STM CircleOS forum / Using "built-in" functions like strlen()

dalewheat · 2007-11-03 10:34:03

I prefer centered text on the LCD for legibility, so I wrote a small function to center text for me after I got tired of calculating the offsets in my head:

Code:

void DRAW_DisplayStringCenter ( u8 y, char *s ) {

   u8 x;

   x = ( SCREEN_WIDTH - ( strlen ( s ) * DRAW_GetCharMagniCoeff () * CHAR_WIDTH )) / 2;
   DRAW_DisplayString ( x, y, s, strlen ( s ) );
}

This code works well enough and takes the current 'character magnification coefficient' into consideration as well. It's not complicated.

I used the strlen() function twice here: once in calculating the horizontal offset and again to inform the DRAW_DisplayString() function how many characters to display. A more optimized solution would determine the string length once and store it in a local variable instead of calling the strlen() function twice with the same, unchanged parameter.

As written, this code will build but generates a warning:

Code:

warning: incompatible implicit declaration of built-in function 'strlen'

If I #include the string function header file...:

Code:

#include <string.h>

then the above warning goes away but it replaced with another one:

Code:

warning: passing argument 1 of 'strcmp' make pointer from integer without a case

...complaining of the use of the strcmp() function in the CircleOS version check at the beginning of the application initialization function, Application_Ini(), because the UTIL_GetVersion() function, which is documented as returning a "const char *" is actually returning a "u32" per the circle_api.h include file.

Adding a cast to the function call removes the warning. I'm not sure how to correct the header file as I am unfamiliar with the technique being used in the function declarations.

Thanks,

Dale Wheat

Francis · 2007-11-03 22:09:08

It's a mistake in the circle_API.h header file. UTIL_GetVersion() should return a "const char"".

# 1 2007-11-03 10:34:03 Using "built-in" functions like strlen()

Using "built-in" functions like strlen()

Code:

Code:

Code:

Code:

# 2 2007-11-03 22:09:08 Using "built-in" functions like strlen()

Re: Using "built-in" functions like strlen()

Board footer