Why am I getting "corrupted double-linked list" error?

Question

The program

I am writing a program in C that reads in a document of polynomial coefficients and can evaluate the roots of the polynomials.

In one of my functions I am attempting to read through the text file, and create a list of "polynomials". Polynomials are defined as follows:

typedef struct
{
    unsigned int nterms;       /* number of terms */
    double complex *polyCoef;  /* coefficients    */
} polynomial;

The text files are in the following format, where each line represents a polynomial and each number represents a coefficient:

1     0     0     0     2    -1
16    70  -169  -580    75
1     0     4     0    -5
0    -9     3     5    -3
5    -4     3    -2     0
1.0   -3.4    5.4531   -4.2077    1.5092   -0.2030

---

The Problem

I am getting some odd behavior in my implementation attempt. With the following code, I get

* Error in `./hw6': corrupted double-linked list: 0x0000000000a1c240 *

    PolyFile = fopen(argv[2], "r"); 

    if(NULL == PolyFile){   /* If the file fails to open */
        fprintf(stderr, "Error: Input file '%s' not found\n", argv[2]); 
        return(-1); 
    }

    /****** Read in the polynomials *************/
    polynomials = malloc(sizeof(polynomial*) * size); /* Initialize */

    if(polynomials == NULL){
        fprintf(stderr, "%s %i: Could not allocate memory\n", __FILE__, __LINE__);
        exit(-99); 
    }

    /* Read all of the data from the file */
    while(fgets(String, MAX_STR_LEN, PolyFile)) {
        strLen = strlen(String); /* Determine size of line */

   /* Ensure that the line is not too long */
        if(strLen <= MAX_STR_LEN){
            /* Create the polynomial */
            p = (polynomial*)malloc(sizeof(polynomial)); 

            token = strtok(String, " ");

            while(token){
                coefficients[coeffCount] = token; 
                token = strtok(NULL, " ");
                coeffCount++;   
            } 
            createPoly(p, coeffCount); 

            /* Set p->polyCoef to the reverse of coefficients */            
            for(int lcv = 0; lcv <= coeffCount - 1; lcv++){

                p->polyCoef[lcv] = atof(coefficients[coeffCount - lcv - 1]) + 0.00*I; 
            }
            coeffCount = 0; 

            polynomials[size] = p;
            printf("P->NTERMS: %i\n", p->nterms); 
            size++; 

        } else {
            fprintf(stderr, "%s %i: Line too long. Polynomial ignored\n",
                        __FILE__, __LINE__); 
        }

    }
    fclose(PolyFile); 
    /**************************/
    for(int j = 0; j <= size - 1; j++){
        printf("J: %i\n", j); 
        printf("IN FOR LOOP: %i\n", (polynomials[j])->nterms); 
        // printPoly(polynomials[j]); 
        printf("\n"); 
    }

. . .

/*---------------------------------------------------------------------------
  Creates a polynomial data structure with nterms.  This allocates storage
  for the actual polynomial.

  Where: polynomial *p       - Pointer to polynomial data structure to create
         unsigned int nterms - The number of elements to create
  Returns: nothing
  Errors:  prints an error and exits
---------------------------------------------------------------------------*/
void createPoly(polynomial *p, unsigned int nterms){
  int lcv; /* loop control variable */

  /* Create a polynomial struct */
  p->nterms = nterms; 
  p->polyCoef = (double complex*)malloc(sizeof(double complex)*nterms); 

  /* Error out if problem with malloc */
  if(p->polyCoef == NULL){
    fprintf(stderr, "%s %i:Error allocating memory\n", __FILE__, __LINE__); 
    exit(1); 
  }

  /* Set the coefficients to 0 */
  for(lcv = 0; lcv < nterms; lcv++){
    (p->polyCoef)[lcv] = 0.00 + 0.00*I; 
  }
}

If I remove the fclose(PolyFile);, the code continues, but debug printing shows that polynomials[0]->nterms is equal to a random, changing, very large number. I have no idea why this is happening.

Answer 1

The problem occurred because at the time of the initialization of polynomials, size was equal to 0:

polynomials = malloc(sizeof(polynomial*) * size);

This was fixed by allocating the proper size, using the number of lines in the file.