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在Linux创建库函数(8)

王朝system·作者佚名  2008-05-19
窄屏简体版  字體: |||超大  

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。

 
 
 
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