1

我想在文件文本中保存一些信息，我写了这个程序：

    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>


int main(int argc,char *argv[])
 {
     FILE *fichier;
     char buffer[20];
     char command[200];
     char command1[100];


     system(" cat /etc/resolv.conf  | grep nameserver | awk -F' ' '{print $2}' | cut -d'.' -f1-3 | awk '{print $1\".1\"}' > ethernet_dns.txt");

     fichier=fopen("ethernet_dns.txt","r");
     memset(&buffer,0,sizeof(buffer));
     fread(buffer,20,1,fichier);
     printf("buffer is: %s",buffer);

     snprintf(command,sizeof(command),"ping -c 1 -W 1  %s > /tmp/ping_result",buffer);
      printf("command is: %s",command);

     system(command);


     return 0;
 }

结果：

buffer is: 127.0.1.1
command is : ping -c 1 -W 1 127.0.1.1

系统命令返回：

    PING 127.0.1.1 (127.0.1.1) 56(84) bytes of data.
64 bytes from 127.0.1.1: icmp_seq=1 ttl=64 time=0.115 ms

--- 127.0.1.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.115/0.115/0.115/0.000 ms

但是当我运行时： cat /tmp/ping_result.I 有一个空文件

4

2 回答 2

0

问题：代码正在读取'\n'，buffer[]但尝试将其作为命令的一部分。需要修剪缓冲区。*** 以下

 // Insure file is open
 fichier=fopen("ethernet_dns.txt","r");
 assert(fichier);

 // Use fgets
 //memset(&buffer,0,sizeof(buffer));
 //fread(buffer,20,1,fichier);
 if (fgets(buffer, sizeof buffer, fichier)) {

   // lop off potential \n
   buffer[strcspn(buffer, "\n")] = '\0';  // ***

   printf("buffer is: <%s>\n",buffer);

   int n = snprintf(command, sizeof(command), "ping -c 1 -W 1  %s > /tmp/ping_result", 
     buffer);
   printf("command is: <%s>\n",command);

   // Only issue command if no problems occurred in snprintf()
   if (n > 0 && n < sizeof(command)) system(command);
于 2016-10-11T14:35:42.950 回答
0

发布的代码有几个问题

1) 将结果输出ping到标准输出而不是输出到/tmp/ping_result

2) 未能从buffer[]数组中删除尾随换行符

以下代码

1）清理缩进

2) 更正代码中的问题

3) 处理调用失败的可能fopen()

4) 消除不需要的最终语句：return 0

#include <stdio.h>
#include <stdlib.h>
#include <string.h>


int main( void )
{
     FILE *fichier;
     char buffer[20];
     char command[200];



     system(" cat /etc/resolv.conf  | grep nameserver | awk -F' ' '{print $2}' | cut -d'.' -f1-3 | awk '{print $1\".1\"}' > ethernet_dns.txt");

     fichier=fopen("ethernet_dns.txt","r");
     if( !fichier )
     {
         perror( "fopen for ethernet_dns.txt failed");
         exit( EXIT_FAILURE );
     }

     // implied else, fopen successful

     memset(buffer,0,sizeof(buffer));
     size_t len = fread(buffer,1, sizeof(buffer),fichier);
     printf( "len is: %lu\n", len );
     buffer[len-1] = '\0'; // eliminates trailing newline
     printf("buffer is: %s\n",buffer);

     snprintf(command,sizeof(command),"ping -c 1 -W 1 ");
     strcat( command, buffer);
     strcat( command, " > /tmp/ping_result");
     printf("command is: %s\n",command);

     system(command);
}

在我的计算机上生成的输出在文件中：/tmp/ping_result

PING 127.0.1.1 (127.0.1.1) 56(84) bytes of data.
64 bytes from 127.0.1.1: icmp_seq=1 ttl=64 time=0.046 ms

--- 127.0.1.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.046/0.046/0.046/0.000 ms
于 2016-10-12T20:51:29.027 回答