关于文件打开计数和setrlimit的用法

dilfish

代码如下：

int main(int argc,char** argv) { &nbsp;pid_t pid; &nbsp;pid = fork(); &nbsp;if(pid > 0) &nbsp;&nbsp;&nbsp;&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp; int i = 4; &nbsp;&nbsp;&nbsp;&nbsp; cout << "parent" << endl; &nbsp;&nbsp;&nbsp;&nbsp; while(i --) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; sleep(3); &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; cout << "sleep" << endl; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;else if(pid == 0) &nbsp;&nbsp;&nbsp;&nbsp;{ &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; rlimit rl; &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; rl.rlim_cur = 4; &nbsp;&nbsp;&nbsp;&nbsp; rl.rlim_max = 4; &nbsp;&nbsp;&nbsp;&nbsp; FILE* ho = freopen("result.out","w+",stdout); &nbsp;&nbsp;&nbsp;&nbsp; FILE* hi = freopen("arg","r+",stdin); &nbsp;&nbsp;&nbsp;&nbsp; if(setrlimit(RLIMIT_NOFILE,&rl)) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;cout << "setrlimit error" << endl; &nbsp;&nbsp;&nbsp;&nbsp; //cout << "in child" << endl; &nbsp;&nbsp;&nbsp;&nbsp; if(execl("./targ","targ",(char*)0)) &nbsp;&nbsp;&nbsp;&nbsp; cout << "abcdefg" << endl; &nbsp;&nbsp;&nbsp;&nbsp;} &nbsp;return 0; }

父进程只是等待。
子进程重定向了标准输入和标准输出之后，限定了能打开的文件数为4。
如果targ的功能是执行两个数的加法，而arg中是1 3。这时result.out中为4。
如果把限定能打开的文件数变为3，则程序执行失败，result.out的内容为cout << "abcdefg" << endl;
因为打开文件走过上限了，但是targ中并没有打开文件。如下：

#include<iostream> using namespace std; int main(int argc,char** argv) { &nbsp;int i,j; &nbsp;cin >> i >> j; &nbsp;cout << i + j; &nbsp;return 0; }

请问为什么打开文件数是4的时候可以运行，打开文件数限制为3时就被终止了。。。。。？