Initializing +a Library

Export +functions for initializing and closing the library

The library +can export more than one function for initializing and closing the library.

The +client of the library calls the initialization function before requesting +any services and calls close when the client does not use the library.

Example:

There +is a DLL called xxx.dll. Two functions InitXXX() and CloseXXX() are +exported from this DLL. The library code can look like the following:

Library +header file xxx_init.h:

.... +IMPORT_C void InitXXX(); +IMPORT_C CloseXXX(); +.... +

Library source file xxx_init.cpp:

static int _InitCount = 0; +EXPORT_C void InitXXX() +{ + if(_InitCount++ <= 0) + { + // initialize xxx.dll + } +} +EXPORT_C CloseXXX() +{ + if(--_InitCount <= 0) + { + // free all the resources + } +} +

User code looks like the following:

#include <xxx_init.h> +... +int main() +{ + InitXXX(); + .... + .... + CloseXXX(); + return 0; +} +

Exported functions +check whether the library is initialized

Every exported function +can check whether the library has been initialized. The library can export +one function (for example, CloseLib()) and this can be called +before exiting main().

Example:

Library +header file xxx.h:

.... +IMPORT_C void X_Export_Api1(); +IMPORT_C void X_Export_Api2(); +.... +

Library source file xxx.cpp:

static int _InitCount = 0; +#define INIT_LIB if(_InitCount == 0) \ + {\ + _InitCount++; \ + InitXXX(); \ + } +LOCAL_C void InitXXX() +{ + // initialize xxx.dll +} +LOCAL_C CloseXXX() +{ + // free all the resources +} +EXPORT_C void X_Export_Api1() +{ + INIT_LIB; + ... + ... +} +

User code looks like the following:

#include <xxx.h> +... +int main() +{ + .... + .... + X_Export_Api1(); + .... + .... + X_Export_Api2(); + .... + .... + return 0; +} +

Library defines +a static object

The library can define static objects and call the +initialization code from the constructor of these static objects so that before +calling, the application entry point library will be initialized.

Example:

Library +header file xxx.h:

.... +IMPORT_C void X_Export_Api1(); +IMPORT_C void X_Export_Api2(); +....

Library source file xxx.cpp:

LOCAL_C void InitXXX() +{ + // initialize xxx.dll +} +LOCAL_C CloseXXX() +{ + // free all the resources +} +class LibInit +{ + LibInit(); + ~LibInit(); +}; +LibInit::LibInit() +{ + // put all library initialization code here. + InitXXX(); +} +LibInit::~LibInit() +{ + // free all resources + CloseXXX(); +} +static LibInit _libInit; +

User code looks like the following:

#include <xxx.h> +int main() +{ + .... + .... + X_Export_Api1(); + .... + .... + X_Export_Api2(); + .... + .... + return 0; +} +