Dynamic Loader Library (DL library)
**Version: 0.02**

0. Introduction

DL library is a very very simple library of Dynamic Loading implemented for POSIX and Windows Platforms, This
library offers a simple abstraction layer beetween LoadLibrary and dl**() functions. This is intended to 
simplify the process of loading libraries at runtime, which is very useful in many programs where dynamic 
linking from the linker is not a major advantage.

1. Copyright, license, etc...

Copyright (C) 2025 - Andres26 

This program is free software; you can redistribute it and/or modify it under the terms of the MIT license.

See './COPYING' file for more info.

2. Dependencies

The code has no important dependencies, but this requires Windows API or dl functions in POSIX.

3. Contents of this project

	* dl.h: Contains the main interface of the library, dl_mod is used for initialize library, load module and
	its symbols. 'file' is the file from which the module is located for later loading by the library, 'state'
	is the flag returned when the module is loaded, and 'handle' is the pointer used by host library for load 
	modules.
	
	Types of the library:
	
	dl_func_ptr as void* -> refers to the function pointer.

	dl_handle_ptr as void* -> refers to the host library handle pointer.
	
	'dl.h' has several functions which are similar to the POSIX environment.
	
	int dl_open_module(struct dl_mod *mod, const char *file, int)
	
		Open module from file. First detect if 'mod' is a valid pointer, and load module with host functions.
		
		Returns: 1 in case of fail, 0 on success and -1 if the 'dl' pointer is NULL.
		
		NOTE: To ensure compatibility with Windows and POSIX systems, the third parameter which belongs to the 
		library loading mode, is not used. 
	
	dl_func_ptr dl_sym_module(struct dl_mod* mod, const char *symbol)
	
		Return the pointer of a function in the module, 'symbol' is the name of the function/variable to call
		from main program.
	
	int dl_close_module(dl_handle_ptr handle)
	
		Close the opened module.
		
	const char *dl_get_error();
	
		Return string if the library fails.
		
	
	* dl.c: Contains the source of prototypes of 'dl.h'
	
		NOTE: For loading symbol RTDL_LAZY is used as default in POSIX systems.
		
4. Contact

Any questions, doubts or clarifications, mail to:

	andrescamorao9@gmail.com

For bug tracking, please write to:

	https://github.com/Andres2626/DL-Library/issues
	
5. Appendix A: Minimal example of use

/* main.c -> main program */

/* include library header file */
#include "dl.h"

/* type to function pointer */
typedef void (*func)();

int main(int argc, char **argv)
{
	struct dl_t mod; /* create library structure */
	
	/* open module */
	if (!dl_open_module(&mod, "./main.mod", 0)) {
		fprintf(stderr, "Error loading main.mod: %s\n", dl_get_error()); /* error */
		return 1;
	}
	
	/* load arbitrary module function */
	func module_main = (func)dl_sym_module(&mod, "module_main");
	if (!module_main) {
		fprintf(stderr, "module_main() not found: %s\n", dl_get_error()); /* error */
		dl_close_module(&mod);  /* close the module in case of error */
		return 1;
	}
	
	/* call to module function loaded */
	module_main();
	
	/* close library */
	dl_close_module(&mod);
	
	return 0;
}

/* module_main.c -> module functions */

#include <stdio.h> /* printf function */

/* 
* '_EXPORT_DL' definition depends on the host compiler. On Windows compilers, __declspec(dllexport) 
* is used to export a function, whereas on POSIX systems, __attribute__((visibility("default"))) 
* is used. However, this is not universal across all platforms, so check carefully before exporting 
* a function, as the library should, and only should, detect that the function was exported for 
* DL; otherwise, the function will not be called and the library will generate an error.
*/
#if defined(_WIN32) && !defined(__CYGWIN__)
/* 
 * CYGWIN system are considered POSIX environment, for this reason the usual definition for 
 * exporting symbols as is the case with pure _WIN32 systems (mingw32, VS, ...) is not used. 
 */
#define _EXPORT_DL __declspec(dllexport)
#else
#define _EXPORT_DL __attribute__((visibility("default"))) /* FIXME: Not guaranteed on all compilers */
#endif

/* function exported to DL */
_EXPORT_DL void module_main() 
{
	/* print welcome message */
	printf("Hello World from my module!\n");
}
	
Andres26
14-04-2025
github.com/Andres2626/DL-Library