC */
  dliNoteEndProcessing,     /* done importing a function */
};

DeclSpec extern
PfnDliHook   __pfnDliNotifyHook;
DeclSpec extern
PfnDliHook   __pfnDliFailureHook;

#undef DeclSpec


#if defined __cplusplus
  } /* extern "C" */
#endif

#endif  /* !defined __DELAYIMP_H */

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