Efficiently escaping quotes in C before passing to mysql_query

Question

In a nutshell I typically build a MySQL query within C using sprintf

i.e.

sprintf(sqlcmd,\"update foo set dog=\\\"lab\\\" where description=\\\"%s\\\         


        

Answer 1

Although MySQL has a mysql_real_escape_string() function, you should probably be using prepared statements instead, which allow you to use ? placeholders instead of real parameters, and then bind them to the real parameters before each execution of the statement.

Answer 2

MySQL does that already for you

http://dev.mysql.com/doc/refman/5.0/en/mysql-real-escape-string.html

Answer 3

I would write a simple escape function like the following:

size_t escape_mysql_string(const char * input, size_t input_size,
   char * output, size_t output_size)
{
   unsigned long ipos; // position within input buffer
   unsigned long opos; // position within output buffer

   // quick check to verify output buffer is at least as large as input buffer
   if (output_size < (input_size+2))
      return(0);

   // loop through input buffer
   opos = 0;
   for(ipos = 0; ((ipos < input_size) && (input[ipos])); ipos++)
   {
      // verify that output buffer has room for escaped input
      if ((opos+2) >= output_size)
      {
         output[opos] = '\0';
         return(opos);
      };

      switch(input[ipos])
      {
         // escape ("""), ("'"), ("\"), ("%"), and ("_") characters
         case '\'':
         case '\"':
         case '\\':
         case '%':
         case '_':
         output[opos] = '\\';
         opos++;
         output[opos] = input[ipos];
         break;

         // escape newlines
         case '\n':
         output[opos] = '\\';
         opos++;
         output[opos] = 'n';
         break;

         // escape carriage returns
         case '\r':
         output[opos] = '\\';
         opos++;
         output[opos] = 'r';
         break;

         // escape tabs
         case '\t':
         output[opos] = '\\';
         opos++;
         output[opos] = 't';
         break;

         // save unescapd input character
         default:
         output[opos] = input[ipos];
         break;
      };
      opos++;
   };

   output[opos] ='\0';
   return(opos);
}

The call it with something like the following:

char some_escaped_desc[1024];
escape_mysql_string(some_desc, strlen(some_desc), some_escaped_desc, 1024);