/** @file ../include/dlfcn.h

@internalComponent

*/

/** @fn  dlopen(const char *filename, int flag)

@param filename

@param flag

Note: This description also covers the following functions -

 dlsym()  dlerror()  dlclose() 

@code

 RTLD_LAZY In the current implementation this flag causes the external function names to be resolved

 prior to returning from dlopen.

 RTLD_NOW In the current implementation this flag causes the external function names to be resolved

 prior to returning from dlopen.

@endcode

@code

 RTLD_GLOBAL Symbols exported from this shared library object will not be available

 for the processing of relocation addresses of any other shared library object.

 RTLD_LOCAL Symbols exported from this shared library object will not be available

 for the processing of relocation of addresses in any other shared library object.

@endcode

  These functions provide interfaces to the services of the Symbian Loader 

Server. Operations are provided to load dynamic link libraries (DLLs) into the 

current process's address space, to obtain the address bindings of symbols 

exported by the DLLs, and to remove the DLLs from the process's address space 

when they are no longer required.

 The dlopen function loads the DLL specified in the filename argument and returns a descriptor if successful. The descriptor 

  returned can be used for later references to the DLL within the calls to dlsym and dlclose. The user side code should not attempt to modify or interpret 

  the value of the descriptor returned by dlopen.

 If the DLL specified by the filename argument is not in the address space prior to the call to dlopen, it is loaded into the address space. When the DLL is first 

  loaded into the address space constructors of the DLL's global objects 

  are invoked. If the DLL specified by the filename argument has already been placed in the process's address 

  space in a previous call to dlopen, invoking dlopen on the same DLL does not add it a second time, instead the 

  reference count of dlopen operations on that DLL is incremented. Invoking dlclose on the DLL handle decrements the reference count associated 

  with the DLL. When this reference count reaches zero, the DLL is unloaded from 

  the process address space. dlopen returns NULL if path argument is NULL.

 The mode parameter determines the type of operation performed by dlopen with respect to the symbol address relocations and the visibility 

  of the symbols to other shared libraries loaded by the process. The mode argument has the same effect regardless of its value: It is to 

  resolve all the external function references immediately within dlopen. This is because the external function references are bound 

  immediately by dlopen. For all practical purposes, therefore, the mode parameter's value is assumed to be RTLD_NOW ORed with RTLD_LOCAL. 

  Once a DLL is loaded into the address space, all the symbols exported by it 

  can only be accessed by specifying the handle associated with the DLL. The behaviour 

  is outlined below.

 mode must contain one of the following values, possibly ORed with additional 

  flags described below: RTLD_LAZY In the current implementation this flag causes the external function names to be resolved

prior to returning from dlopen. RTLD_NOW In the current implementation this flag causes the external function names to be resolved

prior to returning from dlopen.

 One of the following flags may be ORed into the mode argument: RTLD_GLOBAL Symbols exported from this shared library object will not be available

for the processing of relocation addresses of any other shared library object. RTLD_LOCAL Symbols exported from this shared library object will not be available

for the processing of relocation of addresses in any other shared library object.

 If path argument contains a slash character the entire argument is used 

  as the pathname for the file. C: is considered to be the root and C:\\ is prefixed 

  to the path argument to locate the shared library object. If path contains just the name of the shared library to be loaded, the 

  default location is sys\\bin. The string in the path argument is limited to a maximum of 256 characters.

 dlopen returns the handle for the dynamic library loaded into the address space

of the current process.

 dlsym function returns the address binding of the symbol associated 

  with the ordinal number. The NULL-terminated character string symbol contains the ordinal number (address lookup is based on ordinal 

  number). The symbols exported by shared DLLs added to the address space by dlopen can be accessed only through calls to dlsym.

 Symbol names per se are not searched. Instead dlsym locates the ordinal number corresponding to a symbol name and 

  returns the address of the memory location where the symbol is loaded. Ordinal 

  numbers therefore form the basis of the name lookup. Since all handles have 

  to be identified explicitly (that is, as returned by dlopen ), dlsym returns NULL when presented with special handles such as RTLD_NEXT, 

  RTLD_SELF and RTLD_DEFAULT. The implementation treats a NULL handle passed to dlsym as an error and returns NULL.

 The dlsym function returns a null pointer if the symbol (ordinal) cannot 

  be found and sets an error condition which may be queried with dlerror.

 The dlerror function

returns a null-terminated character string describing the last error that

occurred during a call to dlopen, dlsym,

or dlclose.

If no such error has occurred, dlerror returns a null pointer.

At each call to dlerror,

the error indication is reset.

Thus in the case of two calls

to dlerror,

where the second call follows the first immediately, the second call

will always return a null pointer.

 The dlclose function deletes a reference to the DLL referenced by handle. If the reference count drops to 0, the DLL is removed from the 

  address space and handle is rendered invalid. Just before removing the DLL from the current 

  process's address space the destructors of the DLL's global objects 

  are invoked. If dlclose is successful it returns 0. Otherwise it returns -1 and sets 

  an error condition that can be interrogated with dlerror.

Notes:

 The ordinal numbers associated with the functions in a DLL are in the DLL's 

.def file.

@publishedAll

@externallyDefinedApi

*/

/** @fn  dlsym(void *  handle, const char *  symbol)

@param handle

@param symbol

Refer to  dlopen() for the documentation

@publishedAll

@externallyDefinedApi

*/

/** @fn  dlerror(void)

Refer to  dlopen() for the documentation

@publishedAll

@externallyDefinedApi

*/

/** @fn  dlclose(void *handle)

@param handle

Refer to  dlopen() for the documentation

@publishedAll

@externallyDefinedApi

*/

/** @def RTLD_LAZY

Modes and flags for dlopen(). Bind function calls lazily. 

@publishedAll

@externallyDefinedApi

*/

/** @def RTLD_NOW

Modes and flags for dlopen(). Bind function calls immediately. 

@publishedAll

@externallyDefinedApi

*/

/** @def RTLD_GLOBAL

Modes and flags for dlopen(). Make symbols globally available.

@publishedAll

@externallyDefinedApi

*/

/** @def RTLD_LOCAL	

Modes and flags for dlopen(). Opposite of RTLD_GLOBAL, and the default. 

@publishedAll

@externallyDefinedApi

*/

/** @def RTLD_NEXT	

Special handle arguments for dlsym()/dlinfo(). Search subsequent objects.

@publishedAll

@released

*/

/** @def RTLD_DEFAULT	

Special handle arguments for dlsym()/dlinfo(). Use default search algorithm.

@publishedAll

@released

*/

/** @def RTLD_SELF	

Special handle arguments for dlsym()/dlinfo(). Search the caller itself.

@publishedAll

@released

*/