一、前言：要在程序中启动某一程序，如果程序已经存在了，就不再启动。查找了N篇文档，有所收获，总结一下。
二、实现
大体分两种：
1、exec或popen执行ps的命令行，然后运用某几个字符串匹配函数。
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <signal.h>
int main()
{
FILE *pstr; char cmd[128],buff[512],*p;
pid_t pID;
int pidnum;
char *name= "ping ";//要查找的进程名
int ret=3;
memset(cmd,0,sizeof(cmd));
sprintf(cmd, "ps -ef|grep %s ",name);
pstr=popen(cmd, "r");//
if(pstr==NULL)
{ return 1; }
memset(buff,0,sizeof(buff));
fgets(buff,512,pstr);
p=strtok(buff, " ");
p=strtok(NULL, " "); //这句是否去掉，取决于当前系统中ps后，进程ID号是否是第一个字段 pclose(pstr);
if(p==NULL)
{ return 1; }
if(strlen(p)==0)
{ return 1; }
if((pidnum=atoi(p))==0)
{ return 1; }
printf("pidnum: %d\n",pidnum);
pID=(pid_t)pidnum;
ret=kill(pID,0);//这里不是要杀死进程，而是验证一下进程是否真的存在，返回0表示真的存在
printf("ret= %d \n",ret);
if(0==ret)
printf("process: %s exist!\n",name);
else printf("process: %s not exist!\n",name);
return 0;
}
2、读取/proc文件
找到个代码如下：
读取/proc文件查找进程
#ifndef __cplusplus//识别C/C++的宏，望文生意
#define _GNU_SOURCE
#endif
#include <unistd.h>
#include <dirent.h>
#include <sys/types.h> // for opendir(), readdir(), closedir()
#include <sys/stat.h> // for stat()
#ifdef __cplusplus
#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cstdarg>
#else
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>
#endif
#define PROC_DIRECTORY "/proc/"
#define CASE_SENSITIVE 1
#define CASE_INSENSITIVE 0
#define EXACT_MATCH 1
#define INEXACT_MATCH 0
//是不是数字
int IsNumeric(const char* ccharptr_CharacterList)
{
for ( ; *ccharptr_CharacterList; ccharptr_CharacterList++)
if (*ccharptr_CharacterList < '0' || *ccharptr_CharacterList > '9')
return 0; // false
return 1; // true
}
//intCaseSensitive=0大小写不敏感
int strcmp_Wrapper(const char *s1, const char *s2, int intCaseSensitive)
{
if (intCaseSensitive)
return !strcmp(s1, s2);
else
return !strcasecmp(s1, s2);
}
//intCaseSensitive=0大小写不敏感
int strstr_Wrapper(const char* haystack, const char* needle, int intCaseSensitive)
{
if (intCaseSensitive)
return (int) strstr(haystack, needle);
else
return (int) strcasestr(haystack, needle);
}
#ifdef __cplusplus
pid_t GetPIDbyName(const char* cchrptr_ProcessName, int intCaseSensitiveness, int intExactMatch)
#else
pid_t GetPIDbyName_implements(const char* cchrptr_ProcessName, int intCaseSensitiveness, int intExactMatch)
#endif
{
char chrarry_CommandLinePath[100] ;
char chrarry_NameOfProcess[300] ;
char* chrptr_StringToCompare = NULL ;
pid_t pid_ProcessIdentifier = (pid_t) -1 ;
struct dirent* de_DirEntity = NULL ;
DIR* dir_proc = NULL ;
int (*CompareFunction) (const char*, const char*, int) ;
if (intExactMatch)
CompareFunction = &strcmp_Wrapper;
else
CompareFunction = &strstr_Wrapper;
dir_proc = opendir(PROC_DIRECTORY) ;
if (dir_proc == NULL)
{
perror("Couldn't open the " PROC_DIRECTORY " directory") ;
return (pid_t) -2 ;
