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Join Date: Apr 2008

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paolomontero paolomontero is offline

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Tubo C strange problem

Jun 4th, 2008

Hi,

I'm using Turbo C 2.01 and im stuck with this problem.

I've reduced it to the following. My code in Turbo C is this:

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
void f(char *);
 
char h[] = "hello";
 
void main() {
	f(h);
}
 
void f(char *s) {
	int n = 0;
	while (s[n] != 0) {
		/*do something*/
		n++;
	}
}
void f(char *);

char h[] = "hello";

void main() {
	f(h);
}

void f(char *s) {
	int n = 0;
	while (s[n] != 0) {
		/*do something*/
		n++;
	}
}

It's just a function that takes a string as an argument and merely loops till it finds the terminating NULL character.

I compile it like this (the file is named c.c):

tcc -mt c.c
tlink C.OBJ

and then i do exe2bin C.EXE to get the raw binary image.

The disassembly for either the .bin or .exe (they are the same, but it's easier to work with the .bin because it doesn't have the "turbo c junk code") is the following:

 Help with Code Tags 
 ASM Syntax (Toggle Plain Text) 
0000	mov ax, 000E
0003	push ax
0004	call 0009
0007	pop cx
0008	ret
0009	push bp
000A	mov bp, sp
000C	push si
000D	xor si, si
000F	jmp 0012
0011	inc si
0012	mov bx, [bp+04]
0015	cmp byte ptr [bx+si], 00
0018	jne 0011
001A	pop si
001B	pop bp
001C	ret
001E	'hello\0' ;you get me :)
0000	mov ax, 000E
0003	push ax
0004	call 0009
0007	pop cx
0008	ret
0009	push bp
000A	mov bp, sp
000C	push si
000D	xor si, si
000F	jmp 0012
0011	inc si
0012	mov bx, [bp+04]
0015	cmp byte ptr [bx+si], 00
0018	jne 0011
001A	pop si
001B	pop bp
001C	ret
001E	'hello\0' ;you get me :)

So, the problem is the first line!

mov ax, 000E

It doesn't point to the string, which is located in 001E, so if i change that byte with a hexadecimal editor the program works just fine.

My question is: why does Turbo C commit this error? Am i doing something wrong?

Thanks

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niek_e

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Re: Tubo C strange problem

Jun 5th, 2008

•

Originally Posted by paolomontero

It's just a function that takes a string as an argument and merely loops till it finds the terminating NULL character.
[...]

Am i doing something wrong?

Yes. To find the terminating char, you did this:
while (s[n] != 0)

But 0 and the string-terminating-char aren't the same. So change it to:
while (s[n] != '\0')

Now your array will stay within it's limits.
Just a hint: You can also use strlen() which does the exact same thing, but with a lot of error checking.

Also: this thread is in the wrong forum. I'll ask if it can be moved.

I hate signature links.

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Re: Tubo C strange problem

Jun 5th, 2008

dont use trubo c. If you search this forum you would know why.

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Re: Tubo C strange problem

Jun 5th, 2008

turbo C is a piece of crap.

use the GCC compiler (free) or MSVC compiler (free) with the Code::Blocks IDE (free).

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Re: Tubo C strange problem

Jun 5th, 2008

Thanks for replying.

niek_e, you are right about the comparing but thats not the problem. It seems to me that you misunderstood my post, if you look at the disassembly, the array position is not ok when passed to the function, independent of what the function does.

I need to use Turbo C, so i think this thread should be in Legacy, i dont know why it was moved, because the discussion isnt about C but The Turbo C compiler itself.

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Re: Tubo C strange problem

Jun 5th, 2008

hi. Paolo. i wish i had an answer for you. i would try, but i don't have the compiler to replicate it with.

well, i can see now you're not the typical Turbo C user who just doesn't know any better. ... so if you don't mind, i'd like to know why do you need to use it? curious.

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paolomontero paolomontero is offline

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Re: Tubo C strange problem

Jun 5th, 2008

jephthah, thank you very much for your interest.

Im developing an operating system (if you can call it that) as a project of my own and just for personal use. Im really excited about this.

I already have my bootloader coded in nasm and it works.

Now im working on the kernel mixing Turbo C and nasm. I want to stay in 16 bit and thats why i use Turbo C, i have tried other compilers (there arent many 16 bit C compilers for windows) but they didnt work or maybe i couldnt get them to work.

The problem is not mixing Turbo C with nasm or the fact that the program will not sit on dos whatsoever. If i just wanted to write a program with a function that takes an array or a pointer as a parameter and compile-link it with the tiny memory model, i couldnt. I really have no clue of why the address is not correct.

Thanks,

Gabriel

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Re: Tubo C strange problem

Jun 6th, 2008

The program you're writing will work on ANY C compiler, even piece of crap compilers, which Turbo C is not one of. It pisses me off every time someone denegrates good compilers just because they are older. If they do exactly what the user needs, it's fine. It just can't do advanced 32bit stuff that the user obviously doesn't need. It still is C. It still works fine. And TC can still do things none of the current compilers can do.

I agree upgrading should be considered, but is not necessary. And definitely TC should not be put down.

Last edited by WaltP; Jun 6th, 2008 at 2:02 am.

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Re: Tubo C strange problem

Jun 6th, 2008

OK, i knew about that already and thats why im using Turbo C.

But im still having the problem i posted at the begging! Anyone can help me with that? If somebody wants my messenger to instruct me easier ill be happy to pm it.

Or maybe someone can recommend me another 16 bit compiler, and how to compile and link the project (i have watcom but i havent been able to get it to work).

Thanks,

Gabriel

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Re: Tubo C strange problem

#10

Jun 9th, 2008

I don't have Turbo C 2.0, but this runs fine in Turbo C/C++ ver. 1.01, as a C program. Note int main and the include header.

IIRC Turbo C 2.0 came before Turbo C/C++, but it's been a long time.

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
#include <stdio.h>  
 
void f(char *);
 
char h[] = "hello";
 
int main() {
   int gar;
   f(h);
   gar = getchar(); gar++;
   return 0; 
}
void f(char *s) {
   int n = 0;
 
   while (s[n] != '\0') {
      /*do something*/
      putchar(s[n++]);
   }
}
#include <stdio.h>  

void f(char *);

char h[] = "hello";
  
int main() {
   int gar;
   f(h);
   gar = getchar(); gar++;
   return 0; 
}
void f(char *s) {
   int n = 0;
  
   while (s[n] != '\0') {
      /*do something*/
      putchar(s[n++]);
   }
}