打印pid，写着玩。

 #include <stdio.h>
 #include <string.h>
 #include <dirent.h>
 #include <limits.h>
 #include <unistd.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <fcntl.h>

 #define PROC "/proc/"

 typedef int Myfunc(int pid) ;
 static Myfunc  myfunc;

 #define P()     printf("%s:%d\n",__FUNCTION__,__LINE__)
 static int dopath(Myfunc *func);

 int main(int argc,char *argv[])
 {
     return dopath(myfunc);
 }
 static int
 dopath(Myfunc *func)
 {
     //struct stat         statbuf;
     struct dirent        *dirp;
     DIR                    *dp;
     int                 ret;
     char                *ptr;

     //if()
     if((dp = opendir(PROC)) == NULL)
     {
         perror("open");
         return -;
     }

     while((dirp = readdir(dp)) != NULL)
     {
         if(strcmp(dirp->d_name,".") ==  ||strcmp(dirp->d_name,"..")==)
         {
             continue;
         }
         int pid = atoi(dirp->d_name);
         //printf("pid =%d\n",pid);
         if(pid == )
         {
             continue;
         }
         int ret = myfunc(pid);
         if(ret != )
         {
             printf("parse error!\n");
             return -;
         }
     }
     if(closedir(dp) < )
     {
         printf("cant't close directory /proc");
         return -;
     }
     return ;
 }
 static int
 myfunc(int pid)
 {
     char path[]={};
     const char *name="Name:";
     const char *state = "State:";
     char pname[] = {};

     sprintf(path,"/proc/%d/status",pid);
     if(access(path,F_OK)!=)
     {
         printf("%s not exist.\n",path);
         return -;
     }

     int fd = open(path,O_RDONLY);
     if(fd<)
     {
         perror("open");
         return -;
     }

     char buf[]={};
     int length = read(fd,buf,sizeof(buf));
     if(length<)
     {
         perror("read");
         close(fd);
         return -;
     }
     char *p0 =strstr(buf,name);
     char *p1 =strstr(buf,state);
     memcpy(pname,p0+strlen(name)+,p1-p0-strlen(name)-);
     printf("pname:%s\n",pname);

     close(fd);

     return ;
 }

写几行代码来打印pid对应的进程名。

java版本：

 import java.io.BufferedReader;
 import java.io.File;
 import java.io.FileInputStream;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStreamReader;
 import java.io.Reader;

 /**
  * @author jevan (jevan.cnblogs.com)
  * @version 1.0 at 2013-11-27
  *
  */
 public class PrintPID {

     /**
      * @param args
      */
     public static void main(String[] args) {
         printPid();
     }

     private static void printPid()
     {

         File proc = new File("/proc");
         for(File f:proc.listFiles())
         {
             if(f.getName().equals(".")||f.getName().equals(".."))
                 continue;

             if(f.isDirectory())
             {
                 int pid = toInt(f.getName());
                 if(pid == 0)
                     continue;

                 File fname = new File("/proc/"+f.getName()+"/status");

                 if(!fname.exists())
                     continue;

                 String line0 =read0Line("/proc/"+f.getName()+"/status");

                 String[] tmp = line0.split(":",2);
                 if(tmp==null||tmp.length!=2)
                 {
                     continue;
                 }
                 p("==>"+tmp[1]);

             }
         }
     }

     public static void p(String msg)
     {
         System.out.println(msg);
     }

     public static String read0Line(String filePath)
     {
         FileInputStream fis = null;
         try {
             fis = new FileInputStream(filePath);
         } catch (FileNotFoundException e) {
             e.printStackTrace();
         }
         if(fis == null)
         {
             return null;
         }
         BufferedReader reader = new BufferedReader(new InputStreamReader(fis));
         try {
             String line0 = reader.readLine();
             //p(line0);
             return line0;
         } catch (IOException e) {
             e.printStackTrace();
         }finally{
             try {
                 reader.close();
                 fis.close();
             } catch (Exception e2) {
             }
         }
         return null;
     }

     public static int toInt(String str)
     {
         int ret = 0;
         try{
             ret = Integer.valueOf(str);
         }catch(Exception e)
         {
             ret = 0;
         }
         return ret;
     }

 }

执行：

 [jevan@media pname]$ time java PrintPID

 real    0m0.150s
 user    0m0.098s
 sys     0m0.056s
 [jevan@media pname]$ time ./dir

 real    0m0.019s
 user    0m0.000s
 sys     0m0.005s
 [jevan@media pname]$