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hmmpic
Joined: 09 Mar 2010
Posts: 314
Location: Denmark
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| Pointer confused |
 Posted: Tue Mar 04, 2014 1:20 pm |
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Small example, for pointer to string confusion?
What I want to ask is the generated asm code, it it real different?
Compiler:5020.
EX1 Code:
| Code: | #include <18F26K22.h>
/*Only test program, not for production in PIC*/
char *ptr;//Pointer to a pre. defined string -> String = 0123456789;
void Test(){
char tmp;
tmp= *ptr; //is this '0'
tmp= ptr[0]; //is this '0'
tmp= *(ptr+1);//is this '1'
tmp= ptr[1]; //is this '1'
}
void main(){
Test();
} |
EX1 Out: | Code: |
.................... void Test(){
.................... char tmp;
.................... tmp= *ptr; //is this '0'
00004: MOVFF ptr,FSR0L
00008: MOVFF ptr+1,FSR0H
0000C: MOVFF INDF0,tmp
.................... tmp= ptr[0]; //is this '0'
00010: MOVFF ptr,FSR0L
00014: MOVFF ptr+1,FSR0H
00018: MOVFF INDF0,tmp
....................
.................... tmp= *(ptr+1);//is this '1'
0001C: MOVLW 01
0001E: ADDWF ptr,W
00020: MOVWF @01
00022: MOVLW 00
00024: ADDWFC ptr+1,W
00026: MOVFF 01,FSR0L
0002A: MOVWF FSR0H
0002C: MOVFF INDF0,tmp
.................... tmp= ptr[1]; //is this '1'
00030: MOVLW 01
00032: ADDWF ptr,W
00034: MOVWF FSR0L
00036: MOVLW 00
00038: ADDWFC ptr+1,W
0003A: MOVWF FSR0H
0003C: MOVFF INDF0,tmp
00040: GOTO 0062 (RETURN)
.................... } |
***
EX2 Code:
| Code: | #include <18F26K22.h>
/*Only test program, not for production in PIC*/
char *ptr[2];//Pointer array to a pre. defined string -> String = 0123456789;
void Test(){
char tmp;
tmp= *(ptr[0]); //is this '0'
tmp= ptr[0][0]; //is this '0'
tmp= *(ptr[0]+1); //is this '1'
tmp= ptr[0][1]; //is this '1'
}
void main(){
Test();
}
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Ex2 Out:
| Code: |
.................... void Test(){
.................... char tmp;
.................... tmp= *(ptr[0]); //is this '0'
00004: MOVFF ptr,FSR0L
00008: MOVFF ptr+1,FSR0H
0000C: MOVFF INDF0,tmp
.................... tmp= ptr[0][0]; //is this '0'
00010: MOVFF ptr,tmp
....................
.................... tmp= *(ptr[0]+1);//is this '1'
00014: MOVLW 01
00016: ADDWF ptr,W
00018: MOVWF @01
0001A: MOVLW 00
0001C: ADDWFC ptr+1,W
0001E: MOVFF 01,FSR0L
00022: MOVWF FSR0H
00024: MOVFF INDF0,tmp
.................... tmp= ptr[0][1]; //is this '1'
00028: MOVFF ptr+1,tmp
0002C: GOTO 004E (RETURN)
.................... } |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19477
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| Posted: Wed Mar 05, 2014 1:52 am |
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A search here will find quite a bit about this.
Report it to CCS.
Problems with multi-dimensional pointer arrays have been common. They tend to come and go with versions.
In the past I have suggested deliberate casting as the most reliable way of avoiding problems. So explicitly storing the pointers as int16, and then casting them to 'char *' on retrieval.
It had been fixed a few versions ago.
As you have found, there is only a problem when they are used/stored as *ptr[], not as ptr[][].
Just 'FYI', realise that as posted, the compiler _pre solves_ the location of ptr[0][0] (for example), to access the data stored there, rather than using the indirect access when the pointer is used.
Worth posting your test example, so we can see the pointers are correctly loaded:
| Code: |
void main(){
char data[]="0123456789";
ptr[0]=data;
ptr[1]=data;
Test2();
while(TRUE);
}
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For example.
Best Wishes |
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hmmpic
Joined: 09 Mar 2010
Posts: 314
Location: Denmark
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| Posted: Fri Apr 18, 2014 6:56 am |
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Hi
Just to inform that CCS have fixed the issue. It will be in next release:-) |
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