[avr-gcc-list] sprintf

[David VanHorn]

 

So I was using sprintf to create some data to send to the LCD, by way of lcd_puts.

I had a pair of arrays, A_String[17], and B_String[17] which I filled using two loops.

 

I hit some problems when I tried to consolidate this into one loop.

The symptom was that the second string wouldn't display, but it would if I had the two routines in separate loops.

I'm creating a simple bar graph, Data_A and Data_B have some value that is roughly between 0 and 16* the Step value.

 

  for (i=0; i<16; i++)
  {
   if ((Step * i) < Data_A) {
    sprintf((A_String+i), "%c", 0xFF);
   } else {
    sprintf((A_String+i), "%c", 0x20);
   }

   if ((Step * i) < Data_B) {
    sprintf((B_String+i), "%c", 0xFF);
   } else {
    sprintf((B_String+i), "%c", 0x20);
   }
  }

 

  lcd_home();
  lcd_gotoxy(0,0);
  lcd_puts(A_String); // String must be null terminated.
  lcd_gotoxy(0,1);
  lcd_puts(B_String);

In the above implementation, B_String would not show up on the display, but A_String would..

 

Below is the version that worked, the only difference is that the A string is completed before starting on the B string.

 

  for (i=0; i<16; i++)
  {
   if ((Step * i) < Data_A) {
    sprintf((A_String+i), "%c", 0xFF);
   } else {
    sprintf((A_String+i), "%c", 0x20);
   }

 

  for (i=0; i<16; i++)
  {

   if ((Step * i) < Data_B) {
    sprintf((B_String+i), "%c", 0xFF);
   } else {
    sprintf((B_String+i), "%c", 0x20);
   }
  }

 

It turned out that I had neglected to allow for the terminating null in the strings, but this raises two questions for me.

 

1: Why doesn't sprintf((A_String+16), "%c", 0x00); drop a null into the last element of A_String.

2: Why does the separate loops case work at all?

 

I solved my problem by inserting the null with

 memset((A_String+16), 0, 1); and the same for B_String.