摘要:下面是一些例子，例子中我们会使用三种函数库（静态的、共享的和动态加载的函数库）。文件libhello.c是一个函数库，libhello.h是它的头文件；demo_use.c则是一个使用了libhello函数库的。Script_static和script_dynamic分别演示如何以静态和共享方式使用函数库，而后面的demo_dynamic.c和script_dynamic则表示演示如何以动态加载函数库的方式来使用它。

　　6. 更多的例子

　　下面是一些例子，例子中我们会使用三种函数库（静态的、共享的和动态加载的函数库）。文件libhello.c是一个函数库，libhello.h是它的头文件；demo_use.c则是一个使用了libhello函数库的。Script_static和script_dynamic分别演示如何以静态和共享方式使用函数库，而后面的demo_dynamic.c和script_dynamic则表示演示如何以动态加载函数库的方式来使用它。

　　6.1. File libhello.c

　　/* libhello.c - demonstrate library use. */

　　#include

　　void hello(void)

　　{

　　printf("Hello, library world.

　　");

　　}

　　6.2. File libhello.h

　　/* libhello.h - demonstrate library use. */

　　void hello(void);

　　6.3. File demo_use.c

　　/* demo_use.c -- demonstrate direct use of the "hello" routine */

　　#include "libhello.h"

　　int main(void)

　　{

　　hello();

　　return 0;

　　}

　　6.4. File script_static

　　#!/bin/sh

　　# Static library demo

　　# Create static library's object file, libhello-static.o.

　　# I'm using the name libhello-static to clearly

　　# differentiate the static library from the

　　# dynamic library examples, but you don't need to use

　　# "-static" in the names of your

　　# object files or static libraries.gcc -Wall -g -c -o libhello-static.o

　　libhello.c

　　# Create static library.ar rcs libhello-static.a libhello-static.o

　　# At this point we could just copy libhello-static.a

　　# somewhere else to use it.

　　# For demo purposes, we'll just keep the library

　　# in the current directory.

　　# Compile demo_use program file.gcc -Wall -g -c demo_use.c -o demo_use.o

　　# Create demo_use program; -L. causes "." to be searched during

　　# creation of the program. Note that this command causes

　　# the relevant object file in libhello-static.a to be

　　# incorporated into file demo_use_static.gcc -g -o demo_use_static

　　demo_use.o -L. -lhello-static

　　# Execute the program../demo_use_static

　　6.5. File script_shared

　　#!/bin/sh

　　# Shared library demo

　　# Create shared library's object file, libhello.o.gcc -fPIC -Wall

　　-g -c libhello.c

　　# Create shared library.

　　# Use -lc to link it against C library, since libhello

　　# depends on the C library.gcc -g -shared -Wl,-soname,libhello.so.0 -o

　　libhello.so.0.0 libhello.o -lc# At this point we could just copy

　　libhello.so.0.0 into

　　# some directory, say /usr/local/lib.

　　# Now we need to call ldconfig to fix up the symbolic links.

　　# Set up the soname. We could just execute:

　　# ln -sf libhello.so.0.0 libhello.so.0

　　# but let's let ldconfig figure it out./sbin/ldconfig -n .

　　# Set up the linker name.

　　# In a more sophisticated setting, we'd need to make

　　# sure that if there was an existing linker name,

　　# and if so, check if it should stay or not.ln -sf libhello.so.0

　　libhello.so

　　# Compile demo_use program file.gcc -Wall -g -c demo_use.c -o

　　demo_use.o

　　# Create program demo_use.

　　# The -L. causes "." to be searched during creation

　　# of the program; note that this does NOT mean that "."

　　# will be searched when the program is executed.gcc -g -o demo_use

　　demo_use.o -L. -lhello

　　# Execute the program. Note that we need to tell the program

　　# where the shared library is,

　　using LD_LIBRARY_PATH.LD_LIBRARY_PATH="." ./demo_use

　　6.6. File demo_dynamic.c

　　/* demo_dynamic.c -- demonstrate dynamic loading and

　　use of the "hello" routine */

　　/* Need dlfcn.h for the routines to

　　dynamically load libraries */

　　#include

　　#include

　　#include

　　/* Note that we don't have to include "libhello.h".

　　However, we do need to specify something related;

　　we need to specify a type that will hold the value

　　we're going to get from dlsym(). */

　　/* The type "simple_demo_function" describes a function that

　　takes no arguments, and returns no value: */

　　typedef void (*simple_demo_function)(void);

　　int main(void)

　　{

　　const char *error;

　　void *module;

　　simple_demo_function demo_function;

　　/* Load dynamically loaded library */

　　module = dlopen("libhello.so", RTLD_LAZY);

　　if (!module)

　　{

　　fprintf(stderr, "Couldn't open libhello.so: %s

　　",dlerror());

　　exit(1);

　　}

　　/* Get symbol */

　　dlerror();

　　demo_function = dlsym(module, "hello");

　　if ((error = dlerror()))

　　{

　　fprintf(stderr, "Couldn't find hello: %s

　　", error);

　　exit(1);

　　}

　　/* Now call the function in the DL library */

　　(*demo_function)();

　　/* All done, close things cleanly */

　　dlclose(module);

　　return 0;

　　}

　　6.7. File script_dynamic

　　#!/bin/sh

　　# Dynamically loaded library demo

　　# Presume that libhello.so and friends have

　　# been created (see dynamic example).

　　# Compile demo_dynamic program file into an object file.gcc

　　-Wall -g -c demo_dynamic.c

　　# Create program demo_use.

　　# Note that we don't have to tell it where to search

　　for DL libraries,

　　# since the only special library this program uses won't be

　　# loaded until after the program starts up.

　　# However, we DO need the option -ldl to include the library

　　# that loads the DL libraries.gcc -g -o demo_dynamic

　　demo_dynamic.o -ldl

　　# Execute the program. Note that we need to tell the

　　# program where get the dynamically loaded library,

　　# using LD_LIBRARY_PATH.LD_LIBRARY_PATH="." ./demo_dynamic

　　by luster(luster@linuxaid.com.cn,hwang@ustc.edu)

　　2001-8-22

　　（完）

　　任何bug发信给我，一起修改。先谢谢。