[SOLVED] C program. error: *** glibc detected *** ./proyecto: malloc(): memory corruption

Carlos2313 · 10-24-2010, 03:30 PM

I was working in this program. It's supposed to calculate the poisson Table. however It has to stop when the result is 1. It is not stopping, so it's giving me the previous error.

void PoissonTable(){
int current=0;
PoissonArr = (float*) malloc (sizeof(float)*10);
float store=0;
while(store < 1 )
{

PoissonArr[current] = Poisson(current);

if(current != 0)
PoissonArr[current] += PoissonArr[current-1];

store = PoissonArr[current];

printf("store %f\n",store);

if(store >= 1)
break;

current++;
}

}
The question is: How can I stop the program if in the cycleI'm already defining that it should stop when the result equals or is bigger than 1??
Thank you !!

johnsfine · 10-24-2010, 04:14 PM

You should learn to use CODE tags to post readable code.

Quote:

Originally Posted by Carlos2313

It is not stopping, so it's giving me the previous error.

I don't think you have posted the right information to let us diagnose the problem.

Code:

while(store < 1 )

Code:

if(store >= 1)
     break;

Quote:

How can I stop the program if in the cycleI'm already defining that it should stop when the result equals or is bigger than 1??

I assume you added a second way to break out of the loop (making the first way redundant) because you didn't think the first one was working.

So you seem to have some mental model of what is happening in your code (that store reaches 1 or higher and the loop keeps going). But you don't seem to really know what is happening. You could use a debugger, or add some temporary printouts, or add some "defensive programming". Any of those is better than guessing.

Code:

PoissonArr = (float*) malloc (sizeof(float)*10);

...

Code:

current++;

For example, defensive programming might follow current++; with

Code:

if (current >= 10 ) {
   printf("Exceeded size of array.  Aborting.\n");
   exit(-1);
}

Maybe a bit drastic (exit instead of return) but you get the idea.

Carlos2313 · 10-24-2010, 04:22 PM

yeap, that's true

..... This is the output I got:

store 0.122456
store 0.379615
store 0.649631
store 0.838643
store 0.937874
store 0.979551
store 0.994138
store 0.998514
store 0.999663
store 0.999931
store 0.999987
store 0.999998
store 1.000000
store 1.000001
*** glibc detected *** /media/NYU/SO
proyect: malloc(): memory corruption: 0x0804c0b8 ***

According the information I have the variable store has the correct result.. However I just don't get it ... I don't know why the program is not stopping

hehe, yes, I think that I am going to have to use that solution... Otherwise the program won't stop

Quote:

if (current >= 10 ) {
printf("Exceeded size of array. Aborting.\n");
exit(-1);
}

Thank you so much !!!

johnsfine · 10-24-2010, 04:42 PM

What about just making the array big enough?

Quote:

Originally Posted by Carlos2313

..... This is the output I got:

store 0.122456
store 0.379615
store 0.649631
store 0.838643
store 0.937874
store 0.979551
store 0.994138
store 0.998514
store 0.999663
store 0.999931
store 0.999987
store 0.999998
store 1.000000
store 1.000001

You allocated room for 10 values.

The 13'th value was very close to 1. It was so close that printf rounded it to 1. But it was less than 1. It probably is the value that would have been 1 if you were computing with infinite precision. Welcome to floating point. It isn't infinite precision.

Then the 14'th value was more than 1 and your loop stopped, just as you programmed it to.

By then you have stored 14 values into an array allocated for 10.

It may be surprising (but a programmer better learn this early) that storing 14 values where there was room for only 10 typically does not crash right at the place the bad stores occur. Typically it crashes later. In complicated code it usually crashes in an obscure way with no obvious connection to the bad stores. In a program this simple it often crashes (as it did for you) in the malloc code either releasing the chunk that was exceeded or the next time you allocate another chunk.

Carlos2313 · 10-24-2010, 04:56 PM

You are so right ! Thank you so much... I don't know how I could not see that

I really appreciate your help