[avr-gcc-list] Re: Passing a string variable to lcd_puts

[David Brown]

David VanHorn wrote:
>         I know what *I* am missing - the source code!  How is anyone
>         supposed to help you with your problem until you post the actual
>         compilable code snippet?  We need a compilable code sample which
>         demonstrates the problem, along with the compiler flags you used
>         and also the compiler version you used.  Getting a warning for
>         int8_t but not for "signed char" is not expected behaviour, and
>         I think many people (as well as you) would be interested to find
>         out if that is really the case, and if so, if there is some
>         strange compiler issue.  But we need the code so that other
>         people can test this.
>
>  
> Fine.. I thought I must be doing something fairly trivial wrong, this IS 
> only my second project in C...
> I expected to be told that I was using lcd_puts wrong, or declaring 
> something improperly, or some other noob mistake.
> What I'm seeing is certainly unexpected to ME.
>  
> I'm very reluctant to throw out bunches of code, when the problem is 
> likely to be some trivial thing that "everyone knows".
>  

I used to have a colleague who had a large piece of foam rubber taped to 
his wall - it was labelled "bang your head here".  Sometimes I think I 
need to get one of these myself.

The code you posted is *not* a code snippet that others can compile and 
test.  It doesn't even use lcd_puts !!

Post a *minimal* code snippet that can be compiled.  There should be an 
absolute minimum of #include lines, and never any #include's that don't 
come as part of a standard avr-gcc installation.  Putting #include 
"lcd.h" is totally, utterly useless - how are we supposed to guess 
what's in lcd.h ??  Perhaps it contains the declaration for lcd_puts() - 
the function you are needing help with?


An example code snippet is shown below.

With the flag -funsigned-char and appropriate warnings enabled, this 
gives - as expected - a warning "pointer targets in passing argument 1 
of 'lcd_puts' differ in signedness" for lcd_test2, 3, and 4.  Using 
uint8_t gives no warning, because it is the same as "signed char".

I conclude from this that there is nothing wrong with the compiler or 
its error checking here - the warnings are exactly as expected. 
However, there might be something else wrong with your code - no one 
will ever know until you post the *relevant* code.


mvh.,

David



#include <stdint.h>

extern void lcd_puts(signed char *p);

extern void lcd_test1(void);    // To avoid "missing-prototype" errors
void lcd_test1(void) {
        signed char a[] = "a";
        lcd_puts(a);
}

extern void lcd_test2(void);
void lcd_test2(void) {
        unsigned char a[] = "a";
        lcd_puts(a);
}

extern void lcd_test3(void);
void lcd_test3(void) {
        char a[] = "a";
        lcd_puts(a);
}

extern void lcd_test4(void);
void lcd_test4(void) {
        uint8_t a[] = "a";
        lcd_puts(a);
}

extern void lcd_test5(void);
void lcd_test5(void) {
        int8_t a[] = "a";
        lcd_puts(a);
}