和luster学习在Linux创建库函数（8） （完）

/* libhello.c - demonstrate library use. */
#include 
void hello(void)
{
  printf("Hello, library world.
");
}

/* libhello.h - demonstrate library use. */
void hello(void);

/* demo_use.c -- demonstrate direct use of the "hello" routine */
#include "libhello.h"
int main(void) 
{
 hello();
 return 0;
}

#!/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

#!/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

/* 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;
}