Question

I just can’t figure out how to do a malloc. The following code just types the first 5 lines and then stops, any help would be appreciated!

// Read query points from query file------------------------------
double **queryPoint;

token=(char*)malloc(40);
int qp_count=0;

i=0;
qp_count=0;
while(fgets(line,sizeof(line),queryFile)!=NULL)
{
    queryPoint=(double*)malloc(sizeof(double**));
    queryPoint[qp_count]=(double*)malloc(sizeof(double*)*2);

    printf("line:%s",line); 

    token = strtok(line," ,\t");        

    queryPoint[qp_count][0]=atof(token);        
    token = strtok(NULL, " ,\t");

    printf("l[%d]=%lf \n",qp_count,queryPoint[qp_count][0]);

    queryPoint[qp_count][1]=atof(token);
    token = strtok(NULL, " ,\t");
    printf("l[%d]=%lf \n",qp_count,queryPoint[qp_count][1]);

    qp_count++;
}

{
This is the form of the query file

9.85797 5.72533
9.58711 2.09899
2.28203 7.19344
4.49096 5.50094
6.05297 1.60751
6.19901 1.52312

}
…
30 lines total

Answer 1

Initialize at the beginning:

double **queryPoint = 0;
int qp_count = 0;

For every line call:

// call realloc to make the space for points larger by one element
queryPoint = realloc(queryPoint, sizeof(double*)*(qp_count+1));

// allocate space for the new point
queryPoint[qp_count] = malloc(sizeof(double)*2);

// increase the point count
qp_count++;

Note that you may use realloc to resize the space for lines. Also note that you should add error handling.

To free the memory you need to call:

for(int i=0;i<qp_count;i++)
    free(queryPoint[i]);

free(queryPoint);