C Array Initialization getting error

Question

I have tried to define a 2 dimension array in c language and initialize it with variables of float types but I have got this error:

"must be constant expression"
here is my code:

/*******************************************************
This program was created by the
CodeWizardAVR V3.12 Advanced
Automatic Program Generator
© Copyright 1998-2014 Pavel Haiduc, HP InfoTech s.r.l.
http://www.hpinfotech.com

Project : 
Version : 
Date    : 1/30/2017
Author  : 
Company : 
Comments: 


Chip type               : ATmega8A
Program type            : Application
AVR Core Clock frequency: 8.000000 MHz
Memory model            : Small
External RAM size       : 0
Data Stack size         : 256
*******************************************************/

#include <mega8.h>
#include <stdio.h>
#include <delay.h>
#include <alcd.h>

#define A Hall_1
#define B Hall_2
#define C Hall_3


//...........................................................................................
// Declare your global variables here
float Hall_1 ,Hall_2 ,Hall_3 ;
int count=0;

//----------------------------------------------------------------------------------------------------

// Timer 0 overflow interrupt service routine
interrupt [TIM1_OVF] void timer1_ovf_isr(void)
{
count++;

}

//----------------------------------------------------------------------------------------------

// ADC interrupt service routine
interrupt [ADC_INT] void adc_isr(void)
{


}
//-----------------------------------------------------------------------------------------------

float adc_read(unsigned char);
float maxf(float , float , float);
float minf(float , float , float);
void commutate(unsigned char*);

//-----------------------------------------------------------------------------------------------

void main(void)
{
// Declare your local variables here

float comt_sequence[6][2]= {{B,A},{B,C},{A,C},{A,B},{C,B},{C,A}};
// Timer/Counter 0 initialization
// Clock source: System Clock
// Clock value: 8000.000 kHz
TCCR1B=(0<<CS02) | (0<<CS01) | (0<<CS00);
TCNT1=0x00;



// Timer(s)/Counter(s) Interrupt(s) initialization
TIMSK=(0<<OCIE2) | (0<<TOIE2) | (0<<TICIE1) | (0<<OCIE1A) | (0<<OCIE1B) | (0<<TOIE1) | (0<<TOIE0);

// External Interrupt(s) initialization
// INT0: Off
// INT1: Off
MCUCR=(0<<ISC11) | (0<<ISC10) | (0<<ISC01) | (0<<ISC00);


// ADC initialization
// ADC Clock frequency: 250.000 kHz
// ADC Voltage Reference: Int., cap. on AREF
// Only the 8 most significant bits of
// the AD conversion result are used
ADMUX= (1<<REFS1) | (1<<REFS0) | (1<<ADLAR) ;
ADCSRA=(1<<ADEN) | (0<<ADSC) | (0<<ADFR) | (0<<ADIF) | (0<<ADIE) | (1<<ADPS2) | (0<<ADPS1) | (1<<ADPS0);
SFIOR=(0<<ACME);

// Alphanumeric LCD initialization
// Connections are specified in the
// Project|Configure|C Compiler|Libraries|Alphanumeric LCD menu:
// RS - PORTD Bit 0
// RD - PORTD Bit 1
// EN - PORTD Bit 2
// D4 - PORTD Bit 4
// D5 - PORTB Bit 6
// D6 - PORTB Bit 7
// D7 - PORTD Bit 5
// Characters/line: 16
lcd_init(40);

// Global enable interrupts
#asm("sei")

lcd_putsf("start");
delay_ms(500);
lcd_clear();

while (1)
      { 

       unsigned char buffer[18] , s=0;
       float m,n=0 , max_min[2]; 
       TCCR1B=1; //start counting cycles
       Hall_1 = adc_read(5);
       Hall_2 = adc_read(4);
       Hall_3 = adc_read(3);

       m=maxf(Hall_1,Hall_2,Hall_3); 
       /*if(m == Hall_1) 
                    lcd_putsf("Max= A ");  
       else if(m == Hall_2)
                    lcd_putsf("Max= B ");
       else if(m == Hall_3)
                    lcd_putsf("Max= C ");
       else
            lcd_putsf("Error"); */

       n=minf(Hall_1,Hall_2,Hall_3);
       /*if(n == Hall_1) 
                    lcd_putsf("Min= A");  
       else if(n == Hall_2)
                    lcd_putsf("Min= B");
       else if(n == Hall_3)
                    lcd_putsf("Min= C");
       else
            lcd_putsf("Error");*/
       max_min[0] = m;
       max_min[1] = n;  

       s=count;
       sprintf(buffer,"%5.4f %5.4f %d",max_min[0],max_min[1] ,TCNT1);
       lcd_puts(buffer);    
       delay_ms(1000);
       lcd_clear();
      }
}



///////////////////////////////////////////////
float adc_read(unsigned char ch)
{

    unsigned char lcd_buff[18];
    float adc_data;
  // select the corresponding channel 0~7
  // ANDing with ’7' will always keep the value
  // of ‘ch’ between 0 and 5   ""ATmega8 has 6 ADC channel 0-5""
  ch &= 0b00000111;  // AND operation with 5
  ADMUX = (ADMUX & 0xF8)|ch; // clears the bottom 3 bits before ORing   

  // start single convertion
  // write ’1' to ADSC
  ADCSRA |= (1<<ADSC);

