Populating a dynamic array of structs

Question

I'm trying to write a program that will create a database made of entries (reg), the amount of which is set by the user at runtime. My idea was to make a type struct dynamic array to store my entries but I'm having a hard time storing the values in the array, I've tried direct assignment but that didn't work, as soon as I type in the first value the program crashes, I looked into it and most people seem to use a dedicated function to insert elements into the array, but I'm having a hard time understanding how to go about it.

typedef struct
{
    char nome[60];
    char morada[60];
    char codigop[60];
    char telefone[20];
    char aniver[20];
    char sexo;
    char prof[60];
    float altura;
    long contribuinte;
} reg;

// array of structs
typedef struct
{
    reg *array;
    size_t used;
    size_t size;
} Array;

//crashes
void Populador(int tamanho, reg * a){
    char nomed[60];
    for (int i = 0; i < tamanho; i ++){
        printf("Quais os dados do %d registo? \n ", i+1);
        printf("Lembrete, a ordem e: nome, morada, codigo postal, telefone, "
               "data de nascimento, genero, profissao, altura, contribuinte. \n");
        scanf(" %s", &a[i].nome);
        scanf(" %s", a[i].morada);
        scanf(" %s", a[i].codigop);
        scanf(" %s", a[i].telefone);
        scanf(" %s", a[i].aniver);
        scanf(" %c", a[i].sexo);
        scanf(" %s", a[i].prof);
        scanf(" %f", a[i].altura);
        scanf(" %long", a[i].contribuinte);
    }
}

int main() {
    int option;
    char key[60], read[20], write[20];
    int tamanho; //size
    char number[20];
    Array a = { 0 };
    printf(  "1 - Criar um nova base de dados com dimensão especificada pelo utilizador\n" //create new data base
             "2 - Guardar a base de dados existente num ficheiro de texto\n"
             "3 - Carregar uma base de dados a partir de um ficheiro gravado previamente\n"
             "4 - Listar toda a informacao da base de dados no ecra\n"
             "5 - Consultar um contacto a partir do seu numero \n"
             "6 – Procurar um contacto a partir do nrº de contribuinte \n"
             "7 - Listar todos os contactos cujo nome contém um nome/palavra inserido pelo utilizador \n"
             "8 – Ordenar os contactos por ordem alfabetica de nome\n"
             "9 - Modificar dados de um registo \n" 
             "10 - Sair do programa \n ");

    do {
        scanf(" %d",  &option);
        switch (option) {
            case 1:
                scanf( " %d", &tamanho);
                Populador(tamanho, &a);
                break;

            case 2:
                printf(  "Qual o nome do ficheiro? /n");
                scanf(" %s", &read[20]);
                readf(read);
                break;

            case 3:
                printf(  "Qual o nome do ficheiro no qual quer guardar a base de dados?\n");
                scanf( " %s" ,&write[20]);
                writef(write);
                break;

            case 4:
                display(tamanho, &a);
                //chamar funcao display
                break;

            case 5:
                scanf(" %d",  &number);
                if( (number <= tamanho) ) {
                    search(number, &a);
                }
                break;

            case 6:
                if (searchcont(tamanho, &a) == 1){
                    printf("O contribuinte que procurou foi encontrado no indice %d \n", (searchcont(tamanho, &a)));
                }
                else
                    printf("O contribuinte que procurou nao foi encontrado na base de dados \n");
                break;

            case 7:
                searchkey(tamanho, &a, key);
                break;

            case 8:
                bubble_sort(tamanho, &a);
                //ordenar por ordem alfabetica
                break;

            case 9:
                change(&a);
                break;

            case 10:
                return 1;

            default:
                printf( "Opcao invalida\n") ;
                break;

        }
    }while(option != 10);

    return 0;
}

Sorry, added the code that crashes the program.

