Kenwood HP 9000 manual Shlfindsym Example

Shared Library Management Routines

The shl_load Shared Library Management Routines

1.declare a pointer to a data structure of the same type as the data structure to access in the library

2.using shl_findsym with the type parameter set to TYPE_DATA, find the symbol in the shared library and assign its address to the pointer declared in Step 1

3.access the data through the pointer obtained in Step 2

shl_findsym Example

Suppose you have a set of libraries that output to various graphics devices. Each graphics device has its own library. Although the actual code in each library varies, the routines in these shared libraries have the same name and parameters, and the global data is the same. For instance, they all have these routines and data:

gopen()	opens the graphics device for output
gclose()	closes the graphics device
move2d(x,y) moves to pixel location x,y
draw2d(x,y) draws to pixel location x,y from current x,y
maxX	contains the maximum X pixel location on the output
	device
maxY	contains the maximum Y pixel location on the output
	device

The following example shows a C program that can load any supported graphics library at run time, and call the routines and access data in the library. The program calls load_lib (see “load_lib — Function to Load a Shared Library”) to load the library.

Load a Shared Library and Call Its Routines and Access Its Data

#include <stdio.h>	/* contains standard I/O defs			*/
#include <stdlib.h>	/*	contains getenv	definition	*/
#include <dl.h>	/*	contains shared	library type defs */
/*

*Define linker symbols:

*/

#define GOPEN	“gopen”
#define GCLOSE	“gclose”
#define MOVE2D	“move2d”
#define DRAW2D	“draw2d”
#define MAXX	“maxX”
#define MAXY	“maxY”

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