}
// Loop while not NULL
while ( (de_DirEntity = readdir(dir_proc)) )
{
if (de_DirEntity->d_type == DT_DIR)
{
if (IsNumeric(de_DirEntity->d_name))
{
strcpy(chrarry_CommandLinePath, PROC_DIRECTORY) ;
strcat(chrarry_CommandLinePath, de_DirEntity->d_name) ;
strcat(chrarry_CommandLinePath, "/cmdline") ;
FILE* fd_CmdLineFile = fopen (chrarry_CommandLinePath, "rt") ; //open the file for reading text
if (fd_CmdLineFile)
{
fscanf(fd_CmdLineFile, "%s", chrarry_NameOfProcess) ; //read from /proc/<NR>/cmdline
fclose(fd_CmdLineFile); //close the file prior to exiting the routine
if (strrchr(chrarry_NameOfProcess, '/'))
chrptr_StringToCompare = strrchr(chrarry_NameOfProcess, '/') +1 ;
else
chrptr_StringToCompare = chrarry_NameOfProcess ;
//printf("Process name: %s\n", chrarry_NameOfProcess);
//这个是全路径，比如/bin/ls
//printf("Pure Process name: %s\n", chrptr_StringToCompare );
//这个是纯进程名，比如ls
//这里可以比较全路径名，设置为chrarry_NameOfProcess即可
if ( CompareFunction(chrptr_StringToCompare, cchrptr_ProcessName, intCaseSensitiveness) )
{
pid_ProcessIdentifier = (pid_t) atoi(de_DirEntity->d_name) ;
closedir(dir_proc) ;
return pid_ProcessIdentifier ;
}
}
}
}
}
closedir(dir_proc) ;
return pid_ProcessIdentifier ;
}
#ifdef __cplusplus
pid_t GetPIDbyName(const char* cchrptr_ProcessName)
{
return GetPIDbyName(cchrptr_ProcessName, CASE_INSENSITIVE, EXACT_MATCH) ;
}
#else
// C cannot overload functions - fixed
/*这里是原文的实现，但貌似需要某些牛X的设置，因不需要，删之
pid_t GetPIDbyName_Wrapper(const char* cchrptr_ProcessName, ... )
{
int intTempArgument ;
int intInputArguments[2] ;
// intInputArguments[0] = 0 ;
// intInputArguments[1] = 0 ;
memset(intInputArguments, 0, sizeof(intInputArguments) ) ;
int intInputIndex ;
va_list argptr;
va_start( argptr, cchrptr_ProcessName );
for (intInputIndex = 0; (intTempArgument = va_arg( argptr, int )) != 15; ++intInputIndex)
{
intInputArguments[intInputIndex] = intTempArgument ;
}
va_end( argptr );
return GetPIDbyName_implements(cchrptr_ProcessName, intInputArguments[0], intInputArguments[1]);
}
#define GetPIDbyName(ProcessName,...) GetPIDbyName_Wrapper(ProcessName, ##__VA_ARGS__, (int) 15)
*/
//简单实现
pid_t GetPIDbyName_Wrapper(const char* cchrptr_ProcessName)
{
return GetPIDbyName_implements(cchrptr_ProcessName, 0,0);//大小写不敏感
}
#endif
int main()
{
pid_t pid = GetPIDbyName_Wrapper("bash") ; // If -1 = not found, if -2 = proc fs access error
printf("PID %d\n", pid);
return EXIT_SUCCESS ;
}
通过比较全路径，能一定程度上避免第1种方法的问题。
以下是整理后的C语言实现：
#include <unistd.h>
#include <dirent.h>
#include <sys/types.h> // for opendir(), readdir(), closedir()
#include <sys/stat.h> // for stat()
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdarg.h>
#define PROC_DIRECTORY "/proc/"
#define CASE_SENSITIVE 1
#define CASE_INSENSITIVE 0
#define EXACT_MATCH 1
