源文件（这是Rechard Steven在unix 高级编程的代码）
# cat liberr.h
#ifndef _LIBERR_H
#define _LIBERR_H
#include <stdarg.h>
#define MAXLINELEN 4096
void err_ret(const char *fmt, ...);
void err_quit(const char *fmt, ...);
void log_ret (char *logfile,const char *fmt, ...);
void log_quit(char *logfile,const char *fmt, ...);
void err_prn(const char *fmt,va_list ap, char *logfile);
#endif
# cat liberr.c
#include <errno.h>
#include <stdarg.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include "liberr.h"
void err_ret(const char *fmt, ...)
{
va_list ap;
va_start(ap,fmt);
err_prn(fmt,ap,NULL);
va_end(ap);
return;
}
void err_quit(const char *fmt, ...)
{
va_list ap;
va_start(ap, fmt);
err_prn(fmt, ap, NULL);
va_end(ap);
exit(EXIT_FAILURE);
}
void log_ret(char *logfile,const char *fmt, ...)
{
va_list ap;
va_start(ap,fmt);
err_prn(fmt,ap,logfile);
va_end(ap);
return;
}
void log_quit(char * logfile,const char *fmt, ...)
{
va_list ap;
va_start(ap,fmt);
err_prn(fmt,ap,logfile);
va_end(ap);
exit(EXIT_FAILURE);
}
extern void err_prn(const char *fmt, va_list ap, char *logfile)
{
int save_err;
char buf[MAXLINELEN];
FILE *plf;
save_err=errno;
vsprintf(buf,fmt,ap);
sprintf(buf + strlen(buf),":%s",strerror(save_err));
strcat(buf,"\n");
fflush(stdout);
if(logfile != NULL)
if((plf = fopen(logfile,"a")) != NULL ) {
fputs(buf,plf);
fclose(plf);
} else
fputs("failed to open log file\n,", stderr);
else
fputs(buf,stderr);
fflush(NULL);
return;
}
编译及打包静态包
#gcc -c liberr.c -o liberr.o
#ar rcs liberr.a liberr.o
# cat errtest.c
#include <stdio.h>
#include <stdlib.h>
#include "liberr.h"
#define ERR_QUIT_SKIP 1
#define LOG_QUIT_SKIP 1
int main(void)
{
FILE *pf;
puts("Tesing err_ret");
if((pf = fopen("foo","r")) == NULL) {
err_ret("%s %s","err_ret:","failed to open foo");
}
puts("Tesing log_ret");
if((pf = open("foo","r")) == NULL) {
log_ret("errtest.log","%s %s","log_ret:","failed to open foo");
}
#ifndef ERR_QUIT_SKIP
puts("Testing err_quit");
if((pf = open("foo","r")) == NULL) {
err_ret("%s %s","err_ret:","failed to open foo");
}
#endif
#ifndef LOG_QUIT_SKIP
puts("Testing log_quit");
if((pf = open("foo","r")) == NULL) {
log_ret("errtest.log","%s %s","log_quit:","failed to open foo");
}
#endif
exit(EXIT_SUCCESS);
}
静态库编译：
[root@pc201 linux_guide]# gcc errtest.c -o errtest -L. -lerr --static
errtest.c: In function ‘main’:
errtest.c:18: warning: assignment makes pointer from integer without a cast
/usr/bin/ld: cannot find -lc
collect2: ld returned 1 exit status
解决办法是安装glibc-static
[root@pc201 linux_guide]# yum install glibc-static
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* base: mirrors.163.com
* extras: mirrors.163.com
* updates: ftp.stu.edu.tw
Setting up Install Process
Resolving Dependencies
--> Running transaction check
.... ..... ..........
Complete!
再次运行就没有报错了
[root@pc201 linux_guide]# gcc errtest.c -o errtest -L. -lerr --static
errtest.c: In function ‘main’:
errtest.c:18: warning: assignment makes pointer from integer without a cast
与动态库分析：
建立动态库：
#gcc -fPIC -g -c liberr.c -o liberr.o
#gcc -g -shared -Wl,soname,liberr.so -o liberr.so.1.0.0 liberr.o -lc
动态链接编译的结果
静态编译的结果
看到比动态链接的大接近100倍。
下面示例调用动态库内部的函数。这里，我们要调用liberr.so里的err_ret函数：
# cat dltest.c
#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>
int main(void)
{
void *handle;
void (*errfcn) (const char *fmt, ...); //errfcn是函数指针，它要指向要调用的err_ret
const char *errmsg;
FILE *pf;
handle = dlopen("./liberr.so",RTLD_NOW); // dlopen打开liberr.so，返回handle
if(handle==NULL) {
fprintf(stderr,"Failed to load liberr.so:%s\n",dlerror());
exit(EXIT_FAILURE);
}
dlerror(); // reset dl error
errfcn=dlsym(handle,"err_ret"); // dlsym 寻找handle里的err_ret函数
if((errmsg = dlerror()) != NULL) {
fprintf(stderr,"Didn't find err_ret:%s\n",errmsg);
exit(EXIT_FAILURE);
}