fork,exec族函数的使用

exec用被执行的程序完全替换调用它的程序的影像。

fork创建一个新的进程就产生了一个新的PID，exec启动一个新程序，替换原有的进程，因此这个新的被exec执行的进程的PID不会改变，和调用exec函数的进程一样。

#include <uniSTd.h>

　　int execl(cONst char *path, const char *arg, ...);

　　int execlp(const char *file, const char *arg, ...);

　　int execle(const char *path, const char *arg, ..., char *const envp[]);

　　int execv(const char *path, char *const argv[]);

　　int execvp(const char *file, char *const argv[]);

　　int execve(const char *path, char *const argv[], char *const envp[]);

　　exec函数族装入并运行程序pathname，并将参数arg0(arg1,arg2,argv[],envp[])传递给子程序，出错返回-1。在exec函数族中，后缀l、v、p、e添加到exec后，所指定的函数将具有某种操作能力有后缀：

　　其中只有execve是真正意义上的系统调用，其它都是在此基础上经过包装的库函数。

自己写的一个编译程序的代码（待完善

/*
 * =====================================================================================
 *
 *       Filename:  temp.c
 *
 *    Description:  
 *
 *        Version:  1.0
 *        Created:  2012年01月06日 19时35分59秒
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  MaZheng (blog.youkuaiyun.com/mazheng1989), mazheng19891019@gmail.com
 *        Company:  Dalian University Of Technology
 *
 * =====================================================================================
 */

#include <unistd.h>
#include <ios>
#include <iostream>
#include <fstream>
#include <string>
#include	<string.h>
using namespace std;
//
//
// process_mem_usage(double &, double &) - takes two doubles by reference,
// attempts to read the system-dependent data for a process' virtual memory
// size and resident set size, and return the results in KB.
//
// On failure, returns 0.0, 0.0

void process_mem_usage(double& vm_usage, double& resident_set)
{
   using std::ios_base;
   using std::ifstream;
   using std::string;

   vm_usage     = 0.0;
   resident_set = 0.0;

   // 'file' stat seems to give the most reliable results
   //
   ifstream stat_stream("/proc/self/stat",ios_base::in);

   // dummy vars for leading entries in stat that we don't care about
   //
   string pid, comm, state, ppid, pgrp, session, tty_nr;
   string tpgid, flags, minflt, cminflt, majflt, cmajflt;
   string utime, stime, cutime, cstime, priority, nice;
   string O, itrealvalue, starttime;

   // the two fields we want
   //
   unsigned long vsize;
   long rss;

   stat_stream >> pid >> comm >> state >> ppid >> pgrp >> session >> tty_nr
               >> tpgid >> flags >> minflt >> cminflt >> majflt >> cmajflt
               >> utime >> stime >> cutime >> cstime >> priority >> nice
               >> O >> itrealvalue >> starttime >> vsize >> rss; // don't care about the rest

   stat_stream.close();

   long page_size_kb = sysconf(_SC_PAGE_SIZE) / 1024; // in case x86-64 is configured to use 2MB pages
   vm_usage     = vsize / 1024.0;
   resident_set = rss * page_size_kb;
}
int main(int argv,char **args)
{
	pid_t pid=fork();
	if(pid!=0)
		return 0;

   if(argv>0)
   {
	   int len=strlen(args[1]);
	   printf("%d\n",len);
	   if(args[1][len-1]=='c'&&args[1][len-2]=='.')
	   {
		   char *str=new char[len+3];
		   memcpy(str+2,args[1],len);
		   str[len+2]='\0';
		   str[len+1]='o';
		   str[0]='.';
		   str[1]='/';
		  pid=fork();
		  if(pid!=0)
		  {
		    execl("/usr/bin/gcc","gcc","-o",str,args[1],NULL);
			return 0;
		  }
		  else
		  {
			  printf("zhixing%s %s\n",args[1],str);
		      execv(str,NULL);
			  printf("mazheng\n");
		  }
	   }
   }
   using std::cout;
   using std::endl;
   double vm, rss;
   process_mem_usage(vm, rss);
   cout << "VM: " << vm << " RSS: " << rss << endl;
}