#define INEXACT_MATCH 0
//是不是数字
int IsNumeric(const char* ccharptr_CharacterList)
{
for ( ; *ccharptr_CharacterList; ccharptr_CharacterList++)
if (*ccharptr_CharacterList < '0' || *ccharptr_CharacterList > '9')
return 0; // false
return 1; // true
}
//intCaseSensitive=0大小写不敏感
int strcmp_Wrapper(const char *s1, const char *s2, int intCaseSensitive)
{
if (intCaseSensitive)
return !strcmp(s1, s2);
else
return !strcasecmp(s1, s2);
}
//intCaseSensitive=0大小写不敏感
int strstr_Wrapper(const char* haystack, const char* needle, int intCaseSensitive)
{
if (intCaseSensitive)
return (int) strstr(haystack, needle);
else
return (int) strcasestr(haystack, needle);
}
pid_t GetPIDbyName_implements(const char* cchrptr_ProcessName, int intCaseSensitiveness, int intExactMatch)
{
char chrarry_CommandLinePath[100] ;
char chrarry_NameOfProcess[300] ;
char* chrptr_StringToCompare = NULL ;
pid_t pid_ProcessIdentifier = (pid_t) -1 ;
struct dirent* de_DirEntity = NULL ;
DIR* dir_proc = NULL ;
int (*CompareFunction) (const char*, const char*, int) ;
if (intExactMatch)
CompareFunction = &strcmp_Wrapper;
else
CompareFunction = &strstr_Wrapper;
dir_proc = opendir(PROC_DIRECTORY) ;
if (dir_proc == NULL)
{
perror("Couldn't open the " PROC_DIRECTORY " directory") ;
return (pid_t) -2 ;
}
// Loop while not NULL
while ( (de_DirEntity = readdir(dir_proc)) )
{
if (de_DirEntity->d_type == DT_DIR)
{
if (IsNumeric(de_DirEntity->d_name))
{
strcpy(chrarry_CommandLinePath, PROC_DIRECTORY) ;
strcat(chrarry_CommandLinePath, de_DirEntity->d_name) ;
strcat(chrarry_CommandLinePath, "/cmdline") ;
FILE* fd_CmdLineFile = fopen (chrarry_CommandLinePath, "rt") ; //open the file for reading text
if (fd_CmdLineFile)
{
fscanf(fd_CmdLineFile, "%s", chrarry_NameOfProcess) ; //read from /proc/<NR>/cmdline
fclose(fd_CmdLineFile); //close the file prior to exiting the routine
if (strrchr(chrarry_NameOfProcess, '/'))
chrptr_StringToCompare = strrchr(chrarry_NameOfProcess, '/') +1 ;
else
chrptr_StringToCompare = chrarry_NameOfProcess ;
//printf("Process name: %s\n", chrarry_NameOfProcess);
//这个是全路径，比如/bin/ls
//printf("Pure Process name: %s\n", chrptr_StringToCompare );
//这个是纯进程名，比如ls
//这里可以比较全路径名，设置为chrarry_NameOfProcess即可
if ( CompareFunction(chrptr_StringToCompare, cchrptr_ProcessName, intCaseSensitiveness) )
{
pid_ProcessIdentifier = (pid_t) atoi(de_DirEntity->d_name) ;
closedir(dir_proc) ;
return pid_ProcessIdentifier ;
}
}
}
}
}
closedir(dir_proc) ;
return pid_ProcessIdentifier ;
}
//简单实现
pid_t GetPIDbyName_Wrapper(const char* cchrptr_ProcessName)
{
return GetPIDbyName_implements(cchrptr_ProcessName, 0,0);//大小写不敏感
}
int main()
{
pid_t pid = GetPIDbyName_Wrapper("bash") ; // If -1 = not found, if -2 = proc fs access error
printf("PID %d\n", pid);
return EXIT_SUCCESS ;
}
