String appears to change on its own

This is a discussion on String appears to change on its own within the C Programming forums, part of the General Programming Boards category; Hi i am working on this program. I have looked over it and i cannot determine an explanation for its ...

  1. #1
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    String appears to change on its own

    Hi i am working on this program. I have looked over it and i cannot determine an explanation for its behavior. Can someone help explain why and how to overcome this issue? Thanks a bunch.

    Code:
    #include <string.h>
    #include <stdio.h>
    
    int
    main ()
    {
      char *the_message = "42.77417833333333|-78.31375166666667";
      char latitude[17];
      char longitude[17];
      int lat_counter_x = 0;
      int long_counter_x = 0;
      int long_counter_y = 0;
      int pipe_location;
    
      for (lat_counter_x = 0; lat_counter_x <= strlen (the_message);
           lat_counter_x++)
        {
          if (the_message[lat_counter_x] == '|')
            {
              pipe_location = lat_counter_x;        //shows character location of | - separates lat/long numbers
            }
        }
    
      if (pipe_location)
        {
          for (lat_counter_x = 0; lat_counter_x < (pipe_location - 1);
               lat_counter_x++)
            {
              latitude[lat_counter_x] = the_message[lat_counter_x];
            }
          latitude[lat_counter_x + 1] = '\0';
        }
      printf ("Latitude: %s\n", latitude);  // displays properly 42.77417833333333
      for (long_counter_x = (pipe_location + 1);
           long_counter_x <= strlen (the_message); long_counter_x++)
        {
          longitude[long_counter_y] = the_message[long_counter_x];
          long_counter_y++;
        }
      longitude[long_counter_y] = '\0';
      printf ("Longitude: %s\n", longitude);        // displays properly -78.31375166666667
      printf ("Latitude: %s\n", latitude);  //the number changes .... why? - latitude is now the last char of longitude
      printf ("Longitude: %s\n", longitude);        // displays properly -78.31375166666667
    }
    
    //If i comment out the second for loop, latitude is not affected.
    
    /* Output
    Latitude: 42.7741783333333
    Longitude: -78.31375166666667
    Latitude: 7
    Longitude: -78.31375166666667
    */

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    Code:
             1111111111
    1234567890123456789
    
    -78.31375166666667n
    The n is the \0 character. What are the odds that a 17-character array is long enough to hold this? (Hint: not good.)

  3. #3
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    Why don't you use standard function like strchr(),strcpy() ?

  4. #4
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    Quote Originally Posted by Bayint Naung View Post
    Why don't you use standard function like strchr(),strcpy() ?
    Beat me to it... I was just going to say that all that could probably be reduced to about 5 lines of code using strtok() to find the pipe symbol and then he doesn't even need to use strcpy. But in this case I agree strchr() might be easier.

    Code:
      char *the_message; //= "42.77417833333333|-78.31375166666667";  
      char *latitude = the_message;
      char *longitude = strchr(the_message,'|');
      the_message[longitude++] = 0;
      printf("Lat = %s  Long = %s\n",latitude,longitude);
    Of course it will grow a bit with error checking....
    Last edited by CommonTater; 01-22-2011 at 09:40 PM. Reason: for the overly critical....

  5. #5
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    LOL, Is it pseudo Code?!
    Modifying string literal is Undefined Behavior.

  6. #6
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    Quote Originally Posted by Bayint Naung View Post
    LOL, Is it pseudo Code?!
    Modifying string literal is Undefined Behavior.
    True... However; I would suspect in his final application that message comes from a GPS so we can call it a prediction... (See above)

    Moreover... have you ever read my sig at the bottom of every message?
    Last edited by CommonTater; 01-22-2011 at 09:41 PM.

  7. #7
    Registered User whiteflags's Avatar
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    Code:
      char *the_message; //= "42.77417833333333|-78.31375166666667";  
      char *latitude = the_message;
      char *longitude = strchr(the_message,'|');
      the_message[longitude++] = 0;
      printf("Lat = %s  Long = %s\n",latitude,longitude);
    Actually I'm a bit concerned that someone wouldn't know what to do anyway since a pointer is being used as an index here. Maybe the_message[longitude - latitude] = 0; is more correct.

  8. #8
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    Quote Originally Posted by whiteflags View Post
    Actually I'm a bit concerned that someone wouldn't know what to do anyway since a pointer is being used as an index here. Maybe the_message[longitude - latitude] = 0; is more correct.
    Got me on that one.... Yep... or *(latitude++) = 0; my mistake.

    Nice catch, btw.
    Last edited by CommonTater; 01-22-2011 at 10:05 PM.

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