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Problem with struct pointer, cannot access character array

 
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Franco
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Problem with struct pointer, cannot access character array
PostPosted: Wed May 26, 2004 12:32 am     Reply with quote

Hello,

I have definded the following struct and a pointer to this struct:

Code:
struct mystruct {
  int myfirstint;
  char myarray[10];
  int mylastint;
} thisismystruct;

struct mystruct *mystructPtr;
.....
.....

Now I point the struct pointer to this struct and I want to access the struct elements using the struct pointer operator -> :

Code:
mystructPtr = &thisismystruct;

mystructPtr->myfirstint;             // works fine, returns the correct value
mystructPtr->myarray[0];             // does not work, returns wrong value
mystructPtr->myarray[5];             // does not work, returns wrong value
mystructPtr->mylastint;              // works fine, returns the correct value


This works fine for the integers, but if I want to access the elements of the character array, I get completely wrong values. I had a look at the generated assembler code, and it looks wrong for the character array, because it seems to simple.

Does anyone out there have an idea?

Cheers Franco
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Wed May 26, 2004 10:32 am     Reply with quote

I made a test program, to check your problem.
It works fine with a 16F877, and PCM vs. 3.188.

The output on my terminal window is: A05B

Code:
#include <16F877.h>
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock = 4000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)

struct mystruct {
  int myfirstint;
  char myarray[10];
  int mylastint;
} thisismystruct;

struct mystruct *mystructPtr;

//===========================================
void main(void)
{
char c;
char i;

//--------
// Initialize the structure.

thisismystruct.myfirstint = 'A';

// Fill the array with ASCII chars '0' to '9'.
for(i = 0; i < 10; i++)
   {
    thisismystruct.myarray[i] = i + '0';
   }

thisismystruct.mylastint = 'B';

//-------
// Display some elements of the structure.

mystructPtr = &thisismystruct;

c = mystructPtr->myfirstint; 
putc(c);
c = mystructPtr->myarray[0]; 
putc(c);
c = mystructPtr->myarray[5]; 
putc(c);
c = mystructPtr->mylastint;   
putc(c);

while(1);
}
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