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I need to make a program that, at first, read a matrix from a text file and put it on memory. I was able to do so, but when I try to close files with matrix with 4 lines or more it gives the error: * Error in `./threads': corrupted double-linked list: 0x0000000001b4e240 * the code to read the file is:

    void leitura_matriz1 ()
{
    char linha_s[MAX_LINHA];
    char *buffer;

    // leitura da primeira matriz
    FILE * matriz1_file;
    matriz1_file = fopen ("in1.txt","r");
    if (matriz1_file == NULL)
    {
        printf ("Erro na abertura do arquivo\n");
        exit(1);
    }

    // número de linhas
    fgets(linha_s, MAX_LINHA, matriz1_file);
    buffer = strtok(linha_s, " =");
    buffer = strtok(NULL, " =");
    linhas_mat1 = atoi(buffer);

    // número de colunas
    fgets(linha_s, MAX_LINHA, matriz1_file);
    buffer = strtok(linha_s, " =");
    buffer = strtok(NULL, " =");
    colunas_mat1 = atoi(buffer);

    // aloca espaço para a matriz
    matriz1 = (int**) malloc(linhas_mat1 * sizeof(int));
    if (matriz1 == NULL)
    {
        printf("erro memória");
        exit(1);
    }
    int lin, col;
    for (lin = 0; lin < linhas_mat1; lin++)
    {
        matriz1[lin] = (int*) malloc(colunas_mat1 * sizeof(int));
        if (matriz1[lin] == NULL)
        {
            printf ("erro memória 2");
            exit(1);
        }
    }

    // lê os valores do arquivo e coloca na matriz em memória
    for (lin = 0; lin < linhas_mat1; lin++)
    {
        fgets(linha_s, MAX_LINHA, matriz1_file);
        buffer = strtok(linha_s, " ");
        for (col = 0; col < colunas_mat1; col++)
        {
            matriz1[lin][col] = atoi(buffer);
            buffer = strtok(NULL, " ");
        }
    }

    fclose (matriz1_file);  
}

the file format is this:

LINHAS = 4
COLUNAS = 3
5 5 5
5 5 5
5 5 5
5 5 5

LINHAS is lines and COLUNAS columns I have never got error in closing a file when it is still opened. and it only happens if the file has more than 3 lines (4 or more lines). someone knows what it might be?

Mark Wilkins
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Erik Scheffer
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1 Answers1

2

The first allocation is not correct. Rather than:

matriz1 = (int**) malloc(linhas_mat1 * sizeof(int));

It should be:

matriz1 = (int**) malloc(linhas_mat1 * sizeof(int*));

The exception message (8 bytes) seems to indicate a 64-bit application, so pointers would be 8 bytes while sizeof(int) might only be 4 bytes. This would result in a memory overwrite while filling the array.

Mark Wilkins
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  • thank you very much. this seems to be the problem. it's my first time making a C program in a 64-bits OS, so this method always worked before. – Erik Scheffer May 02 '13 at 23:41