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Pete Smith
Joined: 17 Sep 2003
Posts: 55
Location: Chester, UK
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| Strange "issue" with function prototypes |
 Posted: Fri Jan 23, 2004 4:15 am |
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Hi all.
Spent an amusing day yesterday tracking down an issue in my code. Compiler version is PCM 3.169.
The sensor I'm working on has FRAM, MMC card, digital I/O and analogue inputs, X10, LCD port etc etc, and a programming/control port.
This port uses commands like
R00000001<cr>
to read the PIC EEPROM location 0.
It wouldn't read above address 000000FF though.
Each function in itself worked. The string was passed to one function, to be parsed, which worked, then to an htoi32, which worked, and returned the value, but at the other end it didn't get through, only as an 8 bit number.
I finally tracked the problem down to the fact that my function prototype was declaring it as
int scan_string...
but it was actually
unsigned in32 scan_string...
Normally, the compiler will complain about function definitions and prototypes being different, but not in this case.
Just FYI!
Pete. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Jan 23, 2004 2:45 pm |
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I tested your problem with the latest version of PCM, 3.184,
and found the same problem. The compiler only looks at
the data size specified in the function prototype, and puts
in ASM code based on that. It ignores the return value
size that's specified in the actual function declaration.
In the case below, it only returns an 8-bi value. The
compiler doesn't give an error message about this, even
if +EW is added to the compiler options.
This is the ASM code produced if the function prototype
specifies an "int" as the return value.
| Code: | 0000 00314 .................... return(retval);
0010 0830 00315 MOVF 30,W
0011 00F8 00316 MOVWF 78 |
This is the ASM code produced if the function prototype
specifies an "int32" as the return value.
| Code: | 0000 00317 .................... return(retval);
0010 0830 00318 MOVF 30,W
0011 00F7 00319 MOVWF 77
0012 0831 00320 MOVF 31,W
0013 00F8 00321 MOVWF 78
0014 0832 00322 MOVF 32,W
0015 00F9 00323 MOVWF 79
0016 0833 00324 MOVF 33,W
0017 00FA 00325 MOVWF 7A |
In both cases, the actual function declaration is specified
to return an "int32".
If I compile a similar program in MSVC++ (substituting "long"
for "int32"), it gives this warning:
c:\msvc\test\test.c(23) : error C2371: 'scan_string' : redefinition; different basic types.
CL returned error code 2.
CCS should do that, too. You should report this to CCS.
#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)
int scan_string(char *ptr);
//==========================================
void main(void)
{
int32 value;
char buffer[10];
value = scan_string(buffer);
while(1);
}
//============================================
int32 scan_string(char *ptr)
{
int32 retval;
char c;
c = *ptr;
retval = 0x12345678;
return(retval);
} |
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Pete Smith
Joined: 17 Sep 2003
Posts: 55
Location: Chester, UK
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| Posted: Sun Jan 25, 2004 5:19 am |
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| PCM programmer wrote: |
If I compile a similar program in MSVC++ (substituting "long"
for "int32"), it gives this warning:
c:\msvc\test\test.c(23) : error C2371: 'scan_string' : redefinition; different basic types.
CL returned error code 2.
CCS should do that, too. You should report this to CCS.
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Thanks, I'll do that!
Pete. |
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