C++进程PID编程

一 获取pid_t的字节长度 

1 代码

#include <iostream>

using namespace std;

int main(int argc, char *argv[])
{
    pid_t pid;
    cout <<"sizeof(pid_t)="<< sizeof(pid_t) << endl;     
    return 0;
}

2 运行结果

[root@localhost test]# g++ test.cpp -o test
[root@localhost test]# ./test
sizeof(pid_t)=4

二 获取当前进程的ID

1 代码

#include <iostream>
#include <unistd.h>
using namespace std;

int main(int argc, char *argv[])
{
    pid_t pid = getpid();
    cout <<"pid="<<pid << endl;     
    return 0;
}

2 运行结果

[root@localhost test]# g++ test.cpp -o test
[root@localhost test]# ./test
pid=1006

三 通过PID文件判断进程是否运行

1 代码

#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <signal.h>

static  char starter_pid_file_default[] =  "/var/run/test.pid";


static bool check_pid(char *pid_file)
{
    struct stat stb;
    FILE *pidfile;

    if (stat(pid_file, &stb) == 0)
    {
        pidfile = fopen(pid_file, "r");
        if (pidfile)
        {
            char buf[64];
            pid_t pid = 0;
            memset(buf, 0, sizeof(buf));
            if (fread(buf, 1, sizeof(buf), pidfile))
            {
                buf[sizeof(buf) - 1] = '\0';
                pid = atoi(buf);
            }
            fclose(pidfile);
            if (pid && kill(pid, 0) == 0)
            {    /* such a process is running */
                printf("pid=%d",pid);
                return 1;
            }
        }
        printf("removing pidfile '%s', process not running", pid_file);
        unlink(pid_file);
    }
    return 0;
}


int main()
{
    FILE *fd = fopen(starter_pid_file_default, "w");

    if (fd)
    {
        fprintf(fd, "%u\n", getpid());
        fclose(fd);
    }
    if (check_pid(starter_pid_file_default))
    {
        printf("test is already running (%s exists)\n", starter_pid_file_default);
        
    }
    else
        printf("test is NOT running (%s NOT exists)\n", starter_pid_file_default);
    
    unlink(starter_pid_file_default);
    
    
    return 0;
    
}

2 运行结果

[root@localhost test]# g++ test.cpp -o test
[root@localhost test]# ./test
pid=1016test is already running (/var/run/test.pid exists)