Problems with binary search tree in C

Question

Now reinstating my post more clearly (this is a continuation of my previous question). In the code, I try to create a binary search tree and insert elements into it. They must be saved in .txt. file. As soon as the executor says that . exe has stopped working. When I comment the insert method in main, it runs good. When debugging it accuses Segmentation fault in p->id = 1. I can’t fix it. Follow my code:

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

#define MAX_NOME 50

typedef struct politico{
   int id;
   char* nome;
   char* apelido;
//Partido* partido;
   char* cargo;
   float valorPropinaMensal;
   int quantidadeVezes;

   struct politico* esq;
   struct politico* dir;

}Politico;

   Politico* criarP(int id, char* nomeCompleto, char* apelido, char* cargo, float valor, int qtdDeVezes) {

      Politico* politico = (Politico*)malloc(sizeof(politico));

      politico->id = id;

      politico->nome = malloc(MAX_NOME * sizeof(char));
      strcpy(politico->nome, nomeCompleto);
      politico->apelido = malloc(MAX_NOME * sizeof(char));
      strcpy(politico->apelido, apelido);
      politico->cargo = malloc(MAX_NOME * sizeof(char));
      strcpy(politico->cargo, cargo);
      //no->partido = malloc(MAX_NOME * sizeof(char));
      //strcpy(no->partido, partido);
      politico->valorPropinaMensal = valor;
      politico->quantidadeVezes = qtdDeVezes;
      politico->esq = NULL;
      politico->dir = NULL;

    return politico;
  }

Politico* inserirPoliticos(Politico* raiz, int id, char* nome, char* apelido, char* cargo, float valor, int qtdDeVezes){

   Politico* novo = criarP(id , nome, apelido, cargo, valor, qtdDeVezes);
   if(raiz == NULL) return novo;

   Politico* no = raiz;
   Politico* pai = NULL;
   while(no != NULL){
      pai = no;
      if(novo->id < no->id) no = no->esq;
      else no = no->dir;
  }

   if(pai->id > novo->id) pai->esq = novo;
   else pai->dir = novo;

   return raiz;
}

int main(){
   Politico* p = NULL;

   FILE* pEscrita = fopen("politicos.txt","w");

   p->id = 1;
   p->nome="sdwwfw";
   p->apelido="sdvdsvs";
   p->cargo="asasa";

   p->valorPropinaMensal=22.0;
   p->quantidadeVezes= 2;

   p = inserirPoliticos(p, p->id, p->nome, p->apelido, p->cargo, p->valorPropinaMensal, p->quantidadeVezes);

   fprintf(pEscrita,"%d;%s;%s;%s;%.2f;%d", p->id, p->nome, p->apelido, p->cargo, p->valorPropinaMensal, p->quantidadeVezes);

   fclose(pEscrita);
   return 0;
}

Answer 1

Look at this:

Politico* p = NULL;
p->id = 1;

If p is NULL, it is obvious that p->id = 1; will give a crash.

Let’s see what you try to do:

1. In the main you try to create (incorrectly) a Politico.
2. You take all the data from this Politico and passes them one by one to the function inserirPoliticos.
3. In function inserirPoliticos, the function criarP is called.
4. In function criarP, a new Politico is mounted again with the same data.

Anyway, you ride the politician, disassemble and reassemble. That’s not very efficient. So there are two possible approaches:

1. You ride the politician on main and the passage to inserirPoliticos which only inserts a Politico already assembled.

2. You pass the raw data to the inserirPoliticos and lets inserirPoliticos mount the structure Politico when calling criarP.

I think the first approach is cleaner, by avoiding having to pass a lot of parameters referring to the same thing in several different functions. As such, its function inserirPoliticos gets like this:

Politico* inserirPoliticos(Politico* raiz, Politico *novo) {
    if (raiz == NULL) return novo;

    Politico* no = raiz;
    Politico* pai = NULL;
    while (no != NULL) {
        pai = no;
        if (novo->id < no->id) {
            no = no->esq;
        } else {
            no = no->dir;
        }
    }

    if (pai->id > novo->id) {
        pai->esq = novo;
    } else {
        pai->dir = novo;
    }

    return raiz;
}

And with that, the criarP is used in function main:

int main() {
    Politico *novo = criarP(1, "sdwwfw", "sdvdsvs", "asasa", 22.0, 2);
    Politico *raiz = inserirPoliticos(NULL, novo);

    FILE* pEscrita = fopen("politicos.txt", "w");
    fprintf(pEscrita, "%d;%s;%s;%s;%.2f;%d", p->id, p->nome, p->apelido, p->cargo, p->valorPropinaMensal, p->quantidadeVezes);

    fclose(pEscrita);
    return 0;
}