I think if you look at the preprocessed version of memory.c
(gcc -E memory.c
) that the declaration of LCD_dataline_R
from lcd.h
is missing. Most likely this is caused by some #if
, #ifdef
or #ifndef
in lcd.h
.
Accessing external function using function pointer in C
-
21-04-2022 - |
質問
Im trying to link to a extern function using a pointer to it. But everytime I try, I get compiler errors that the extern function is undeclared. I have little experience with external functions, and so cannot see my mistake. I have a function declared in lcd.c, which I am trying to get to from a seperate file memory.c.
I need to use function pointers as I am writing an emulator, and I have a array of memory address where each element of the array links to the hardware function called if that memory address is accessed. Basically allowing me to do:
UINT8 WriteMem(int address, UINT8 data) {
return memory[address](data);
}
Heres my code im having problems with:
lcd.c
UINT8 LCD_dataline_R(UINT8 data) {
// Some code
return aValue;
}
lcd.h
extern UINT8 LCD_dataline_R(UINT8 data);
memory.c
#include "lcd.h"
typedef UINT8 (*MemFunct)(UINT8 data);
MemFunct ReadDataLine = LCD_dataline_R;
.
.
UINT8 recieved = ReadDataLine(0x80);
I'm compiling the code using GCC on Linux Mint
and get the error
Running command: make -f makefile memory.o
gcc -c -Wall memory.c
memory.c:3:25: error: ‘LCD_dataline_R’ undeclared here (not in a function)
Edit
Heres the makefile:
CC=gcc
CFLAGS=-Wall -std=c99 `sdl-config --cflags` `pkg-config --cflags gtk+-2.0`
LIBS=`sdl-config --libs` `pkg-config --libs gtk+-2.0`
all: psiora clean
memory.o: memory.c psiora.c lcd.c
$(CC) -c $(CFLAGS) $^
clean:
rm -rf *o psiora
Im only trying to compile memory.o at the moment so I've cut it down to just that part
解決
他のヒント
I don't know what is wrong with your program, but here is an example of a situation that may reproduce a similar error.
foo.h:
extern void foo(int a);
foo.c:
#include "foo.h"
void foo(int a)
{
}
bar.c:
//#include "foo.h" --> Uncomment to remove error
typedef void(*fptr)(int a);
fptr fooptr=foo;
On compiling,
gcc -c foo.c bar.c
i get a similar error:
bar.c:3: error: 'foo' undeclared here (not in a function)