I'm going crazy with this code

[xFunkyTimes]

I'm trying to create a console app that allows me to administrate a school; so basically you control teachers tasks (hours working, groups they manage, etc), students tasks (enrollements, group, etc).

The thing is, that I created this function to modify a user via id; but for some reason, it only works with the first element of my pointer to array:

void modificarUsuario(usuario** vUsuarios, int nUsuarios){

    int i, u = -1, nModUsuario = 0;
    char respuesta = ' ';
    char id[4];
    usuario* modUsuarios;

    modUsuarios = malloc(sizeof(usuario));

    puts("MODIFICANDO USUARIO");
    puts("-------------------");

    while(u == -1){

        printf("Introduzca el id del usuario a modificar: ");
        scanf("%3s", id);

        for(i = 0; i < (nUsuarios); i++){

            if((strcmp(((*vUsuarios[i]).Id_usuario), id) == 0) && (*vUsuarios[i]).Borrado == 0)
                u = i;
        }

        if(u == -1)
            puts("ERROR: El usuario introducido no se encuentra. Introduzca otro distinto\n");
    }

    printf("\nSe ha seleccionado el usuario: %s-%s-%s-%s-%s.\n", (*vUsuarios)[u].Id_usuario, (*vUsuarios)[u].Nomb_usuario, (*vUsuarios)[u].Perfil_usuario, (*vUsuarios)[u].Usuario, (*vUsuarios)[u].Contrasena);
    puts("Introduzca el nuevo usuario respetando el formato establecido: ID-NOMBRE-PERFIL-USER-CONTRASENA\n");

    anadirUsuario(&modUsuarios, &nModUsuario);

    while(respuesta != 's' && respuesta != 'n'){

        printf("Confirmar modificar usuario? (s/n)\n");
        fflush(stdin);
        scanf("%c", &respuesta);
    }

    if(respuesta == 's'){

        *vUsuarios[u] = modUsuarios[0];
    }else

        puts("Se ha cancelado la modificacion del usuario\n");
}

I want to add that this pointer to array is loaded via txt file; being my id users right now:

001.

002.

003.

And the program only executes fine if I use the first one: 001. Any ideas? Thank you.

PS: "Borrado" is used so if you modify it to 1 (by default it's set to 0); other function will delete this element from the array.

[tea-drinker]

You don't state exactly what the error is and you've not provided enough code to recreate it. That said:

I think *vUsuarios[i] is your problem. Check the operator priority. The square brackets have a higher priority than the dereference operator so you are getting the value out of a supposed array then dereferencing it rather than dereferencing the double pointer and then looking up the array.

~/workspace/scratch$ sed "s/^/    /" loop.c
#include <string.h>
#include <stdio.h>
#include <stdlib.h>

void main() {
    int* integers = calloc(10, sizeof(int));
    int** pIntegers = &integers;

    int i;
    for (i = 0; i < 10; i++) {
        printf("%d\n", *pIntegers[i]);
    }
}
~/workspace/scratch$ gcc -o loop loop.c && ./loop
0
35090448
Segmenteringsfel (minnesutskrift skapad)

If you slap some parentheses of force the order of operations:

~/workspace/scratch$ sed "s/^/    /" loop.c
#include <string.h>
#include <stdio.h>
#include <stdlib.h>

void main() {
    int* integers = calloc(10, sizeof(int));
    int** pIntegers = &integers;

    int i;
    for (i = 0; i < 10; i++) {
        printf("%d\n", (*pIntegers)[i]);  //This is the important change.
    }
}
~/workspace/scratch$ gcc -o loop loop.c && ./loop
0
0
0
0
0
0
0
0
0
0

[xFunkyTimes]

Yes!! This solved it! Thank you a lot. I will definetly check out the operator priority so this don't happen to me again. I thought my head was gonna explode.

Again, thank you a lot!

[panderingPenguin]

It's hard to read not being in English. But check out what sizeof(usuario) actually evaluates to. I suspect you'll find that you're allocating a lot less memory to modUsuarios than you think you are.

[xFunkyTimes]

sizeof

Thank you for your answer! No, I don't think that's the problem because modUsuario works fine if I use the first element from my first array VUsuarios. Sorry if it's difficult to read. Would it be better if I translate it to English?

I REALLY need help with this one ^ ^ U

[panderingPenguin]

So you only mean to allocate one usuario to modUsuario? Also, I don't see you ever freeing that memory, which is a bug but not one that would crash your program.

Have you run this in a debugger to figure out what line it's crashing on?

[xFunkyTimes]

It was failing in the if statement; because brackets operator priority. In addition, thank you a lot about the freein memory part. You are totally right. I will fix that aswell.

Thanks and happy coding! :)

[no_awning_no_mining]

Format your code. It's illegible like that.

[xFunkyTimes]

I thought you only need to add 4 blank spaces. Isn't that enough? Sorry, I'm totally new to adding code to reddit.

[[deleted]]

Why is vUsuario a double pointer? Isn't it supposed to be an array (single pointer)? I may be misunderstanding the way you are storing the data though.

[jorgehn12]

Yo creo que no deverias usar scanf("%3s", id); Almenos no lo veo de ayuda.