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Pointer use in function arguments

 
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Pointer use in function arguments
PostPosted: Sun Jul 29, 2007 3:15 pm     Reply with quote
Hello,

Assume that I have the following type description :

Code:
typedef struct _NETWORK_DATA {
   int8 IP[4];
   int8 MAC[6];
   int8 GATEWAY[4];
   int8 MASK[4];   
} NETWORK_DATA;


And that I use a pointer to this type as an argument for a function. How should I use the pointer to modify the content of the received data ? In the following example, only the first assignation works. Is it the normal C behavior ? I thought that these two notations should be equivalent.

Code:
void NovramGetNetworkData ( NETWORK_DATA * DATA ) {
   DATA->MAC[0] = 101;
   (*DATA).MAC[1] = 102; 
}


Note.:
System : WinXP
PCWH V4.047

For info, here is the generated assembler :
Code:
....................    DATA->MAC[0] = 101;
*
00398:  MOVLW  04
0039A:  ADDWF  34,W
0039C:  MOVWF  FE9
0039E:  MOVLW  00
003A0:  ADDWFC 35,W
003A2:  MOVWF  FEA
003A4:  MOVLW  65
003A6:  MOVWF  FEF
....................    (*DATA).MAC[1] = 102;
003A8:  MOVLW  05
003AA:  MOVWF  FE9
003AC:  CLRF   FEA
003AE:  MOVLW  66
003B0:  MOVWF  FEF



Dimitri
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Sun Jul 29, 2007 3:59 pm     Reply with quote
I installed PCH vs. 4.047, compiled the test program shown below,
and ran it in MPLAB simulator (vs. 7.41). It worked fine.
Here's the output of the program.
Quote:
101, 102


Here's the ASM code for the two lines. It looks the same.
Code:

....  DATA->MAC[0] = 101; 
0004:  MOVLW  04
0006:  ADDWF  18,W
0008:  MOVWF  FE9
000A:  MOVLW  00
000C:  ADDWFC 19,W
000E:  MOVWF  FEA
0010:  MOVLW  65
0012:  MOVWF  FEF
....  (*DATA).MAC[1] = 102;   
0014:  MOVLW  05
0016:  ADDWF  18,W
0018:  MOVWF  FE9
001A:  MOVLW  00
001C:  ADDWFC 19,W
001E:  MOVWF  FEA
0020:  MOVLW  66
0022:  MOVWF  FEF
.................... 


Here's the test program. I used your code and just added
the necessary things to make a test program.
Code:

#include <18F452.h>
#fuses XT,NOWDT,NOPROTECT,BROWNOUT,PUT,NOLVP
#use delay(clock=4000000) 
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)

typedef struct _NETWORK_DATA {
   int8 IP[4];
   int8 MAC[6];
   int8 GATEWAY[4];
   int8 MASK[4];   
} NETWORK_DATA;


void NovramGetNetworkData ( NETWORK_DATA * DATA )
{
 DATA->MAC[0] = 101;
 (*DATA).MAC[1] = 102; 

}

//=======================
void main()
{
NETWORK_DATA DATA;

NovramGetNetworkData(&DATA); 

printf("%u, %u \n\r", DATA.MAC[0], DATA.MAC[1]);

while(1);
}
Guest
PostPosted: Sun Jul 29, 2007 5:07 pm     Reply with quote
Thank you for the answer.

I made some more tests ( reducing my program until the code is correct ) and I found that the error comes from the fact that I used the magical option 'multiple compilation units' together with the 'link separately'

If I force all the sources into one file by including the '.c' files instead of the '.h' files and make a project without the multiple compilation units, the code is correctly generated.

I think I will report a bug on that point.

This is the test program to compile with the magical option :
Main file :
Code:
#include "global.h"
typedef struct _NETWORK_DATA {                               
   int8 IP[4];
   int8 MAC[6];
   int8 GATEWAY[4];
   int8 MASK[4];   
} NETWORK_DATA;
 
void NovramGetNetworkData ( NETWORK_DATA * DATA ) {
   (*DATA).MAC[0] = 105;
   DATA->MAC[0] = 105;
} 

void main(void) {     
   NETWORK_DATA NET_DATA;
   NovramGetNetworkData ( &NET_DATA );
   while(TRUE) {
   }
}


Separate file (.h):
Code:
#ifndef GLOBAL__H
#define GLOBAL__H
   #include <18F4620.h>                                 
   #device *=16
   #fuses H4, NOWDT, NOLVP, NODEBUG
   #use delay(clock=40000000)       
   #use rs232(baud=19200, xmit=PIN_C6, rcv=PIN_C7)
     
   void InitUserIO ( void );
#endif 


Separate file (.c):
Code:
#include "global.h"
void InitUserIO ( void ) {
   *0xF92 = 0xDF;                      // PortA : A5 output, A4..A0 input   
   *0xF93 = *0xF93 & 0xCF;             // PortB : B5..B4 output     
   *0xF94 = *0xF94 & 0xF8;             // PortC : C2..C0 output
   *0xF95 = *0xF95 & 0xFB;             // PortD : D2 output
}
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