ラズパイのGPIOにアクセスする既存のライブラリが使えなかったので自分で作った。

rplib.c

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

#define INPUT 0
#define OUTPUT 1

typedef struct
{
    int id;
} GPIO;

int gpio_open(int id, char* mode)
{
    FILE *fp;
    char filename[128];

    fp = fopen("/sys/class/gpio/export", "w");
    if(fp == NULL)
        return -1;
    fprintf(fp, "%d", id);
    fclose(fp);

    sprintf(filename, "/sys/class/gpio/gpio%d/direction", id);
    fp = fopen(filename, "w");
    if(fp == NULL)
        return -1;
    fprintf(fp, "%s", mode);
    fclose(fp);

    return 0;
}

GPIO gpio_open_reader(int id)
{
    GPIO gpio = { -1 };
    if(gpio_open(id, "in") == -1)
        return gpio;
    gpio.id = id;
    return gpio;
}

int gpio_read(GPIO gpio)
{
    int fd;
    char filename[128];
    char c;

    sprintf(filename, "/sys/class/gpio/gpio%d/value", gpio.id);
    fd = open(filename, O_RDONLY);
    read(fd, &c, 1);
    close(fd);

    return c == '1' ? 1 : 0;
}

GPIO gpio_open_writer(int id)
{
    GPIO gpio = { -1 };
    if(gpio_open(id, "out") == -1)
        return gpio;
    gpio.id = id;
    return gpio;
}

int gpio_write(GPIO gpio, int data)
{
    int fd;
    char filename[128];
    char c[2] = {'0', '1'};

    sprintf(filename, "/sys/class/gpio/gpio%d/value", gpio.id);
    fd = open(filename, O_WRONLY);
    write(fd, c + (data ? 1 : 0), 1);
    close(fd);

    return 0;
}

int gpio_close(GPIO gpio)
{
    FILE *fp;

    fp = fopen("/sys/class/gpio/unexport", "w");
    if(fp == NULL)
        return -1;
    fprintf(fp, "%d", gpio.id);
    fclose(fp);
    return 0;
}