C strcmp中的字符串比较

Question

I have domain names stored in a 2 dimensional array of char

char domainNames[2][4096]= {"www.yahoo.com","java.sun.com"};

and I need to check if a given domain name stored in another array( char data[4096]; ) exists in the list, if the domain name is found, store all the IP addresses found in char IP[2][4096]= {"87.248.122.122","192.9.162.55"}; separated by "#" in the array char msg[4096];

this is the way I did it:

  for (i=0; i< 2;i++)
  {
    if(strcmp(domainNames[i], data)==0)
    {
      strcat(msg, IP[i]);
      strcat(msg, "#");
      found = true;
    }
  }

  if(!found)
    strcpy(msg,"IP not found");

  break;
}

The problem is that the result is always "IP not found" even if the string does exist.

Answer 1

Since you have a problem with newline characters being left on the input, you can just apply a simple check for the newline character and remove it if present:

size_t ln = strlen(data) - 1;
if ((ln > 0) && (data[ln] == '\n'))
    data[ln] = '\0';
for (i=0; i< 2;i++)
{
  if(strcmp(domainNames[i], data)==0)
  {
    strcat(msg, IP[i]);
    strcat(msg, "#");
    found = true;
  }

Because you're getting your input ( data ) from an external source, it would probably serve you well to thoroughly verify this prior to doing anything with it. Make a new function and pass data to it, verify you've stripped newlines, make sure there are no white space characters, make sure it ends with ".com" or whatever... anything that comes from an external source should be validated to the best of your ability before using it, not only to help with debugging, but also to avoid attacks (intentional or not).

Also, just a slight (possible) optimization for you, if msg is empty prior to this function, you can always just check for a 0 length and remove the extra found Boolean that way.