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Problem with function " gets "

 
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umka



Joined: 28 Aug 2007
Posts: 99
Location: New Zealand

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Problem with function " gets "
PostPosted: Sun Mar 30, 2008 8:03 pm     Reply with quote
Here is my code. It doesnt seem to not want to come out of the gets routine because if i run the code the string "password" is outputted to the CCS serial monitor window so then i isend mike from the ascii line and then have to stop running the program coz nothing happens. the strings "word" and "password" are both set to "mike" but the compair (sttricmp) is not happening.

if i comment out the gets(word) and use strcpy(word,"mike") the program run fine in a continous loop outputting "pass"

Code:
#include <16F877a.H>
#device icd = true
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock = 4000000)
#use rs232(baud=9600, xmit=PIN_c6, rcv=PIN_c7, BITS =8, PARITY=n, stop=1)

#include <string.h>

char word[4];
char password[4];

   void main()
   { 
      strcpy(word,"");
      strcpy(password,"mike");
     
      while(true)
         {
         output_high(pin_d2);
         delay_ms(500);
         
         printf("Password: ");
         delay_ms(50);
         
         gets(word);
           
//         strcpy(word,"mike");

          if(stricmp(password,word))
         
            {printf("Pass");}
            else
            {printf("Fail");}
                           
                           
         output_low(pin_d2);
         delay_ms(500);
   
         }
   }
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Sun Mar 30, 2008 11:37 pm     Reply with quote
1. Your array is too small to hold a 4-character string.
The array size must be at least one element larger than the maximum
expected string size. That's because a string always has a 0x00 byte
at the end. This byte is inserted by gets().

2. Your code is unsafe. If the user types in more than the expected
number of characters, you will overwrite RAM beyond the limits of
your array and destroy other variables, possibly causing your
program to crash. It's much better to use the get_string() function.
See this thread for examples:
http://www.ccsinfo.com/forum/viewtopic.php?t=17563

3. Always put ERRORS in your #use rs232() statement, to prevent
possible lockups, when you use large delay_ms() values prior to
reading the UART. Use ERRORS in all your programs.
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