Template:LIBGPIOD V2 C EXAMPLE

libgpiod C Application

[ libgpiod] provides bindings for C/C++ applications. C++ examples are available in the libgpiod [/tree/bindings/cxx/examples /tree/bindings/cxx/examples ] directory.

Below is a simple C application demonstrating how to use the bindings with GPIO4_IO21:

Makefile:

LDFLAGS = -lgpiod

TARGET = main
SRCS = main.c

all: $(TARGET)

$(TARGET): $(SRCS)
	$(CXX) $(SRCS) $(LDFLAGS) -o $(TARGET)

clean:
	rm -f $(TARGET)

main.c

// SPDX-License-Identifier: GPL-2.0-or-later
// SPDX-FileCopyrightText: 2023 Kent Gibson <warthog618@gmail.com>

/* Minimal example of reading a single line. */

#include <errno.h>
#include <gpiod.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/* Request a line as input. */
static struct gpiod_line_request *request_input_line(const char *chip_path,
						     unsigned int offset,
						     const char *consumer)
{
	struct gpiod_request_config *req_cfg = NULL;
	struct gpiod_line_request *request = NULL;
	struct gpiod_line_settings *settings;
	struct gpiod_line_config *line_cfg;
	struct gpiod_chip *chip;
	int ret;

	chip = gpiod_chip_open(chip_path);
	if (!chip)
		return NULL;

	settings = gpiod_line_settings_new();
	if (!settings)
		goto close_chip;

	gpiod_line_settings_set_direction(settings, GPIOD_LINE_DIRECTION_INPUT);

	line_cfg = gpiod_line_config_new();
	if (!line_cfg)
		goto free_settings;

	ret = gpiod_line_config_add_line_settings(line_cfg, &offset, 1,
						  settings);
	if (ret)
		goto free_line_config;

	if (consumer) {
		req_cfg = gpiod_request_config_new();
		if (!req_cfg)
			goto free_line_config;

		gpiod_request_config_set_consumer(req_cfg, consumer);
	}

	request = gpiod_chip_request_lines(chip, req_cfg, line_cfg);

	gpiod_request_config_free(req_cfg);

free_line_config:
	gpiod_line_config_free(line_cfg);

free_settings:
	gpiod_line_settings_free(settings);

close_chip:
	gpiod_chip_close(chip);

	return request;
}

static int print_value(unsigned int offset, enum gpiod_line_value value)
{
	if (value == GPIOD_LINE_VALUE_ACTIVE)
		printf("%d=Active\n", offset);
	else if (value == GPIOD_LINE_VALUE_INACTIVE) {
		printf("%d=Inactive\n", offset);
	} else {
		fprintf(stderr, "error reading value: %s\n",
			strerror(errno));
		return EXIT_FAILURE;
	}

	return EXIT_SUCCESS;
}

int main(void)
{
	/* Example configuration - customize to suit your situation. */
	static const char *const chip_path = "/dev/gpiochip3";
	static const unsigned int line_offset = 21;

	struct gpiod_line_request *request;
	enum gpiod_line_value value;
	int ret;

	request = request_input_line(chip_path, line_offset, "get-line-value");
	if (!request) {
		fprintf(stderr, "failed to request line: %s\n",
			strerror(errno));
		return EXIT_FAILURE;
	}

	value = gpiod_line_request_get_value(request, line_offset);
	ret = print_value(line_offset, value);

	/* not strictly required here, but if the app wasn't exiting... */
	gpiod_line_request_release(request);

	return ret;
}