C从另一个文件嵌入结构的更改值

Question

Hello I am working on a small roboter project at uni and I have run into following issue. I have a typedef called RoboterData inside of a header file because I want to make use of it across multiple files. Inside of the main file I have a RoboterData data variable which holds important data.

My goal is to have access from other files to this data having the ability to get and set it from another file. I want to avoid the use of a global variable.

Here are the relevant code fragments of my approach:

main.h

typedef struct {
    DriveMode mode;
    short sensor_left;
    short sensor_mid;
    short sensor_right;
    int left_eng_speed;
    int right_eng_speed;
} RoboterData;

main.c

# include "motors.h"

// The Data I want to get and set from other files.
RoboterData data;

// Call to a funcion defined in motors.c
drive_straight(RoboterData *data);

motors.h

void drive_straight(RoboterData *data);

motors.c

# include "main.h"

enum {
    ENG_STILL = 0,
    ENG_SLOW = 50,
    ENG_MID = 155,
    ENG_FAST = 200
}

void drive_straight(RoboterData *data) {
    data ->left_eng_speed = ENG_FAST;
    data ->right_eng_speed = ENG_FAST;
    set_duty_cycle(LEFT_ENG, ENG_FAST);
    set_duty_cycle(RIGHT_ENG, ENG_FAST);
}

When I later try to print out the values left_eng_speed and right_eng_speed via serial port it stays at 0. I know C is call by value but since I am passing a ptr to my struct the value I am passing is the adress of the struct and when I dereference it via '->' I should be able to access its original data from my understanding and not a copy because the only thing I copied was the address.

If someone could explain to me why this is not working and provide a viable alternative, I would be very greatfull.

Answer 1

// Call to a funcion defined in motors.c
drive_straight(RoboterData *data);

This is a function declaration. It doesn't do anything. You want

drive_straight(&data);

to actually call the function.