Can't call struct on another file or call the function in main code

Question

Hi, 
 I am planning to create an ultrasonic library (based on ch201) because I can't find any library for it. So I am porting code from ch201 development kit to nrf52 custom board. 
 So in my main code, I am defining a method for creating initialization just like the development kit does. Below is the header of my main code, as you can see there is 
 #include <stdio.h>
#include "boards.h"
#include "app_util_platform.h"
#include "app_error.h"
#include "nrf_delay.h"
#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"
#include "ch201.h"
#include "ch201_gprmt.h"
#include "EventRecorder.h"

#define LED_PIN 7
#define CH201_SENSOR_FW_INIT_FUNC ch201_gprmt_init

///////////// methods & variables declaration ////////////////////////
uint8_t chirp_error = 0;
uint8_t init_sensor(ch201_device *dev_ptr, ch_fw_init_func_t fw_init_func);
uint8_t start_sensor(ch201_device *dev_ptr); 
 
 In my main loop, you can check at the part of sensor initialization, there is a method called ch201_init and has 2 arguments. 
 int main(void)
{
	EventRecorderInitialize(EventRecordAll, 1);
	printf("init fw
");
	nrf_gpio_cfg_output(LED_PIN);
	nrf_gpio_pin_clear(LED_PIN);
	nrf_delay_ms(500);
 
 // I2C initiate
	printf("
Init i2c");
	twi_init();
	nrf_delay_ms(500);
	
	printf("
Write i2c");
	// find sensors
	find_sensors();
	
	// initialize sensors
	/*
	init sensor firmware
	*/
	chirp_error |= ch201_init(&sensor, CH201_SENSOR_FW_INIT_FUNC);
	if (chirp_error != 0) {
 printf("Fail initialize sensor.
");
 printf("Error: %d
", chirp_error);
	} 
 First argument for selecting sensor struct, and second argument is firmware method for initialization process. 
 
 Here is the source code for that method. 
 uint8_t ch201_gprmt_init(ch201_device *dev_ptr, uint8_t i2c_addr, uint8_t io_index, uint8_t i2c_bus_index) {
	
	dev_ptr->part_number = CH201_PART_NUMBER;
	dev_ptr->app_i2c_address = i2c_addr;
	dev_ptr->io_index = io_index;
	dev_ptr->i2c_bus_index = i2c_bus_index;

	/* Init firmware-specific function pointers */
	dev_ptr->firmware = ch201_gprmt_fw;
	dev_ptr->fw_version_string = ch201_gprmt_version;
	dev_ptr->ram_init = (uint8_t *) get_ram_ch201_gprmt_init_ptr();
	dev_ptr->get_fw_ram_init_size = get_ch201_gprmt_fw_ram_init_size;
	dev_ptr->get_fw_ram_init_addr = get_ch201_gprmt_fw_ram_init_addr;

	dev_ptr->prepare_pulse_timer = ch_common_prepare_pulse_timer;
	dev_ptr->store_pt_result = ch_common_store_pt_result;
	dev_ptr->store_op_freq = ch_common_store_op_freq;
	dev_ptr->store_scalefactor = ch_common_store_scale_factor;
	dev_ptr->get_locked_state = ch_common_get_locked_state;
	
	dev_ptr->api_funcs.fw_load = ch_common_fw_load;
	dev_ptr->api_funcs.set_mode = ch_common_set_mode;
	dev_ptr->api_funcs.set_sample_interval = ch_common_set_sample_interval;
	dev_ptr->api_funcs.set_num_samples = ch_common_set_num_samples;
	dev_ptr->api_funcs.set_max_range = ch_common_set_max_range;
	dev_ptr->api_funcs.set_static_range = NULL; // not supported
	dev_ptr->api_funcs.get_range = ch_common_get_range;
	dev_ptr->api_funcs.get_amplitude = ch_common_get_amplitude;
	dev_ptr->api_funcs.get_iq_data = ch_common_get_iq_data;
	dev_ptr->api_funcs.samples_to_mm = ch_common_samples_to_mm;
	dev_ptr->api_funcs.set_thresholds = ch_common_set_thresholds;
	dev_ptr->api_funcs.get_thresholds = ch_common_get_thresholds;

	/* Init max sample count */
	dev_ptr->max_samples = CH201_GPRMT_MAX_SAMPLES;

	/* This firmware does not use oversampling */
	dev_ptr->oversample = 0;

	/* Init device and group descriptor linkage */
	// dev_ptr->group = grp_ptr; // set parent group pointer
	// grp_ptr->device[io_index] = dev_ptr; // add to parent group

	return 0;
} 
 
 When I compile the code, it gives me error like that method is not defined yet before. But you can check at my header, I call that method from it's file (but the code is not defined at header, but I just make the code works on it is source file). 
 Below is the code when I compile it without defining it on header file. 
 ..\..\..\main.c(95): error: #20: identifier "ch201_gprmt_init" is undefined
 chirp_error |= ch201_init(&sensor, &CH201_SENSOR_FW_INIT_FUNC); 
 ******** 
 So I was planning to define it on header library. But, when I define it on header library, it gives me more errors message than before. 
 So as you can check in the picture below, now I define it and looks like no errors on it.

But, when I compile, it gives me more errors (4 errors). It is said the ch201_device is not defined, but I define it at my main library code. Below is the error result. 
 ..\..\..\..\..\..\components\libraries\ch201\ch201_gprmt.h(38): error: #20: identifier "ch201_device" is undefined
 uint8_t ch201_gprmt_init(ch201_device *dev_ptr, uint8_t i2c_addr, uint8_t dev_num, uint8_t i2c_bus_index); 
 
 So Is there any solution for this? Thank you for your appreciation.

ovrebekk · Accepted Answer

Hi Imam 
 Is ch201_device defined in a different header file than ch201_gprmt.h? 
 If so you need to include that header file at the top of ch201_gprmt.h, so that the ch201_device struct is defined at the point where you declare the ch201_gprmt_init function. 
 For all of this to work make sure you are using include guards , to ensure that you don't define things multiple times (this would cause even more errors). 
 Best regards Torbjørn

Can't call struct on another file or call the function in main code

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