c - 在 Debian Linux 上使用 gcc 或 g++ 运行 C/C++ 代码时出错

Question

我两天前开始使用 Debian Linux。 安装gcc、g++编译器后， 我想使用命令(gcc file.c)运行 C 代码，但我在终端中发现了一个奇怪的错误。

/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/crt1.o: In function `_start':
(.text+0x20): undefined reference to `main'
collect2: error: ld returned 1 exit status

操纵杆.c

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>

#include "joystick.h"

static int joystick_fd = -1;

/* These are sensible on Logitech Dual Action Rumble and xbox360 controller. */
static int joystick_x_axis = 0;
static int joystick_y_axis = 1;

int open_joystick(char *joystick_device)
{
    if (joystick_device == NULL)
        joystick_device = JOYSTICK_DEVNAME;
    joystick_fd = open(joystick_device, O_RDONLY | O_NONBLOCK); /* read write for force feedback? */
    if (joystick_fd < 0)
        return joystick_fd;

    /* maybe ioctls to interrogate features here? */

    return joystick_fd;
}

int read_joystick_event(struct js_event *jse)
{
    int bytes;

    bytes = read(joystick_fd, jse, sizeof(*jse));

    if (bytes == -1)
        return 0;

    if (bytes == sizeof(*jse))
        return 1;

    printf("Unexpected bytes from joystick:%d\n", bytes);

    return -1;
}

void close_joystick()
{
    close(joystick_fd);
}

int get_joystick_status(struct wwvi_js_event *wjse)
{
    int rc;
    struct js_event jse;
    if (joystick_fd < 0)
        return -1;

    /* memset(wjse, 0, sizeof(*wjse)); */
    while ((rc = read_joystick_event(&jse) == 1)) {
        jse.type &= ~JS_EVENT_INIT; /* ignore synthetic events */
        if (jse.type == JS_EVENT_AXIS) {
            if (jse.number == joystick_x_axis)
                wjse->stick_x = jse.value;
            if (jse.number == joystick_y_axis)
                wjse->stick_y = jse.value;
        } else if (jse.type == JS_EVENT_BUTTON) {
            if (jse.number < 11) {
                switch (jse.value) {
                case 0:
                case 1: wjse->button[jse.number] = jse.value;
                    break;
                default:
                    break;
                }
            }
        }
    }
    /* printf("%d\n", wjse->stick1_y); */
    return 0;
}

void set_joystick_y_axis(int axis)
{
    joystick_y_axis = axis;
}

void set_joystick_x_axis(int axis)
{
    joystick_x_axis = axis;
}


#if 0
/* a little test program */
int main(int argc, char *argv[])
{
    int fd, rc;
    int done = 0;

    struct js_event jse;

    fd = open_joystick();
    if (fd < 0) {
        printf("open failed.\n");
        exit(1);
    }

    while (!done) {
        rc = read_joystick_event(&jse);
        usleep(1000);
        if (rc == 1) {
            printf("Event: time %8u, value %8hd, type: %3u, axis/button: %u\n",
                jse.time, jse.value, jse.type, jse.number);
        }
    }
}

操纵杆.h

#include <stdio.h>
#ifndef __JOYSTICK_H__
#define __JOYSTICK_H__

#define JOYSTICK_DEVNAME "/dev/input/js0"

#define JS_EVENT_BUTTON         0x01    /* button pressed/released */
#define JS_EVENT_AXIS           0x02    /* joystick moved */
#define JS_EVENT_INIT           0x80    /* initial state of device */


struct js_event {
    unsigned int time;  /* event timestamp in milliseconds */
    short value;   /* value */
    unsigned char type;     /* event type */
    unsigned char number;   /* axis/button number */
};

struct wwvi_js_event {
    int button[11];
    int stick_x;
    int stick_y;
};

extern int open_joystick(char *joystick_device);
extern int read_joystick_event(struct js_event *jse);
extern void set_joystick_y_axis(int axis);
extern void set_joystick_x_axis(int axis);
extern void close_joystick();
extern int get_joystick_status(struct wwvi_js_event *wjse);

#endif

#endif

Answer 1

#if 0 的存在会排除 main 被编译。将其更改为#if 1。由于您没有相应的 #endif，因此您可以完全删除该行。