Alan,
You don't need a global pointer. The name of an array is the address of
the first element, so array[0] is the same element as *array. It's a
little confusing sometimes, but extremely useful, and not just with basic
elements like characters.
For instance if you want to declare memory space for a structure and also
use its name as a pointer, you can do this: struct some_type some_name[1];
You can now pass some_name as a pointer, or assign it to another pointer.
Sincerely,
David Smead
www.amplepower.com
www.amplepower.net
On Mon, 20 Aug 2007, Alan007 wrote:
Dear All,
Thank you for your posts. I have tried to pass the address of the first
element of my string to put_message, but that didn't work either. I have got
around my problem, by declaring a global pointer and then inside my function
that has to call put_message, I initialise my global pointer to the address
of the begining of the string.
By doing the above, my program does what I expect.
The original put_message function that I use in my code outputs characters
to a serial port. I didn't post this code onto the newsgroup. I stripped
this function down, to do something basic (incrementing the 1st value of an
array) as you will see in my earlier post and this causes the same problem
to occur, which is why I posted the stripped down code rather that the
output to serial port code.
I'm just using the default compiler flags to compile my code. If they were
changed to something else, would my program be likely to perform
differently?
Thanks again for any help,
Regards,
Alan
bweiss wrote:
Hi Alan,
Not quite sure what the function is supposed to actually do given your
code fragment there.
GCC works quite well with unsigned char pointers, though gdb might be
slightly harder to use with them from the command line.
I can't say I've ever really had to debug string stuff thus far.
My string print function is simply
void uart_txs( uint8_t* s)
{
while(*s != '\0')
uart_tx(*s++);
}
Haven't had any problems with it at all.
I regularly call it as uart_txs("Hello\r\n");
If you actually have in your put_message function the whole
msg[0]++;
thing then it might cause issues. String literals are constants and
shouldn't be modified unless you really know what you're doing, and where
the string literal has been placed.
Regards,
Bevan
Date: Thu, 16 Aug 2007 03:03:08 -0700
From: [email protected]
To: [email protected]
Subject: [Mspgcc-users] passing a pointer to a function with MSP430 gcc
Dear All,
I'm trying to recompile some c code that was initially with IAR in gcc.
My
function that doesn't work, is supposed to write characters to a serial
port.
The prototype of my function to write to a serial port, is:
void put_message( unsigned char *s);
I then call this function like so:
put_message( "TEST");
If I put a breakpoint inside the put_message function and examine the
value
of *s, I get 0. I've examined the "memory map" around s in gcc, and the
memory locations after s are also set to 0.
Does gcc not like unsigned char pointers?
Here's a small snippet of code where the problem occurs:
#include <msp430x42x.h>
void put_message(unsigned char *msg){
msg[0]++;
msg[0]++;
msg[0]++;
msg[0]++;
}
int main(void){
int i = 0;
unsigned char message[10];
message[0]=1;
message[1]=2;
message[2]=3;
message[3]=4;
P1SEL = 0;
P1DIR = P1DIR | 0x8;
while (1){
P1OUT = P1OUT | 0x8;
for (i=0;i<1000;i++){}
P1OUT = P1OUT & 0xf7;
for (i=0;i<1000;i++){}
put_message(message); //neither of these function calls produce
the
correct value in put_message
put_message("test");
}
}
Do you have any suggestions? Thanks in advance for your help,
Regards,
Alan
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