Chuck Norris
– Chuck Norris

2021-01-30 23:35:31 +00:00
Commented Jan 30, 2021 at 23:35 — Chuck Norris
– Chuck Norris, Commented Jan 30, 2021 at 23:35

chqrlie · Accepted Answer · 2021-01-31 00:30:53Z

2

Here is a small program to read and add entries to the database:

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

typedef struct {
    char nome[60];
    char morada[60];
    char codigop[60];
    char telefone[20];
    char aniver[20];
    char sexo;
    char prof[60];
    float altura;
    long contribuinte;
} reg;

// array of structs
typedef struct {
    reg *array;
    size_t used;
    size_t size;
} Array;

int add_entry(Array *data, const reg *e) {
    if (data->used == data->size) {
        size_t new_size = data->size + data->size / 2 + 16;
        reg *new_array = realloc(data->array, sizeof(*new_array) * new_size);
        if (new_array == NULL) {
            // failure: return error
            return -1;
        }
        data->size = new_size;
        data->array = new_array;
    }
    memcpy(&data->array[data->used++], e, sizeof(*e));
    return 0;
}

void free_entries(Array *a) {
    free(a->array);
    a->array = NULL;
    a->used = a->size = 0;
}

int Populador(int tamanho, Array *a) {
    reg e;
    int i = 0;

    while (i < tamanho) {
        printf("Quais os dados do %d registo?\n ", i+1);
        printf("Lembrete, a ordem e: nome, morada, codigo postal, telefone, "
               "data de nascimento, genero, profissao, altura, contribuinte.\n");
        if (scanf("%59s %59s %59s %19s %19s %c %59s %f %ld",
                  e.nome, e.morada, e.codigop, e.telefone, e.aniver, &e.sexo,
                  e.prof, &e.altura, &e.contribuinte) != 9) {
            int c;
            printf("invalid input\n");
            while ((c = getchar()) != EOF && c != '\n')
                continue;
            if (c == EOF)
                break;
            continue;
        }
        if (add_entry(a, &e)) {
            break;
        }
        i++;
    }
    return i;
}

int main() {
    Array a = { 0 };
    int n = Populador(10, &a);
    printf("%d entries\n", n);
    free_entries(&a);
    return 0;
}

edited Jan 31, 2021 at 0:30

answered Jan 30, 2021 at 23:38

chqrlie

152k12 gold badges145 silver badges231 bronze badges

Sign up to request clarification or add additional context in comments.

10 Comments

Daniel Walker Over a year ago

What's p? Did you mean sizeof(*e)?

chqrlie Over a year ago

@DanielWalker: p should have been new_array, sizeof(*e) is the same as sizeof(reg) but I prefer to use the type of the object pointed to by e instead of the type to avoid a potential type mismatch.

Chuck Norris Over a year ago

Hey! First of all thanks for the comment, but when I ran it again with these changes the same thing happened, it printed this line " printf("Lembrete, a ordem e: nome, morada, codigo postal, telefone, " "data de nascimento, genero, profissao, altura, contribuinte.\n");" I typed in a name and it crashed, strange.

chqrlie Over a year ago

@ChuckNorris: did you use the above code or copy part of it? Try and compile a debug build and use the debugger to see where it crashes.

Chuck Norris Over a year ago

@DanielWalker So I just oppened up a new file to test out your code and it works perfectly, but when I copy it over to my project it crashes.... I have a switch with a menu in place that calls the Populador function, do you think that might be it? I can't say I know how to work with the debugger

|

0___________ · Accepted Answer · 2021-01-30 23:38:14Z

2

IMO better way :

typedef struct
{
    char nome[60];
    char morada[60];
    char codigop[60];
    char telefone[20];
    char aniver[20];
    char sexo;
    char prof[60];
    float altura;
    long contribuinte;
} reg;

// array of structs
typedef struct
{
    size_t used;
    size_t size;
    reg data[];
} Array;


Array *allocate(Array *arr, size_t newsize)
{
    Array *newarray = realloc(arr, sizeof(*newarray) + newsize * sizeof(newarray -> data[0]));

    if(newarray)
    {
        if(arr) newarray -> used = arr -> used;
        newarray -> size = newsize;
    }
    return newarray;
}

only one allocation needed.

answered Jan 30, 2021 at 23:38

0___________

71.6k4 gold badges41 silver badges94 bronze badges

Collectives™ on Stack Overflow

Populating a dynamic array of structs

2 Answers 2

10 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

10 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related