Cannot understand code snippet

[pbindahouse 0]

Can anyone do a better job explaining this code to me? it is from a launchpad script that hooks a launchpad up to a serial LCD from sparkfun. It has to do with packing data to send via UART to the LCD but I cannot understand it. 

 

Thanks 

// base-10 itoa for positive numbers. Populates str with a null-terminated string.
// limit lets you overflow back to 1 when you hit the limit+1, 2*limit+1, ...
// make sure *str is an array that can hold the number of digits in your limit + 1.
void itoa(unsigned int val, char *str, unsigned int limit)
{
  int temploc = 0;
  int digit = 0;
  int strloc = 0;
  char tempstr[5]; //16-bit number can be at most 5 ASCII digits;

  if(val>limit)
    val %= limit;

  do
  {
    digit = val % 10;
    tempstr[temploc++] = digit + '0';
    val /= 10;
  } while (val > 0);

  // reverse the digits back into the output string
  while(temploc>0)
    str[strloc++] = tempstr[--temploc];

  str[strloc]=0;
}

[JWoodrell 285]

ok, i understand it.

 

the function is an integer to ascii converter so it takes 12345 as a number and encodes it as the text characters '1' , '2' , '3' , '4' , '5'

// base-10 itoa for positive numbers. Populates str with a null-terminated string.
// limit lets you overflow back to 1 when you hit the limit+1, 2*limit+1, ...
// make sure *str is an array that can hold the number of digits in your limit + 1.
void itoa(unsigned int val, char *str, unsigned int limit)  //  <-- function takes an integer as an input and transforms it into a proper string for output.  *str is the string that it will modify as an output.
{
int temploc = 0;
int digit = 0;
int strloc = 0;
char tempstr[5]; //16-bit number can be at most 5 ASCII digits;

if(val>limit)
val %= limit;  // % is a modulus command it basically means "what's left over" think long division.  so say 26 / 10 = 2 with a 6 as remainder  well the whole number portion is ignored, and the remainder is the answer...  so 26 % 10 = 6
//  this line clips the input to a known maximum value  useful when your output display only has a set number of digits
do
{
digit = val % 10;  //clip the input number down to just the first digit (remember anything above 10 is clipped and rolls over)
tempstr[temploc++] = digit + '0'; set that position of the string to that single digit value, as well as +'0' to build up the string.
val /= 10; //  cut the bottom digit off the number (this is integer math so there are no decimals)
} while (val > 0);  //as long as there are any numbers left, wash rinse repeat this cycle to encode the entire number into the string.

// reverse the digits back into the output string
while(temploc>0)  //  the temploc variable built up as the temp string was built during the previous step now for each character (which added 1 to temploc)
str[strloc++] = tempstr[--temploc]; //copy the character at each position from the temp string into the output string.

str[strloc]=0; // place a 0 at the end of the output string as a null terminator
}

hope that helps, or if you need anything else explained or expanded on

[roadrunner84 466]

If the number is above limit, the number "wraps" over the limit. So if you set limit to 99, you guarantee that the result will be a two digit number.

Then the number is iteratively divided by 10, resulting in a single digit remainder, starting from the least significant digit.

As a string is built with the most significant digit first, the string is built iteratively by counting back through the result indexes.

 

By adding '0' (the character zero) to a number, this results in the corresponding character for that digit.

 

As a last step, the "string terminator" must be added to the end of the string, this is the character 0 (not '0', which represents the number zero, but the zeroeth character  - also called null - is the string terminator)

[spirilis 1,265]

Note that if it adds the null terminator at the end, but still supports 5 ASCII digits, it should be a 6-byte array, not 5... i.e. char tempstr[6];