无法使用宏包装cgo标志

Question

I made a Go program to simulate key presses. To do that I had to use cgo and different snippet of C code depending on the OS the Go code was being compiled. The code that I wrote looks like this:

package keyboard

/*
#include <stdint.h>
#ifdef __WIN32
#cgo CFLAGS:-nostdlib
#include <Windows.h>

void SetKey(uint16_t key, uint8_t value) {
    INPUT ip;

    ip.type = INPUT_KEYBOARD;
    ip.ki.wScan = 0;
    ip.ki.time = 0;
    ip.ki.dwExtraInfo = 0;

    ip.ki.wVk = key;
    if (value) {
        ip.ki.dwFlags = 0;
    } else {
        ip.ki.dwFlags = KEYEVENTF_KEYUP;
    }

    SendInput(1, &ip, sizeof(INPUT));
}
#endif

#ifdef __linux__
#cgo LDFLAGS: -lX11 -lXtst
#include <stdlib.h>
#include <stdio.h> //TODO: REMOVE

#include <X11/Xlib.h>
#include <X11/keysym.h>
#include <X11/extensions/XTest.h>

void SetKey(uint16_t key, uint8_t value) {
    Display *display;
    display = XOpenDisplay(NULL);

    if(display == NULL) {
        exit(EXIT_FAILURE);
    }

    XTestFakeKeyEvent(display,XKeysymToKeycode(display,key), value, 0);
    XCloseDisplay(display);
}
#endif
*/
import "C"

func SetKey(keyId uint16, value bool) {
    C.SetKey(C.uint16_t(keyId),boolToByte(value));
}

func boolToByte(value bool) C.uint8_t {
    if(value) {
        return 1
    } else {
        return 0
    }
}

The code compiles fine on Ubuntu, but on Windows 10 I get the following error

C:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/5.1.0/../../../../x86_64-w64-mingw32/bin/ld.exe: cannot find -lX11
C:/TDM-GCC-64/bin/../lib/gcc/x86_64-w64-mingw32/5.1.0/../../../../x86_64-w64-mingw32/bin/ld.exe: cannot find -lXtst

even if the line #cgo LDFLAGS: -lX11 -lXtst is wrapped around #ifdef __linux__ and #endif. Where does the problem lie on? Does the GCC compiler define the __linux__ macro? Is the keyword #cgo not supposed to be used like that?

Answer 1

The #cgo directives are used by the go tools, not the C pre-processor.

In the cgo documentation, there are examples of using build constraints to conditionally set the flag values. What you want is

#cgo windows CFLAGS:-nostdlib
#cgo linux LDFLAGS: -lX11 -lXtst