    // Wait for the AD conversion to complete
    while ((ADCSRA & 0x10)==0);
    ADCSRA|=0x10;

    // Read the 8 most significant bits
    // of the AD conversion result
    adc_data=(ADCH * 2.56)/255;
    //sprintf(lcd_buff," %5.3f ",adc_data);
    //lcd_puts(lcd_buff);
    //delay_ms(500);
    return adc_data;
}

//------------------------------------------------------------------------------------------------
float maxf(float a , float b , float c) {

float m;
m = (a>b)?a:b;
m = (m>c)?m:c;
return m;
}

float minf(float a , float b , float c) {

float m;
m = (a<b)?a:b;
m = (m<c)?m:c;
return m;
}

//--------------------------------------------------------------------------------------
void commutate(unsigned char *max_min){

unsigned char x=0, i=0;


//unsigned char comt_pattern[6][2] = {(
for (i=0; i<6 ;i++)
    if((max_min[0] == comt_sequence[i][0]) && (max_min[1] == comt_sequence[i][1])) x=i;
switch(x){
    case 0:
    break;
    case 1:
    break;
    case 2:
    break;
    case 3:
    break;
    case 4:
    break;
    case 5:
    break;
    }

}

i add my whole code also i mention that Hall variables holds an ADC reading from a sensor and its values changes periodically what is my fault?
please help

that's because `Hall_1 ,Hall_2 ,Hall_3` are not constant (and not initialized BTW). — Jean-François Fabre, Feb 01 '17 at 10:30
Possible duplicate of [Error "initializer element is not constant" when trying to initialize variable with const](http://stackoverflow.com/questions/3025050/error-initializer-element-is-not-constant-when-trying-to-initialize-variable-w) — P.P, Feb 01 '17 at 10:34

Vlad from Moscow · Answer 1 · 2017-02-01T10:39:25.267

1

You may not initialize arrays in C with static storage duration with non-constant initializers.

From the C Standard (6.7.9 Initialization)

4 All the expressions in an initializer for an object that has static or thread storage duration shall be constant expressions or string literals.

It seems your array is declared outside any function. If it is possible declare it in a function for example in main.

edited Feb 01 '17 at 10:39

answered Feb 01 '17 at 10:33

Vlad from Moscow

301,070
26
186
335

So what can i do instead of defining an array to hold {B,A},{B,C},{A,C},{A,B},{C,B},{C,A} how can i use macros instead of arrays? – Kamaran Hussini Feb 01 '17 at 10:45
1

@KamaranHussini Define it inside main that it had automatic storage duration. – Vlad from Moscow Feb 01 '17 at 10:46
Does Arrays just can hold constant array? so it means the whole my initialization of Array is error?! is it not possible to array to hold variables? – Kamaran Hussini Feb 01 '17 at 10:53
@KamaranHussini The variables Hall_1and and so on also should be initialized with constant expressions. – Vlad from Moscow Feb 01 '17 at 10:53
I changed code as follow and it works now: void commutate(unsigned char *max_min){ unsigned char X=0, i=0; float* comt_sequence[6][2]= { (&Hall_2,&Hall_1) , (&Hall_2,&Hall_3), (&Hall_1,&Hall_3) , (&Hall_1,&Hall_2), (&Hall_3,&Hall_2) , (&Hall_3,&Hall_1) }; for (i=0; i<6 ;i++){ if( (max_min[0] == (*comt_sequence[i][0])) && (max_min[1] == (*comt_sequence[i][1]))) X=i;} – Kamaran Hussini Feb 01 '17 at 19:33

msc · Answer 2 · 2017-02-01T10:54:25.037

0

When creating an array like that, its size must be constant, because C doesn't allow non-constant values for the size of an array.

C99 standard section 6.7.8 (Initialization), point 4:

All the expressions in an initializer for an object that has static storage duration shall be constant expressions or string literals.

I did changes your code. try it.

#include <stdio.h>

#define Hall_1 10
#define Hall_2 20
#define Hall_3 30   

int main() 
{       
float  A,B,C;

A = Hall_1;
B = Hall_2; 
C = Hall_3;

float commutate_sequence[6][2]= {{B,A},{B,C},{A,C},{A,B},{C,B},{C,A}};
    return 0;
}

edited Feb 01 '17 at 10:54

answered Feb 01 '17 at 10:31

msc

33,420
29
119
214

3

They are not array sizes, though. The sizes, `6` and `2`, are very constant. – molbdnilo Feb 01 '17 at 10:32
Hall_1 and so on have contents that changes periodically they have not constant values . – Kamaran Hussini Feb 01 '17 at 11:20

score 0 · Answer 3 · answered Feb 02 '17 at 10:56

I changed code as follow and it works now:

#define A Hall_1
#define B Hall_2
#define C Hall_3
void commutate(unsigned char max_min)
{ unsigned char X=0, i=0; 
float comt_sequence[6][2]= { (&Hall_2,&Hall_1) , (&Hall_2,&Hall_3),(Hall_1,&Hall_3) ,  (&Hall_1,&Hall_2),                                                             &Hall_3,&Hall_2) , (&Hall_3,&Hall_1) };
for (i=0; i<6 ;i++)
{ if( (max_min[0] == (*comt_sequence[i][0])) && (max_min[1] == (*comt_sequence[i][1]))) X=i;}

C Array Initialization getting error

3 Answers3