very strange passing of arguments

Hi everyone,

something very strange is happening in a very simple code;
specifically, I have this function:

Code:

---

void flinspace(float vmin, float vmax, int n, float *VECT)
{
        //!!! VECT must be allocated starting from 1 for this function to work properely
       
        int i;
        float dv;
       
        // WARNING NOTE THIS PRINTING LINE!!!
        //printf("vmin = %f  vmax =%f\n", vmin, vmax);
       
        VECT[1] = vmin;
        for (i=2; i<=n; i++){
                dv = (vmax - vmin)/(n-1);
                VECT[i] = VECT[i-1] + dv;
        }

return;
}

---

now, this function is called by a main function that passes the correct arguments to it as expected. However, here is the very strange behavior:

although argument 1 and 2 (float vmin, float vmax) are not supposed to be modified within this function, once I comment the "printf" line above (see WARNING NOTE above), vmin and vmax ARE in fact modified randomly within this function, and are returned to the calling function with a different value from what they were assigned;
on the other hand, when I UNcomment the print line, everythign stands still, and the only variable that is returned with a new value is the expected/wanted VECT.

Is anyone able to help me understand how this is possible?
I am on a Mac OSX 10.5 with GCC 4.0.1

Thank you in advance

You're trashing your memory somewhere else, and you're seeing the side effect of that here. Make a small program with just this function, fix your math again, and it will work fine.

Code:

---

void flinspace(float vmin, float vmax, int n, float *VECT)
{
    int i;
    float dv;

    VECT[0] = (vmax-vmin);
    VECT[1] = VECT[0] + ((vmax - vmin) / 2);
}
...
float vector[2] = { 1.0, 2.0 }; /* whatever */
...
flinspace( .75, .33, /* not used */ 0, vector );

---

Something like that. I don't know what you're planning on passing, but I don't see that you really need a loop there. Anyway, you're probably trashing your memory some place else.


Quzah.

Hi, thanks for replying and trying to help.

I indeed freed some memory from space that was not allcoated. I was allocating certain previous arrays with npts elements without noticing that npts was never assigned beforehand.

Thank you again; It was too strange to be real!