Assume that you are using C and C has a facility to bind together object
modules from different files.
You define a function in one file, it has a bunch of parameters and doesn’t
return anything.
In another file you use that function but don’t have a prototype that tells the
compiler anything about the function.
Now assume that the compiler was written in 1972, and doesn’t benefit from
things like mind reading.
C assumes, by default, that a function has one integer parameter and returns an
integer, unless otherwise told. What other choices has it got? Nothing really.
So in later versions of C, they introduced a thing called a prototype that
gives the compiler a hint about the parameters and return values of a function.
All that you needed was to take your function header, put a semicolon on the
end and paste it before the call to the function and the compiler would have
done what you wanted instead of what you said.
Better yet, take that prototype and put it into a header file and whenever you
want to call the function, put in an include statement, the compiler get’s the
information about the parameters and return values, and overrides the int func(
int) default nature.
A
> On 2019-June-26, at 12:41 AM, Jython <googch...@gmail.com> wrote:
>
> I have a function named oled_write_temp in a.c, if i dont declare it in a.h
> , then i will get the wrong supply value in the function within main call,
> why?
>
> if i declare it in a.h, then all is right
>
> void oled_write_temp(float set_temp, const float supply, float return_temp)
> {
>
> int base_x = 12, base_y = 60;
>
> char buffer[20] = {0};
>
> printf("supply_temp %f at %s\n", supply, __FUNCTION__);
>
> snprintf(buffer, 20, "SUPPLY:%.2f", supply);
> printf("supply_temp string %s\n", buffer);
>
> oled_clear_area(base_x, base_y + 16, 122, base_y + 32);
> OLED_ShowString(base_x, base_y + 16, buffer, 16, 1);
>
> memset(buffer, 0, sizeof(buffer));
> snprintf(buffer, 20, "RETURN:%.2f", return_temp);
> OLED_ShowString(base_x, base_y + 36, buffer, 16, 1);
>
> memset(buffer, 0, sizeof(buffer));
> snprintf(buffer, 20, "SET :%.2f", set_temp);
> OLED_ShowString(base_x, base_y + 56, buffer, 16, 1);
>
> }
>
> ps: watch line printf("supply_temp %f at %s\n", supply, __FUNCTION__);
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