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
",__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 -1;
    }

    while((dirp = readdir(dp)) != NULL)
    {
        if(strcmp(dirp->d_name,".") == 0 ||strcmp(dirp->d_name,"..")==0)
        {
            continue;
        }
        int pid = atoi(dirp->d_name);
        //printf("pid =%d
",pid);
        if(pid == 0)
        {
            continue;
        }
        int ret = myfunc(pid);
        if(ret != 0)
        {
            printf("parse error!
");
            return -1;
        }
    }
    if(closedir(dp) < 0)
    {
        printf("cant't close directory /proc");
        return -1;
    }
    return 0;
}
static int
myfunc(int pid)
{
    char path[128]={0};
    const char *name="Name:";
    const char *state = "State:";
    char pname[32] = {0};

    sprintf(path,"/proc/%d/status",pid);
    if(access(path,F_OK)!=0)
    {
        printf("%s not exist.
",path);
        return -1;
    }

    int fd = open(path,O_RDONLY);
    if(fd<0)
    {
        perror("open");
        return -1;
    }

    char buf[1024]={0};
    int length = read(fd,buf,sizeof(buf));
    if(length<0)
    {
        perror("read");
        close(fd);
        return -1;
    }
    char *p0 =strstr(buf,name);
    char *p1 =strstr(buf,state);
    memcpy(pname,p0+strlen(name)+1,p1-p0-strlen(name)-2);
    printf("pname:%s
",pname);



    close(fd);

    return 0;
}

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]$