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sprintf() messing with stored values

 
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javick82



Joined: 12 Jul 2007
Posts: 43

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sprintf() messing with stored values
PostPosted: Fri Aug 03, 2007 11:57 am     Reply with quote

I have been messing with a code to test a concept I have for a project I am working on. I want a function that performs a command based on a string input. (see print_numbers() for a crude example).

The problem I am facing is when I use sprintf(str,"%c%c%c",getc(),getc(),getc()) the variable "value" gets messed up. But, when "value" is written to "holder", sprintf() is performed, and "holder" is written back to "value", the function works properly. I would like to use sprintf() to define the function parameter obviously w/o the dummy variable so the code is more readable (applies to application, not this test file).

Compiler >v4.0

Code:
#include <16f877a.h>
#fuses HS,NOLVP,NOWDT,PUT
#use delay(clock = 20000000)
#use RS232(baud = 9600, xmit = PIN_C6, rcv = PIN_C7)

void print_numbers(int number, char *output)
{
   printf("Data:\n\r%c%c%c\n\r%u\n\r",output[0],output[1],output[2],number);
   if(output[0] == 'h' && output[1] == 'e' && output[2] == 'x')
      printf("Value in hex: 0x%x\n\r", number);
   else
   {
      if(output[0] == 'b' && output[1] == 'i' && output[2] == 'n')
         printf("Can't print binary numbers\n\r");
      else
      {
         if(output[0] == 'd' && output[1] == 'e' && output[2] == 'c')
            printf("Value in dec: %u\n\r", number);
         else
            printf("OOPS!");
      }
   }
}   


void main()
{
   char command[3];
   int value;
   int holder;
   while(1)
   {
      printf("\n\rEnter value (000-255):\n\r");
      value = 100*(getc()-48);
      printf("\n\r%u\n\r",value);
      value = value+(10*(getc()-48));
      printf("\n\r%u\n\r",value);
      value = value+(getc()-48);
      printf("\n\r%u\n\r",value);
      //holder = value;
      printf("\n\rEnter output format (hex/bin/dec):\n\r");
      sprintf(command, "%c%c%c", getc(),getc(),getc());
      //value = holder;
      printf("\n\r%u\n\r",value);
      print_numbers(value, command);
   }
}


Thanks!
javick82



Joined: 12 Jul 2007
Posts: 43

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Never mind
PostPosted: Fri Aug 03, 2007 12:06 pm     Reply with quote

Just needed an extra character in the array:
Code:

char command[4];

works.
SET



Joined: 15 Nov 2005
Posts: 161
Location: Glasgow, UK

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PostPosted: Fri Aug 03, 2007 12:10 pm     Reply with quote

Your buffer -

Code:
char command[3];
int value;


needs 4 bytes, not 3 - sprintf appends a null and hence over-writes 'value'.

I see you noticed it but I'll post anyway Smile
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