Thread: using malloc method to hold the converted data to string/char array

I would like to convert my code that uses an array that's constantly allocated to hold the converted data from an analog to digital converter into a method where the result of the sprintf conversion would be stored in a pointer as long as I need it. Below shows two versions of my code and the red highlighted line shows the task that I'm having trouble with. I apologize for the lackluster tab formatting of the code in advance. Thanks.

explicitly allocated char array version:

Code:

// Data Logging Scale                 <[email protected]>
// Created: Nov 3, 2007
// Revised: Nov 15, 2007

#include <built_in.h>
#include "typedefs.h"
#include "usart.h"
#include "LCD4.h"

#define BUFFER_SIZE 5

void delay(uint number)
{
      while(--number > 0);
}

void main() {
  uint temp_res, last_temp_res;
  int n;
  char adc[BUFFER_SIZE];            // temporary adc string value

  OSCCON = 0x70;        /* internal oscillator at 8 Mhz, system clock = internal oscillator*/
  OSCTUNE = 0x00;        /* oscillator tuning register at max frequency */
 	CMCON = 7;              // turn off comparators
 	Delay_ms(20);            // system wide delay of 20 ms
 	
  ADCON1 = 0x0e;          // Configure Vref and AN0
  TRISA  = 0x01;          // PORTA is output except RA0 (AN0)
  TRISB  = 0x00;          // all PORTB pins are output
  TRISC  = 0x00;          // PORTC is outputs
  
  LCD4_INIT();            // initialize the LCD
  LCD4_OUT("Weight (kg) : ");       // output some text
  

  while(1)
  {
    temp_res = Adc_Read(0);
    n = sprintf(adc, "%u", temp_res);
    if (n < 0 || n >= BUFFER_SIZE)
      break;
    if (abs(temp_res - last_temp_res) < 10)
    {
          LCD4_CMD(142);                   // move cursor position to character #15
          LCD4_OUT(adc);              // output the a/d result
    }
    last_temp_res = temp_res;
  }
}

malloc for a char pointer version:

Code:

// Data Logging Scale                 <[email protected]>
// Created: Nov 3, 2007
// Revised: Dec 15, 2007

#include <built_in.h>
#include "typedefs.h"
#include "usart.h"
#include "LCD4.h"

#define BUFFER_SIZE 5

void delay(uint number)
{
      while(--number > 0);
}

void main() {
  uint temp_res, last_temp_res;
  char *temp_res_text;               // dynamic character array pointer
  int n;

  OSCCON = 0x70;        /* internal oscillator at 8 Mhz, system clock = internal oscillator*/
 	OSCTUNE = 0x00;        /* oscillator tuning register at max frequency */
 	CMCON = 7;              // turn off comparators
 	Delay_ms(20);            // system wide delay of 20 ms
 	
  ADCON1 = 0x0e;          // Configure Vref and AN0
  TRISA  = 0x01;          // PORTA is output except RA0 (AN0)
  TRISB  = 0x00;          // all PORTB pins are output
  TRISC  = 0x00;          // PORTC is outputs
  
  LCD4_INIT();            // initialize the LCD
  LCD4_OUT("Weight (kg) : ");       // output some text

  while(1)
  {
     temp_res = Adc_Read(0);          // sample a/d converter
     
     temp_res_text = (char *) malloc(5);        // allocate 5 character bytes
     
     // How would i use sprintf function to convert temp_res data into string format
     // in resultant pointer temp_res_text?
     
     LCD4_CMD(142);                   // move cursor position to character #15
     LCD4_OUT(temp_res);              // output the a/d result
     
     free(temp_res_text);             // free allocated character bytes
  }
}

Please let me know if there are any functions that you don't understand as those functions have been tested to work up to the specification so far, hence why I didn't include them b/c they are not the source of the problem.

You forgot to #include <stdio.h> and <stdlib.h>

// How would i use sprintf function to convert temp_res data into string format
// in resultant pointer temp_res_text?

