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Hi all,
I've this strange problem with the \0 character. I'll show you the code first:
#include <REG52.H> void test(char *s) { int idx; for(idx = 0; *s != '\0'; idx++, s++) { } P1 = idx; // Led's are connected to P1 so i can see the idx value. } void main() { test("12345"); while(1); }
Now the problem: When i call the test function with 4 characters or less, the condition
*s != '\0'
does not work. The led's show me a value of 0x63 when i call the test function with 1, 2, 3 or 4 characters. There's no problem when i call the test function with 5 characters or more. The led's show me 0x05 with a call of 5 characters.
I've also tested this code with the SDCC compiler and the call with 4 characters or less did worked like it should.
I'm working with the C51 COMPILER V8.05a
Any ideas? Thanks!
Here's another idea. Since your function is basically strlen, why don't you do the following:
P1 = strlen ("123");
and see if that fails. If it does, then we KNOW that there is some kind of hardware issue and not a compiler problem.
Jon
As it appears to have a compiler dependance, I'm suspicious that it might be an optimisation problem. Have you tried turning optimisation off?
I guess you didn't see my post that I tried M. Swiebertje's code (as posted) with the same compiler and it runs fine here. Also, M. Swiebertje reports that it runs fine in the Keil simulator. I really doubt that the simulator simulates it correctly but the hardware does not.
However, without knowing the following...
...it's impossible to accurately GUESS what's going on.
However, based on all the evidence provided, it does not appear to be a problem with the compiler.
Since it is possible to see the code generated by the Keil compiler, I would think that a true engineer would at least glance at that to see if it looks OK or not (maybe I'm wrong). Also, based on the trivality of the code, I would also assume that commentators would at least try to run it and see what the results were before making wild speculation. It took me less than 5 minutes to compile and test the example provided.
Following is the generated code for a test string of 3 characters:
C51 COMPILER V8.05a, COMPILATION OF MODULE MAIN OBJECT MODULE PLACED IN main.OBJ COMPILER INVOKED BY: C:\Keil\C51\BIN\C51.EXE main.c DEBUG OBJECTEXTEND CODE SYMBOLS 1 #include 2 3 void test(char *s) 4 { 5 1 int idx; 6 1 7 1 for(idx = 0; *s != '\0'; idx++, s++) 8 1 { 9 2 } 10 1 11 1 P1 = idx; // Led's are connected to P1 so i can see the idx value. 12 1 } 13 14 void main() 15 { 16 1 test("123"); 17 1 18 1 while(1); 19 1 } ASSEMBLY LISTING OF GENERATED OBJECT CODE ; FUNCTION _test (BEGIN) ; SOURCE LINE # 3 ;---- Variable 's' assigned to Register 'R1/R2/R3' ---- ; SOURCE LINE # 4 ; SOURCE LINE # 7 ;---- Variable 'idx' assigned to Register 'R6/R7' ---- 0000 E4 CLR A 0001 FF MOV R7,A 0002 FE MOV R6,A 0003 ?C0001: 0003 120000 E LCALL ?C?CLDPTR 0006 600E JZ ?C0002 ; SOURCE LINE # 8 ; SOURCE LINE # 9 0008 0F INC R7 0009 BF0001 CJNE R7,#00H,?C0008 000C 0E INC R6 000D ?C0008: 000D 7401 MOV A,#01H 000F 29 ADD A,R1 0010 F9 MOV R1,A 0011 E4 CLR A 0012 3A ADDC A,R2 0013 FA MOV R2,A 0014 80ED SJMP ?C0001 0016 ?C0002: ; SOURCE LINE # 11 0016 8F90 MOV P1,R7 ; SOURCE LINE # 12 0018 22 RET ; FUNCTION _test (END) ; FUNCTION main (BEGIN) ; SOURCE LINE # 14 ; SOURCE LINE # 15 ; SOURCE LINE # 16 0000 7BFF MOV R3,#0FFH 0002 7A00 R MOV R2,#HIGH ?SC_0 0004 7900 R MOV R1,#LOW ?SC_0 0006 120000 R LCALL _test 0009 ?C0005: ; SOURCE LINE # 18 0009 80FE SJMP ?C0005 ; FUNCTION main (END)
And following is the code for a test string of 5 characters:
C51 COMPILER V8.05a, COMPILATION OF MODULE MAIN OBJECT MODULE PLACED IN main.OBJ COMPILER INVOKED BY: C:\Keil\C51\BIN\C51.EXE main.c DEBUG OBJECTEXTEND CODE SYMBOLS line level source 1 #include 2 3 void test(char *s) 4 { 5 1 int idx; 6 1 7 1 for(idx = 0; *s != '\0'; idx++, s++) 8 1 { 9 2 } 10 1 11 1 P1 = idx; // Led's are connected to P1 so i can see the idx value. 12 1 } 13 14 void main() 15 { 16 1 test("12345"); 17 1 18 1 while(1); 19 1 } ASSEMBLY LISTING OF GENERATED OBJECT CODE ; FUNCTION _test (BEGIN) ; SOURCE LINE # 3 ;---- Variable 's' assigned to Register 'R1/R2/R3' ---- ; SOURCE LINE # 4 ; SOURCE LINE # 7 ;---- Variable 'idx' assigned to Register 'R6/R7' ---- 0000 E4 CLR A 0001 FF MOV R7,A 0002 FE MOV R6,A 0003 ?C0001: 0003 120000 E LCALL ?C?CLDPTR 0006 600E JZ ?C0002 ; SOURCE LINE # 8 ; SOURCE LINE # 9 0008 0F INC R7 0009 BF0001 CJNE R7,#00H,?C0008 000C 0E INC R6 000D ?C0008: 000D 7401 MOV A,#01H 000F 29 ADD A,R1 0010 F9 MOV R1,A 0011 E4 CLR A 0012 3A ADDC A,R2 0013 FA MOV R2,A 0014 80ED SJMP ?C0001 0016 ?C0002: ; SOURCE LINE # 11 0016 8F90 MOV P1,R7 ; SOURCE LINE # 12 0018 22 RET ; FUNCTION _test (END) ; FUNCTION main (BEGIN) ; SOURCE LINE # 14 ; SOURCE LINE # 15 ; SOURCE LINE # 16 0000 7BFF MOV R3,#0FFH 0002 7A00 R MOV R2,#HIGH ?SC_0 0004 7900 R MOV R1,#LOW ?SC_0 0006 120000 R LCALL _test 0009 ?C0005: ; SOURCE LINE # 18 0009 80FE SJMP ?C0005 ; FUNCTION main (END)
Careful comparison between the test function will show that they are identical.
So, if it works with 5 characters or more but fails for 4 characters or less, the problem would not appear to come from the generated code.