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Pointer/Function help

So, I am trying to put together two (rather involved) functions that calculate the DAC. My processing routine for CalcDAC1 and CalcDAC2 are more or less the same, but with different variables. Currently, I'm using global variables that are directly called from the routine. I would like to use the same functionality but send it the variables I want the program to use to process so instead of:

global variables:
unsigned int var1a;
unsigned int var2a;
unsigned int var3a;
unsigned int var1b;
unsigned int var2b;
unsigned int var3b;

void main(void)
{

     while(1)
     {
          CalcDAC1();
          CalcDAC2();
     }
}

void CalcDAC1(void)
{

//Do stuff with var1a
//Do stuff with var2a
//Do stuff with var3a

}

Void CalcDAC2(void)
{

//Do stuff with var1b
//Do stuff with var2b
//Do stuff with var3b

}

I instead would like to do

void main(void)
{

     while(1)
     {
          CalcDAC(var1a, var2a, var3a);
          CalcDAC(var1b, var2b, var3b);
     }
}

void CalcDAC(unsigned char var1, unsigned char var2, unsigned char var3)
{

     //Do stuff with var1
     //Do stuff with var2
     //Do stuff with var3

}

Unfortunately, my particular function has about 7-10 variables (complicated equation with lots of variables) so it requires me to create a LOT of local variables for each iteration, which I don't have the local space for (if that's the right term). Instead, I would like to send it pointers to local variables (if possible).

I ASSUME it would look something like this:

void main(void)
{

     while(1)
     {
          CalcDAC(*var1a, *var2a, *var3a);
          CalcDAC(*var1b, *var2b, *var3b);
     }
}

void CalcDAC(unsigned char *var1, unsigned char *var2, unsigned char *var3)
{

     //Do stuff with var1
     //Do stuff with var2
     //Do stuff with var3

}

Is this correct or is this even possible in C? Is this something you can only do in C++? Any help with implementation you can give me would be greatly appreciated. Thanks!

Parents

0 ImPer Westermark over 13 years ago in reply to Jeremy Brookley

struct {
    int a;
    int b;
} my_struct_variable;    // <= this is a variable.

struct my_struct_type {  // <= this is a data type - not a variable.
    int a;
    int b;
};

struct my_struct_type a_variable;  // <= create a variable of this type.

typedef struct {
    int a;
    int b;
} my_struct_type2;  // <= also a data type.

my_struct_type2 settings_1,settings_2;  // <= two variables of this custom type.

int my_special_function(my_struct_type2* settings) {
    return settings->a + settings->b;   // now have a pointer to a struct, so -> for pointer indirection.
}

void main(void) {
    settings_1.a = 1;  // <= my_struct_variable is not a pointer, so no ->.
    settings_1.b = 1;
    my_special_function(&settings_1);
    settings_2.a = 2;
    settings_2.b = 3;
    my_special_function(&settings_2);
    for (;;) ;
}

Reply

0 ImPer Westermark over 13 years ago in reply to Jeremy Brookley

struct {
    int a;
    int b;
} my_struct_variable;    // <= this is a variable.

struct my_struct_type {  // <= this is a data type - not a variable.
    int a;
    int b;
};

struct my_struct_type a_variable;  // <= create a variable of this type.

typedef struct {
    int a;
    int b;
} my_struct_type2;  // <= also a data type.

my_struct_type2 settings_1,settings_2;  // <= two variables of this custom type.

int my_special_function(my_struct_type2* settings) {
    return settings->a + settings->b;   // now have a pointer to a struct, so -> for pointer indirection.
}

void main(void) {
    settings_1.a = 1;  // <= my_struct_variable is not a pointer, so no ->.
    settings_1.b = 1;
    my_special_function(&settings_1);
    settings_2.a = 2;
    settings_2.b = 3;
    my_special_function(&settings_2);
    for (;;) ;
}

Children

0 Jeremy Brookley over 13 years ago in reply to ImPer Westermark

So for my example, this is what it would look like:

typedef struct // I'm creating a data type here
{
        signed short var1;
        signed short var2;
        signed short var3;
} DACStruct;

DACStruct idata DACStructVar; // I'm creating a variable based on the DACStruct here.  This will create it in the idata register 

void main(void)
{

     DACStructVar.var1 = 1;
     DACStructVar.var2 = 2;
     DACStructVar.var3 = 3;

     CalcDAC(&DACStructVar); // Should I be using a pointer here or should I be directly calling DACStructVar here?
}

void CalcDAC(DACStruct idata* MyDACStruct) // Did I want a pointer here? 
{

// do stuff with struct here

}

Am I using the idata sections correctly? Did I want to use pointers with this or should I be directly calling the DACStructVar in the CalcDAC routine (DACStruct or &DACStruct)? Thanks for your help, I think I'm getting closer now!