You already have the answer in your first version:

Code:

n = sprintf(temp_res_text, "%u", temp_res);

BTW, don't cast the return type of malloc(). See the FAQ for why it's bad.

Elysia: What do you mean 5 chars is not enough to hold an uint? My uint would have at max 10 bits resolution.
cpjust: Thanks for your time on the casting issues. I copied the example code from cplusplus.com's explanation of malloc(). Also, stdio.h and stdlib.h are ignored on purpose in mikroC development suite, I think. Hence why I didn't include them.

Originally Posted by stanlvw

Elysia: What do you mean 5 chars is not enough to hold an uint? My uint would have at max 10 bits resolution.

In that case, an unsigned short is all you need; but even then the largest number (on most systems) is 65535, so you'd still need an extra byte to store the '\0' in the string.

Code:

     temp_res_text = (char *) malloc(5);        // allocate 5 character bytes
     
     // How would i use sprintf function to convert temp_res data into string format
     // in resultant pointer temp_res_text?

I should be asking to look into one of your header files and see who much the uint (It might have been defined somewhere there) takes in terms of memory. Make sure u allocate the right amount of space. Which MicroControl are you programming? The only problem with sprintf function is that, its up to the programmer to make sure that Dest string have enough memory to fit in your source informatoin. Perhaps you can use snprintf function to avoid more complications, something as follow

Code:

#define MAXSIZ  10

char *Dest, *Extra;
int Len;

Dest = malloc(sizeof(char) * MAXSIZ);

if(Dest = NULL)
{
   printf("Error: No enough memory\n");
   return 1;
}

if( ( Len = snprintf(Dest, MAXSIZ, "%u", temp_res) ) >= MAXSIZ )
{
    Extra = malloc( sizeof(char) * Len + 1 );
    
    if(Extra == NULL)
    {
       printf("Error: No enough memory\n");
       return 1;
    }
    free(Dest);
    snprintf( Dest = Extra, Len, "%u", temp_res );
}

ssharish

The biggest number that I'm going to get is 1024.

ssharish2005: uint is a typedef type that's an unsigned int, which I think it's 10-bit resolution. I'm programming on a PIC18F2620 microcontroller using mikroC.

Originally Posted by stanlvw

ssharish2005: uint is a typedef type that's an unsigned int, which I think it's 10-bit resolution. I'm programming on a PIC18F2620 microcontroller using mikroC.

Thats fine, do this

Code:

Dest = malloc(sizeof(char) * sizeof(uint) + 1 );

ssharish

Do I need to change anything else on Extra pointer?

Originally Posted by stanlvw

Do I need to change anything else on Extra pointer?

Perhaps YES, you will have to free Extra before you leave the If statment i suppose, otherwise it becomes a memory leak. Sorry

Code:

#define MAXSIZ  sizeof(uint) 

char *Dest, *Extra;
int Len;

Dest = malloc(sizeof(char) * MAXSIZE + 1 );

if(Dest = NULL)
{
   printf("Error: No enough memory\n");
   return 1;
}

if( ( Len = snprintf(Dest, MAXSIZ, "%u", temp_res) ) >= MAXSIZ )
{
    Extra = malloc( sizeof(char) * Len + 1 );
    
    if(Extra == NULL)
    {
       printf("Error: No enough memory\n");
       return 1;
    }
    free(Dest);
    snprintf( Dest = Extra, Len, "%u", temp_res );
    free(Extra);
}

ssharish

It appears that malloc isn't supported in mikroC built-in. I guess it's a hardware related problem with respect to memory allocation. I guess I would have to try my luck on their forums.

i should have asked what compiler are using before?. And perharps you could cross compile the library to support the target board. I program Intel PXA255 series, my vendore gave me all cross compiled library along with board. Perhaps contact vendor and see if u get one. Or you can compile it by your self.

ssharish

I am using mikroC compiler on Microchip PIC18F series microcontroller. I have contacted the vendor mikroelektronika about it already. In the meanwhile, I'm trying to implement the source code of those missing functions.

I'm trying to implement the source code of those missing functions.

Do u mean malloc and free?

ssharish