How do I pass an array of structures to a function?

user_16074275 0
Viewed 125

I'm trying to pass an array of structs to a function which fills them with data.

When I try to compile the code I am told that there is an error:

In function 'main':
    error: expected expression before 'Robot_t'
        loading_Profiles (Robot_t RobotInfo[]);

I am not sure what I am missing?

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <math.h>
#include <string.h>

typedef struct {
    int Robot_Number;
    char Robot_Name[30];
    int Year_Manufacturer;
    float Top_Speed;
    float Mass;
    float Best_Score;
} Robot_t;

void loading_Profiles();

int main()
{
    Robot_t RobotInfo[5];

    loading_Profiles (Robot_t RobotInfo[]);

    int i;
    for (i = 0; i < 50; i++) {
        printf("%d\t\t%s\t\t%d\t\t\t%.2f\t\t%.2f\t\t%.2f\n",
               RobotInfo[i].Robot_Number, RobotInfo[i].Robot_Name,
               RobotInfo[i].Year_Manufacturer, RobotInfo[i].Top_Speed, 
               RobotInfo[i].Mass, RobotInfo[i].Best_Score);
    }
    return 0;
}

void loading_Profiles()
{
    int Counter = 0;
    int i;

    Robot_t RobotInfo[5];

    FILE *ROBOTtxt = fopen("Robot.txt", "r");

    if (ROBOTtxt == NULL) {
        perror("an error occured during the loading of the file\n");
        exit(-1);
    }

    for (i = 0; i < 50; i++) {
        char LineNumber[100] = "";
        fgets(LineNumber, 100, ROBOTtxt);
        sscanf(LineNumber, "%d %s %d %f %f %f",
               &RobotInfo[i].Robot_Number,
               RobotInfo[i].Robot_Name,
               &RobotInfo[i].Year_Manufacturer,
               &RobotInfo[i].Top_Speed,
               &RobotInfo[i].Mass,
               &RobotInfo[i].Best_Score);

        Counter++;

        if (feof(ROBOTtxt)) {
            break;
        }
    }

    if (ferror(ROBOTtxt)) {
        perror("an error has occured");
        exit(-1);
    }

    fclose(ROBOTtxt);
}
c
3 Answers

There are several issues with your program. The obvious one is that your function prototypes do not match:

void loading_Profiles()

should be

void loading_Profiles(Robot_t *robots)

in both the declaration and definition.

The array Robot_t RobotInfo[5] in main, and the Robot_t RobotInfo[5] in loading_Profiles do not refer to the same array. They are separate arrays, local to each function. You need to pass the array from main to the loading_Profiles function, which should then modify the array.

Your code also contains various size errors. You are defining an array of 5 elements, and then trying to read and write up to 50 elements. Beyond the mismatch, you need to think about what happens if your file contains less lines than expected.

Counter is unused. As are the return values of some functions that can indicate status / errors:

  • fgets already partially indicates if it has reached EOF by returning NULL.

  • sscanf returns the numbers of conversions that took place, which can be used to make sure a partial set of data wasn't stored.

Here is a rewritten example that showcases how to pass arrays around, fill them to a maximum, and utilize the return values of stdio functions. Notice how the type signature of load_robot_profiles matches exactly between the declaration, definition, and invocation of the function.

#include <stdio.h>
#include <stdlib.h>

typedef struct {
    int number;
    char name[32];
    int year_manufactured;
    float top_speed;
    float mass;
    float best_score;
} Robot;

size_t load_robot_profiles(Robot *, size_t, const char *);

int main(void) {
    Robot robots[5];
    size_t length = load_robot_profiles(robots, 5, "robots.txt");

    for (size_t i = 0; i < length; i++) {
        Robot *r = &robots[i];

        printf("%d\t%s\t%d\t\t%.2f\t%.2f\t%.2f\n",
                r->number, r->name, r->year_manufactured,
                r->top_speed, r->mass, r->best_score);
    }
}

size_t load_robot_profiles(Robot *robots, size_t size, const char *fname) {
    size_t i = 0;
    FILE *file = fopen(fname, "r");
    char input[128];

    if (!file)
        return 0;

    while (i < size && fgets(input, sizeof input, file)) {
        Robot *r = &robots[i];

        if (6 == sscanf(input, "%d %s %d %f %f %f",
                &r->number, r->name, &r->year_manufactured,
                &r->top_speed, &r->mass, &r->best_score))
            i++;
    }

    fclose(file);

    return i;
}

Also note: Defining a type with a _t suffix is ill-advised, as eventually you will brush up against a conflict with an existing POSIX type, or other standard.

user_25059650

Your definition and declaration of the function void loading_Profiles() don't include any arguments, but you're calling it with an argument: loading_Profiles (Robot_t RobotInfo[]);.

You need to change the function to accept Robot_t RobotInfo[] as an argument and then modify the RobotInfo[] array.

user_110394900

The function signature should be like that:

void loading_Profiles(Robot_t* RobotInfo);

Also, there is no need to redeclare the Robot_t RobotInfo[5] inside your loading_Profiles function, since it is already passed by the function call.

user_120617460
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