glibc detected free(): invalid next size (fast)

Question

This code generates random numbers and then produces a histogram based on input to the functions regarding the intervals. "bins" represents the histogram intervals and "bin_counts" holds the number of random numbers in a given interval.

I've reviewed several of the posts dealing with similiar issues and I understand that I'm out of bounds in the memory somewhere but GBD only points me to the "free(bins);" at the end of the code. I've double-checked my array lengths and I think they are all correct in terms of not accessing elements that don't exist/writing to memory not allocated. The weird thing is that the code works as intended, it produces an accuarate histogram, now I just need helping cleaning up this free() invalid next size error. If anybody has any suggestions I would be much obliged. The whole output is :

glibc detected ./file: free(): invalid next size (fast): 0x8429008

followed by a bunch of addresses in memory, seperated by Backtrace and Memory Map. The Backtrace only points me towards line 129, which is "free(bins);". Thanks in advance

    #include "stdio.h"
    #include "string.h"
    #include "stdlib.h"

    void histo(int N, double m, double M, int nbins, int *bin_counts, double *bins);

     int main(int argc, char* argv[])
     {

     int *ptr_bin_counts;
     double *ptr_bins; 

     histo(5,0.0,11.0,4, ptr_bin_counts, ptr_bins);

     return 0;
     } 

     void histo(int N, double m, double M, int nbins, int *bin_counts, double *bins)
     {

     srand(time(NULL));
     int i,j,k,x,y;
     double interval;
     int randoms[N-1];
     int temp_M = (int)M;
     int temp_m = (int)m;
     interval = (M-m) /((double)nbins);


     //allocating mem to arrays
     bins =(double*)malloc(nbins * sizeof(double));
     bin_counts =(int*)malloc((nbins-1) * sizeof(int));

     //create bins from intervals
     for(j=0; j<=(nbins); j++)
     {
            bins[j] = m + (j*interval); 
     } 

      //generate "bin_counts[]" with all 0's
      for(y=0; y<=(nbins-1); y++)
       {
         bin_counts[y] = 0; 
       }


      //Generate "N" random numbers in "randoms[]" array
      for(k =0; k<=(N-1); k++)
      {
          randoms[k] = rand() % (temp_M + temp_m);
          printf("The random number is %d \n", randoms[k]);
      }

       //histogram code 
       for(i=0; i<=(N-1); i++)
        {
         for(x=0; x<=(nbins-1); x++)
         {
              if( (double)randoms[i]<=bins[x+1] && (double)randoms[i]>=bins[x] )
               {
                    bin_counts[x] = bin_counts[x] + 1; 
               }
         }
         }
         free(bins);
         free(bin_counts);
         }

Answer 1

bins =(double*)malloc(nbins * sizeof(double));
bin_counts =(int*)malloc((nbins-1) * sizeof(int));

//create bins from intervals
for(j=0; j<=(nbins); j++)
{
    bins[j] = m + (j*interval); 
} 

//generate "bin_counts[]" with all 0's
for(y=0; y<=(nbins-1); y++)
{
    bin_counts[y] = 0; 
}

You are overstepping your arrays, you allocate place for nbins doubles but write to nbins+1 locations, and use nbins locations for bin_counts but have only allocated nbins-1.