I am missing a fundamental point on passing values.
In my code, I wrote this prototype/function:
void drawFont (char A[],unsigned char length, char x1, char y1, uint16 FGcolor);
I call the function using a call like this:
drawFont ("William",7,15,25,YEL,0);
or
drawFont ("W",1,15,25,YEL,0);
Both of these work fine in the code. If I examine A[0] in the function, I will see a value of '57' representing an ASCII 'W'. All fine and good.
My question/problem is: When I attempt to replicate the 'W' using the ASCII value instead of the string representation, my code fails Example:
drawFont (57,1,15,25,YEL,0);
The value of A[0] in the code is: 0, but the address of A is 57. So somehow the compiler assumes that I want to pass a pointer? I'm confused, why did it pass the string fine, but not the value?
Thanks in advance from a novice C programmer.
The prototype for your function declares that the first parameter is a pointer to a character:
void drawFont (char A[],...);
If you pass an integer, you are breaking the rules. The compiler should warn about it. Mine gives a warning about the following code on the line with func(57):
void func(char a[])
{
}
char arr[] = {87,84,70};
int main()
{
func(57);
func("W");
func(arr);
}
x.c(9) : warning C4047: 'function' : 'char *' differs in levels of indirection from 'int'
x.c(9) : warning C4024: 'func' : different types for formal and actual parameter 1
If you look at the assembly output from the compiler, you can see the problem more clearly (I cut out the uninteresting parts):
PUBLIC _arr
_DATA SEGMENT
_arr DB 057H ;Here's the char array at an address in memory.
DB 054H
DB 046H
ORG $+1
$SG1297 DB 'W', 00H ;Here's the "W" at an address in memory (nul-terminated)
_DATA ENDS
; 9 : func(57);
00003 6a 39 push 57 ; Push 57 as the address, WRONG!
00005 e8 00 00 00 00 call _func
0000a 83 c4 04 add esp, 4
; 10 : func("W");
0000d 68 00 00 00 00 push OFFSET $SG1297 ; Push the address of the string.
00012 e8 00 00 00 00 call _func
00017 83 c4 04 add esp, 4
; 11 : func(arr);
0001a 68 00 00 00 00 push OFFSET _arr ; Push the address of the array.
0001f e8 00 00 00 00 call _func
00024 83 c4 04 add esp, 4
The code is expecting to go to an address to read characters. Who knows what is in address 57.
Collected from the Internet
Please contact [email protected] to delete if infringement.
Comments