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Message |
EdWaugh
Joined: 07 Dec 2004
Posts: 127
Location: Southampton, UK
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| printf and strings inside structures |
 Posted: Thu Feb 17, 2005 7:20 am |
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Hi all,
I'm having a bit of trouble with some code that I think is to do with pointers. Its perhaps more of a general problem with my C than a specific ccs one. I'm trying to write strings constant and other wise into structs. For example:
| Code: |
struct example
{
char string[16];
};
main()
{
struct example instance;
for(i=0;i<15;i++)
{
instance.string[i] = 'c';
}
printf("%s",instance.string);
}
|
I realise all the code is not there but I hope you get the idea about what I want to do. I also want to:
| Code: |
strcopy(instance.string,"hello");
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and use them from functions they are passed too:
| Code: |
fn(struct example *instance)
{
printf("%s",instance->string)
}
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Is this possible or am I making it up? It looks very reasonable to me but doesn't seem to work. I just print blanks over whatever else I was trying to print nearby. I suspect I am pointing at the wrong thing somehow as the string is a pointer inside the structure.
Anyway, any advice would be greatly appreciated I can't seem to find a good note on this subject.
cheers
ed |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Thu Feb 17, 2005 1:48 pm |
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Here is an example program that will show you how to do it.
The output of this program is:
1 2 3 Hello
I used PCM vs. 3.218 and 3.219 to test this. I used the MPLAB 7.01
simulator and directed the RS232 output to "UART1" which then
displays it in the Output window.
| Code: | #include <16F877.h>
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock = 4000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, ERRORS)
typedef struct
{
char a;
char b;
char c;
char string[10];
}ABC;
ABC test;
void func1(ABC *abc_struct);
//--------------------------------------------
void main()
{
test.a = 1;
test.b = 2;
test.c = 3;
strcpy(test.string, "Hello");
func1(&test);
}
//==========================================
// FUNCTIONS
void func1(ABC *ptr)
{
printf("%d %d %d %s\n\r", ptr->a, ptr->b, ptr->c, ptr->string);
} |
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EdWaugh
Joined: 07 Dec 2004
Posts: 127
Location: Southampton, UK
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| cheers |
| Posted: Fri Feb 18, 2005 4:56 am |
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Hi,
I have just tried a simple example at the start of my main function like the one you suggest and that does seem fine. I don't suppose you know if there if there is anything else I should be aware of to do with this? My structs and functions are several calls deep in my program and I'm using compiler version 3.172. I'm also writing to the strings like this:
| Code: |
fn(struct example *ptr)
{
strcpy(ptr->string,"hello")
}
|
Which I'm assuming is ok too. Its a very odd problem and hard to simulate as all my data I'm working on comes in over SPI!
I'll keep trying its driving me a bit nuts now.
cheers
ed |
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Ttelmah
Guest
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| Posted: Fri Feb 18, 2005 8:19 am |
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The obvious thing that might be causing problems in the original example, is that a 16 character array, can only hold a 15 character string. Remember a 'string', has a null terminator...
Best Wishes |
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EdWaugh
Joined: 07 Dec 2004
Posts: 127
Location: Southampton, UK
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| hi |
| Posted: Fri Feb 18, 2005 9:47 am |
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yea i know about that and have tried making my strings plenty big but this doesn't help either!
cheers
ed |
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Mark
Joined: 07 Sep 2003
Posts: 2838
Location: Atlanta, GA
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| Re: hi |
| Posted: Fri Feb 18, 2005 9:55 am |
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| EdWaugh wrote: | yea i know about that and have tried making my strings plenty big but this doesn't help either!
cheers
ed |
Well this doesn't do that
| Code: | struct example
{
char string[16];
};
main()
{
struct example instance;
for(i=0;i<15;i++)
{
instance.string[i] = 'c';
}
printf("%s",instance.string);
}
|
Making them big enough isn't the only thing. If you are loading characters into an array to create a string then YOU must terminate the string with a NULL yourself. |
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EdWaugh
Joined: 07 Dec 2004
Posts: 127
Location: Southampton, UK
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| Posted: Fri Feb 18, 2005 9:58 am |
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yep, ok your right, you mean a '\0' as the final char. I think maybe I'd been looking at strcpy which adds one for you and not been putting one on myself.
cheers
ed |
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