scanf confusion

[KBriggs]

Hey all, another question for you.

I have an input file consisting of three columns of double values representing x,y,z coordinates. I need to read them into an array. Now, my code works, but the compiler complains that I don't check the return value from fscanf - just a warning, the code still runs fine. But I tried to rewrite to check the return value anyway. It seems to read the values in fine, but when I go to reprint the array to check, all the values are 0. Any idea why?

Here is the working code. The printf both inside and outside the loop print the same thing.

for (i = 0; i < N_part; i++)
  {
    fscanf(particleList,"%lf%lf%lf", &particleMatrix[i][0], &particleMatrix[i][1], &particleMatrix[i][2]);
    printf("%f\t%f\t%f\n",particleMatrix[i][0], particleMatrix[i][1], particleMatrix[i][2]);
    if (particleMatrix[i][0] * particleMatrix[i][0] + particleMatrix[i][1] * particleMatrix[i][1] + particleMatrix[i][2] * particleMatrix[i][2] > maxRadiusSquared)
    { 
      maxRadiusSquared = particleMatrix[i][0] * particleMatrix[i][0] + particleMatrix[i][1] * particleMatrix[i][1] + particleMatrix[i][2] * particleMatrix[i][2];
    }
  }  
  maxRadius = sqrt(maxRadiusSquared);//Radius of the cluster

for (i = 0; i < N_part; i++)
{
   printf("%f\t%f\t%f\n",particleMatrix[i][0], particleMatrix[i][1], particleMatrix[i][2]);
}

Here is the nonworking code - the inside printf prints what it should, but the one outside prints 0's.

while (fscanf(particleList,"%lf%lf%lf", &particleMatrix[i][0], &particleMatrix[i][1], &particleMatrix[i][2]) != EOF)
  { 
    maxRadiusSquared = particleMatrix[i][0] * particleMatrix[i][0] + particleMatrix[i][1] * particleMatrix[i][1] + particleMatrix[i][2] * particleMatrix[i][2];
    printf("%f\t%f\t%f\n",particleMatrix[i][0], particleMatrix[i][1], particleMatrix[i][2]);
  }


  maxRadius = sqrt(maxRadiusSquared);

for (i = 0; i < N_part; i++)
{
   printf("%f\t%f\t%f\n",particleMatrix[i][0], particleMatrix[i][1], particleMatrix[i][2]);
}

I am sure I am just using fscanf wrong in the second one, but how?

[tabstop]

You could change i at some point, if you want to move forward in the array.

[MK27]

What is the initial value of "i" in the while loop in the non-working example? And subsequently?

[aside] this is an interesting hybrid of the "mk27" and "allman" indentation styles Now I understand why I am losing in the pole...

[dwks]

Also, I'd suggest a

#define SQUARE ((x) * (x))

or

double square(double number) {
    return number * number;
}

and an intermediate variable to shorten that really long radius-square expression calculation.

With your second version, you should probably also record how many particles you read (how high i becomes, once you start incrementing it as per tabstop's post!), instead of looping up until N_part.

[KBriggs]

Hahahaha wow, what a dumb mistake. I am so used to using for loops that I competely forgot the increment step in the while loop. Lol...

Thanks for the tips, but in comparison to other parts of the code, that part takes less than 0.1% of the runtime, so making that faster won't really do anything.

And yeah, sorry about the indentation, I ended up adding a few things afterward and just added them here instead, so the indentatin got messed up. My code looks prettier, honest!

[laserlight]

I am so used to using for loops that I competely forgot the increment step in the while loop.

I suggest that you use a for loop, but incorprate the check of fscanf's return value with the i < N_part condition.

[KBriggs]

You mean:

for (i = 0; i < N_part && fscanf(particleList,"%lf%lf%lf", &particleMatrix[i][0], &particleMatrix[i][1], &particleMatrix[i][2]) != EOF; i++)
  { 
    maxRadiusSquared = particleMatrix[i][0] * particleMatrix[i][0] + particleMatrix[i][1] * particleMatrix[i][1] + particleMatrix[i][2] * particleMatrix[i][2];
    printf("%f\t%f\t%f\n",particleMatrix[i][0], particleMatrix[i][1], particleMatrix[i][2]);
  }

[laserlight]

You mean:

Yeah, though if I were you, I would define:

int readParticle(FILE *file, double particle[3])
{
    return fscanf(file, "%lf%lf%lf", &particle[0], &particle[1], &particle[2]);
}

void printParticle(FILE *file, double particle[3])
{
    fprintf(file, "%f\t%f\t%f\n", particle[0], particle[1], particle[2]);
}

double computeMaxRadiusSquared(double particle[3])
{
    return particle[0] * particle[0]
        + particle[1] * particle[1]
        + particle[2] * particle[2];
}

Then write:

for (i = 0; i < N_part && readParticle(particleList, particleMatrix[i]) != EOF; ++i)
{
    maxRadiusSquared = computeMaxRadiusSquared(particleMatrix[i]);
    printParticle(stdout, particleMatrix[i]);
}

I assume that you will actually do more with maxRadiusSquared than assign to it on each iteration of the loop.

[KBriggs]

Yeah, it becomes a parameter for other functions through the program, all this stuff is just initializing. Thanks for the tips, I suppose it couldn't hurt to break the program up a little more, right now each function does quite a bit of stuff.

That should actually be

if (maxRadiusSquared > currentMaxRadius)
{
maxRadiusSquared = currentMaxRadius;
}
but since my list is sorted right now it is irrelevent. I had that elsewhere... I must have removed it when I redid the loop and forgot to put it back. Thanks.