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for some reason when i use a pointer to a char to specify a string to print the copmuter reboots..any ideas?

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
main kernel

#include "text.h"

asm("jmp _main");


int main()
{
char *temp="hello";
print(temp);
return 0;
};
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
print function..................
CURLINE, CURPOS = start of text output


void print(char *string) //uses curline, curpos
{
char *vidmem;
vidmem=(char *) 0xb8000;

while(*string!=0)
{
if(CURLINE==(MAXLINE+1))
{
scrolldown();
CURLINE--;
};

if(CURPOS<80)
{
vidmem[((CURLINE*160)+(CURPOS*2))]=*string;
vidmem[((CURLINE*160)+(CURPOS*2) + 1)]=BACKROUND;
*string++;
CURPOS++;
};

if(CURPOS==80)
{
CURPOS=0;

if(CURLINE==MAXLINE)
{
scrolldown();
CURLINE--;
};

CURLINE++;
};
};
};

The sole thing that I can see is on this line:


And that's just because I didn't do it that way, but I think it should be string++ (no asterisk). I can't imagine this would cause the computer to reboot, especially if the line got through your compiler. Hey, stranger things have happened. Sorry I can't be of more help.

*string++;

that could possibly reboot the machine by causing a trap if the memory location the string is at isn't there, or incrementing goes over a boundary.

As for the printing problem, i am somewhat lost of what these lines are attempting to do:

vidmem[((CURLINE*160)+(CURPOS*2))]=*string;
vidmem[((CURLINE*160)+(CURPOS*2) + 1)] = BACKROUND;

so that is saying, make that vidmem[...] = *string? I am not too sure but I don't believe you want to make all of that simply equal "hello". I believe that you might have those backwards.

I hope this helps figure that out.
-GT

I think *string++; does not cause any problem because what compiler ++ operator has more precedence than * operator so, this expression will increase address string is pointing to and then return the value at the PREVIOUS address that it is pointing to. As far as I know about c I could not see a problem about the code, however if you have enabled paging this might cause a page fault but this is very unlikely I mean your string should be crossing a page boundary, I advice you to comment out all the lines that you think are working and then try to find which line is not working... Hope this helps... Good luck.

FOR GT....

vidmem[((CURLINE*160)+(CURPOS*2))]=*string;
vidmem[((CURLINE*160)+(CURPOS*2) + 1)] = BACKROUND;

80x25 = screen

CURLINE*2 will calc the offset beginning at the current line number. CURPOS *2 will calc the offset and add it to the curline

ex.

say i wanted to print text on line 2 but start printing text 5 spaces from the left.

CURLINE = 2
CURPOS = 5

since each line has 160 bytes....CURLINE*160 will give the offset of the line.

CURPOS will be added to curline to get an offset. it is multiplied by two because i dont count the attribute byte as a position. its easier to print text this way. i think

it might also help to know that it works with ...

print("slacker's os");

but not with variables..
print(variable);

ok people. im a dumbshit.

i needed to have my ASM code first.....
thanks for your help..it works now..


asm("jmp _start");

#include "text.h"

void start()
{
char *temp="hello joe, my name is bill";
clear();
CURLINE=3;
CURPOS=0;

print("hello my name is joe");
print(temp);
asm("hlt");

};