Copying from a file to an array

Question

Good evening, I’m having a problem, I’m wanting to copy information from a file to an array that allocates dynamically, the text file contains this:

....*
*....
.....
.*...
.....

(5 rows and 5 columns that will go to the matrix I’ve allotted using realloc because I don’t know the number of rows and columns that the information inside the file has).

I need to copy this to an array, but remembering that I don’t know the file size so I have to use feof. I have a problem with segmentation and I don’t know where, and I am doubtful if the passage of the file pointer and the process within the "reading" function is being done in a correct way.Below is the code:

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

char** leitura(char* nome)//Declaracao de funcao que aloca a matriz
{
    FILE* ponteiro;
    int i = 0,j = 1, k ,l;
    char** campo = NULL;
    char carac;

    ponteiro = fopen("nome", "w");

    while(!feof(ponteiro))
    {
        i++;
        campo = (char**) realloc(campo, i * sizeof(char*));     

        while(fscanf(ponteiro, "%c", &carac) != '\n')
        {
            campo[j - 1] = (char*) realloc(campo[j - 1], j * sizeof(char));
            campo[i - 1][j - 1] = carac;
            j++;    
        }
    }

    for(k = 0; k < i; k++)
    {
        for(l = 0; l < j; l++)
        {
            printf("%c", campo[i][j]);
        }
        printf("\n");
    }

    fclose(ponteiro);

    return campo; //Retorno da matriz alocada dinamicamente
}

int main (void)
{
    int tamanho = 0, linha = 0, coluna = 0;
    char* nome = NULL;
    char** retornoCampo = NULL;
    size_t tam = 0;
    int i, j;

    int opcao = 0;

    scanf("%d", &opcao);


    switch(opcao) //Opcoes a serem escolhidas
    {
        case 1: //Leitura
            getline(&nome, &tam, stdin); //Funcao para adquirir o nome do arquivo
            nome[strlen(nome) - 1] = '\0';
            printf("%s\n", nome);
            retornoCampo = leitura(nome);

            break;
        case 2: //Inicializacao do tabuleiro
            break;
        case 3: //Acao do usuario
            break;
    }

    return 0;
}

Answer 1

1. ponteiro = fopen("nome", "w"); <== this will open the file for writing (wRite) and empty it. You must do ponteiro = fopen("nome", "r");

2. The use while(!feof(ponteiro)) is incorrect. The function feof() indicates whether the last access to stream gave error; does not indicate if the next access will fail because there is no more data available (there is no function in C that does this! ). What you should do is (try) read data normally and, if there is an error, finish the cycle. If you want you can check if the error was due to the lack of data or any other reason (network break, bad sector on disk, ...).

3. In C, do the cast to the outcome of malloc() is redundant and can hide an error that the compiler would find if it wasn’t there cast. I suggest you stop making the explicit conversion to the amounts returned by malloc() (or calloc()) and realloc().

4. while(fscanf(ponteiro, "%c", &carac) != '\n') This while goes into infinite cycle. The result of your fscanf() can only be one of three values, namely 1, 0, or EOF. Like '\n' is different from any of these values the cycle never ends. The value returned by fscanf() will be EOF if read error (end of data in file, network break, bad sector, ...); will be 1 if the fscanf() could assign a value to the variable carac and will be 0 if you could not assign value.

And for now I’m done.

Edit: Your cycle can probably be like this

    while (fscanf(ponteiro, "%c", &carac) == 1) {
        if (carac == '\n') break;
        // ...
    }