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passing a struct through one function into another

 
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rwjzownts



Joined: 19 Jul 2008
Posts: 16

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passing a struct through one function into another
PostPosted: Tue Sep 30, 2008 5:28 pm     Reply with quote
I would like to pass a struct into one function that will then pass the same struct into another function. Is this possible? I haven't been able to find anything about doing this. Here's my falied attempt:

In main:

Code:
      if(servo0.counter > servo0.trigger)
      {
         //ledBlink(&servo0);
         whichServo(&servo0);
      }
      if(servo1.counter > servo1.trigger)
      {
         //ledBlink(&servo1);
         whichServo(&servo1);
      }


First function:
Code:
void whichServo(servoStruct *structIn)
{
   if(structIn->led == 0)
   {
      ledBlink(&structIn);
   }
}

Second function:
Code:
void ledBlink(servoStruct *structIn)
{
   if(structIn->led == 3)
   {
      output_toggle (PIN_C3);
   }
   else if(structIn->led == 4)
   {
      output_toggle (PIN_C4);
   }
   structIn->counter = 0;
}


Here's all the code:
Code:
#include <18F2620.h>
#FUSES HS
#FUSES NOWDT
#FUSES NOPROTECT
#use delay(clock=20,000,000)
#use rs232 (baud = 9600, parity = N, xmit = PIN_C6, rcv = PIN_C7, bits = 8, ERRORS)
#define RAND_MAX 1000
#include <STDLIB.H>

typedef struct{
   int16 counter;
   int16 trigger;
   int8 led;
}servoStruct;

servoStruct servo0;
servoStruct servo1;

void ledBlink(servoStruct *structIn);
void whichServo(servoStruct *structIn);

#INT_RTCC
void servocounter()
{
   servo0.counter++;
   servo1.counter++;
   set_timer0(60535);
}
   
void main()
{
   setup_comparator (NC_NC_NC_NC);
   setup_timer_0 (RTCC_DIV_1|RTCC_INTERNAL);
   enable_interrupts (INT_RTCC);
   enable_interrupts (GLOBAL);
     
   servo0.counter = 0;
   servo0.trigger = 1000;
   servo1.counter = 0;
   servo1.trigger = 500;
   servo0.led = 3;
   servo1.led = 4;
         
   delay_ms (500);
   output_high(PIN_C3);
   output_high(PIN_C4);

   WHILE (true)
   {
      if(servo0.counter > servo0.trigger)
      {
         //ledBlink(&servo0);
         whichServo(&servo0);
      }
      if(servo1.counter > servo1.trigger)
      {
         //ledBlink(&servo1);
         whichServo(&servo1);
      }
   }
}

void whichServo(servoStruct *structIn)
{
   if(structIn->led == 0)
   {
      ledBlink(&structIn);
   }
}

void ledBlink(servoStruct *structIn)
{
   if(structIn->led == 3)
   {
      output_toggle (PIN_C3);
   }
   else if(structIn->led == 4)
   {
      output_toggle (PIN_C4);
   }
   structIn->counter = 0;
}
Ttelmah
Guest
PostPosted: Wed Oct 01, 2008 5:18 am     Reply with quote
Perfectly possible.
The problem is that in the first function, "StructIn", is _already_ the address of the structure. You then take the address of _this_, and pass it to the second function.
Historically, it was suggested in C, that you use different nomenclature for pointers, to avoid making this mistake. So, if you call the variable in the first function (for example), ptr_to_StructIn, it becomes obvious when you go to pass it to the second, that it is already a pointer and you shouldn't use the '&'.

Best Wishes
rwjzownts



Joined: 19 Jul 2008
Posts: 16

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Thanks!
PostPosted: Wed Oct 01, 2008 3:18 pm     Reply with quote
That makes sense. I got it to work. Thanks!
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