打印pid，写着玩。

  1 #include <stdio.h>
  2 #include <string.h>
  3 #include <dirent.h>
  4 #include <limits.h>
  5 #include <unistd.h>
  6 #include <sys/stat.h>
  7 #include <sys/types.h>
  8 #include <fcntl.h>
  9 
 10 #define PROC "/proc/"
 11 
 12 
 13 typedef int Myfunc(int pid) ;
 14 static Myfunc  myfunc;
 15 
 16 
 17 #define P()     printf("%s:%d
",__FUNCTION__,__LINE__)
 18 static int dopath(Myfunc *func);
 19 
 20 int main(int argc,char *argv[])
 21 {
 22     return dopath(myfunc);
 23 }
 24 static int
 25 dopath(Myfunc *func)
 26 {
 27     //struct stat         statbuf;
 28     struct dirent        *dirp;
 29     DIR                    *dp;
 30     int                 ret;
 31     char                *ptr;
 32 
 33     //if()
 34     if((dp = opendir(PROC)) == NULL)
 35     {
 36         perror("open");
 37         return -1;
 38     }
 39 
 40     while((dirp = readdir(dp)) != NULL)
 41     {
 42         if(strcmp(dirp->d_name,".") == 0 ||strcmp(dirp->d_name,"..")==0)
 43         {
 44             continue;
 45         }
 46         int pid = atoi(dirp->d_name);
 47         //printf("pid =%d
",pid);
 48         if(pid == 0)
 49         {
 50             continue;
 51         }
 52         int ret = myfunc(pid);
 53         if(ret != 0)
 54         {
 55             printf("parse error!
");
 56             return -1;
 57         }
 58     }
 59     if(closedir(dp) < 0)
 60     {
 61         printf("cant't close directory /proc");
 62         return -1;
 63     }
 64     return 0;
 65 }
 66 static int
 67 myfunc(int pid)
 68 {
 69     char path[128]={0};
 70     const char *name="Name:";
 71     const char *state = "State:";
 72     char pname[32] = {0};
 73 
 74     sprintf(path,"/proc/%d/status",pid);
 75     if(access(path,F_OK)!=0)
 76     {
 77         printf("%s not exist.
",path);
 78         return -1;
 79     }
 80 
 81     int fd = open(path,O_RDONLY);
 82     if(fd<0)
 83     {
 84         perror("open");
 85         return -1;
 86     }
 87 
 88     char buf[1024]={0};
 89     int length = read(fd,buf,sizeof(buf));
 90     if(length<0)
 91     {
 92         perror("read");
 93         close(fd);
 94         return -1;
 95     }
 96     char *p0 =strstr(buf,name);
 97     char *p1 =strstr(buf,state);
 98     memcpy(pname,p0+strlen(name)+1,p1-p0-strlen(name)-2);
 99     printf("pname:%s
",pname);
100 
101 
102 
103     close(fd);
104 
105     return 0;
106 }

写几行代码来打印pid对应的进程名。

java版本：

  1 import java.io.BufferedReader;
  2 import java.io.File;
  3 import java.io.FileInputStream;
  4 import java.io.FileNotFoundException;
  5 import java.io.IOException;
  6 import java.io.InputStreamReader;
  7 import java.io.Reader;
  8 
  9 /**
 10  * @author jevan (jevan.cnblogs.com)
 11  * @version 1.0 at 2013-11-27
 12  *
 13  */
 14 public class PrintPID {
 15 
 16     /**
 17      * @param args
 18      */
 19     public static void main(String[] args) {
 20         printPid();
 21     }
 22     
 23     private static void printPid()
 24     {
 25         
 26         File proc = new File("/proc");
 27         for(File f:proc.listFiles())
 28         {
 29             if(f.getName().equals(".")||f.getName().equals(".."))
 30                 continue;
 31             
 32             if(f.isDirectory())
 33             {
 34                 int pid = toInt(f.getName());
 35                 if(pid == 0)
 36                     continue;
 37                 
 38                 File fname = new File("/proc/"+f.getName()+"/status");
 39                 
 40                 if(!fname.exists())
 41                     continue;
 42                 
 43                 
 44                 String line0 =read0Line("/proc/"+f.getName()+"/status");
 45                 
 46                 String[] tmp = line0.split(":",2);
 47                 if(tmp==null||tmp.length!=2)
 48                 {
 49                     continue;
 50                 }
 51                 p("==>"+tmp[1]);
 52                 
 53             }
 54         }
 55     }
 56 
 57     public static void p(String msg)
 58     {
 59         System.out.println(msg);
 60     }
 61 
 62     public static String read0Line(String filePath)
 63     {
 64         FileInputStream fis = null;
 65         try {
 66             fis = new FileInputStream(filePath);
 67         } catch (FileNotFoundException e) {
 68             e.printStackTrace();
 69         }
 70         if(fis == null)
 71         {
 72             return null;
 73         }
 74         BufferedReader reader = new BufferedReader(new InputStreamReader(fis));
 75         try {
 76             String line0 = reader.readLine();
 77             //p(line0);
 78             return line0;
 79         } catch (IOException e) {
 80             e.printStackTrace();
 81         }finally{
 82             try {
 83                 reader.close();
 84                 fis.close();
 85             } catch (Exception e2) {
 86             }
 87         }
 88         return null;
 89     }
 90     
 91     public static int toInt(String str)
 92     {
 93         int ret = 0;
 94         try{
 95             ret = Integer.valueOf(str);
 96         }catch(Exception e)
 97         {
 98             ret = 0;
 99         }
100         return ret;
101     }
102     
103 }

执行：

 1 [jevan@media pname]$ time java PrintPID
 2 
 3 real    0m0.150s
 4 user    0m0.098s
 5 sys     0m0.056s
 6 [jevan@media pname]$ time ./dir
 7 
 8 real    0m0.019s
 9 user    0m0.000s
10 sys     0m0.005s
11 [jevan@media pname]$