使用指针传递结构体数组并返回结构体数组-函数

Question

I realize this question has been asked often but I still dont really understand how it works. I want to try and read my file into my structures, inside a function and pass the structures through pointers to the function. I am unsure about how to even write the function prototype.

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

#define MAX 90
#define STR 200
#define MAXLEN 40

struct human {
    char name[MAXLEN];
    char surname[MAXLEN];
    int age;
    float weight;
};
int main(int argc, char *argv[]) {
    char *dlim= " ", *end = "\n";
    char *string;
    string = (char *)malloc(sizeof(char) * STR);
    int i = 0, j = 0;
    struct human *man = malloc(sizeof(struct human) * MAX);

    FILE *fin = fopen("data.txt", "r");
    if (fin == NULL) {
        printf("Cannot open file\n");
        exit(0);
    }
    while (fgets (string, STR, fin)){
        read (string, &man[i], dlim, end);
        i++;
    }
    fclose(fin);

    free(string);
    free(man);

  return 0;
}

struct human *man read(char *fstring, struct *man, char *div, char *end){
   int i=0;
   char *tok;

        tok = strtok(string, dlim);
        strcpy(man[i].name, tok);

        tok = strtok(NULL, dlim);
        strcpy(man[i].surname,tok);

        tok = strtok(NULL, dlim);
        man[i].age = atoi(tok);

        tok = strtok(NULL, end);
        man[i].weight = atof(tok);

   return man[i];

}

Whats the function meant to look like? And am i correct in assuming that through the use of pointers, the struct will be automatically be updated in main, without needing to return something in the function?

Can the function also return nothing (void), because the use of pointers will automatically pass onto main?

Thank you!

Answer 1

Your code is close but the pointer logic in the subroutine that fills in the human structure is incorrect. See if the following rework, and slight simplification, helps you understand how to pass the structure:

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

#define MAXIMUM_HUMANS 90
#define MAXIMUM_INPUT_STRING_LENGTH 200
#define MAXIMUM_STRING_LENGTH 40

struct human {
    char name[MAXIMUM_STRING_LENGTH];
    char surname[MAXIMUM_STRING_LENGTH];
    int age;
    float weight;
};

void initialize_human(char *string, struct human *man, char *delimiter, char *end) {
    char *token;

    token = strtok(string, delimiter);
    strcpy(man->name, token);

    token = strtok(NULL, delimiter);
    strcpy(man->surname, token);

    token = strtok(NULL, delimiter);
    man->age = atoi(token);

    token = strtok(NULL, end);
    man->weight = atof(token);
}

int main(int argc, char *argv[]) {
    char *dlim= " ", *end = "\n";
    char string[MAXIMUM_INPUT_STRING_LENGTH];
    struct human humans[MAXIMUM_HUMANS];

    FILE *fin = fopen("data.txt", "r");

    if (fin == NULL) {
        fprintf(stderr, "Cannot open file\n");
        exit(1);
    }

    int population; // after loop, this contains total body count

    for (population = 0; fgets(string, MAXIMUM_INPUT_STRING_LENGTH, fin); population ++) {
        initialize_human(string, &humans[population], dlim, end);
    }

    printf("population: %d\n", population);
    printf("last added: %s who weighs %f\n", humans[population - 1].surname, humans[population - 1].weight);  // test if we loaded it up correctly

    fclose(fin);

    return 0;
}