Thread: I get this error Segmentation fault in my program when I run it, and I don't know why

This is the whole thing
I attached the driver also main program that I was trying to create the algorithm.

Code:

 / Driver

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <math.h>
#include <getopt.h>
#include <sys/time.h>

/* getopt.h */
extern char *optarg;

/* stdlib.h */
extern void srand48(long seed);
extern double drand48(void);

/* this function is implemented in cntSort.c */
extern void cntSort(unsigned m, unsigned n, unsigned data[]);

/* comparison function for qsort() */
static int cmpUnsigned(const void *a, const void *b)
{
return *(unsigned *)a - *(unsigned *)b;
}

int main(int argc, char* argv[])
{
unsigned m, n, *data, *qsorted, i;
struct timeval start, stop;
float msec;
long seed;
int c;

/* command line options
* ./cntSort -m mValue -n nValue -s seedValue
* m default 64
* n default 2^20, 1M
* seed default 2018
*/
m = 64;
n = 1 << 20;
seed = 2018;
/* process optional command line arguments */
while ((c = getopt(argc, argv, "m:n:s:")) != -1) {
switch (c) {
case 'm': sscanf(optarg, "%u", &m); break;
case 'n': sscanf(optarg, "%u", &n); break;
case 's': sscanf(optarg, "%ld", &seed); break;
default: break;
}
}
printf("m %u, n %u, seed %ld\n", m, n, seed);

/* seeding the pseudorandom number generator */
srand48(seed);

/* allocate memory -- remember to free up them later */
data = (unsigned *)malloc(sizeof(unsigned) * n);
qsorted = (unsigned *)malloc(sizeof(unsigned) * n);

/* initialize data */
for (i = 0; i < n; i++)
qsorted[i] = data[i] = (unsigned) floor(drand48() * m);

/* time qsort */
gettimeofday(&start, NULL);
qsort((void *)qsorted, n, sizeof(unsigned), cmpUnsigned);
gettimeofday(&stop, NULL);
msec = (stop.tv_sec - start.tv_sec) * 1000 +
(stop.tv_usec - start.tv_usec) / 1000;
printf("quicksort takes %.2f msec\n", msec);

/* time cntSort */
gettimeofday(&start, NULL);
cntSort(m, n, data);
gettimeofday(&stop, NULL);
msec = (stop.tv_sec - start.tv_sec) * 1000 +
(stop.tv_usec - start.tv_usec) / 1000;
printf("cntSort takes %.2f msec\n", msec);

/* verify cntSort works correctly */
for (i = 0; i < n; i++)
if (data[i] != qsorted[i]) {
fprintf(stderr, "data differs from qsorted at the %u-th element\n", i);
exit(1);
}
/* free up memory */
free(qsorted);
free(data);

return 0;
}

Code:

 / Main program to create the algorithm

#include <stdlib.h>

void cntSort(unsigned m, unsigned n, unsigned data[])
{
unsigned *count;

/* allocate memory */
count = (unsigned *)malloc(sizeof(unsigned) * m);

/* free up memory */
free(count);
}

Originally Posted by jimblumberg

Let's start by having you post the entire program, not just a few bits and pieces.

Next do you know how to print that data[] array? If so show us a program that prints that array.

I attached the whole program

Okay so now since cntSort() is really not doing anything are you still getting a segmentation fault?

If so where does your debugger tell you the problem shows itself?

The driver code is given from the prof, I cannot touch anything there the problem I'm having is with main.c

./cntSort -m 64 -n 1048676 -s2018

Without anything on it doesn't show any problems, I just don't know what's going on with the algorithm I created above and have no time I have to turn it in tomorrow

Originally Posted by erald23

./cntSort -m 64 -n 1048676 -s2018

Without anything on it doesn't show any problems, I just don't know what's going on with the algorithm I created above and have no time I have to turn it in tomorrow

You completely deleted all the code, so saying you "created an algorithm" is ... not true. You posted a text description of the algorithm in that one post of yours; you just need to implement it.

If you are still referring to your original code way back in post one, the algorithm you created there is:

1. Use un-initialized data for the count (rather than setting the initial counts to zero)
2. Process a complete set of garbage data (temp) that was grabbed for no reason whatsoever
3. Process the actual data (but on top of the nonsense counts that were already there)
4. Erase the good data by copying the garbage data (temp) on top of it, completely ignoring the count information (that was completely wrong anyway)

Hopefully you can see why that algorithm doesn't actually solve your problem.

Originally Posted by tabstop

You completely deleted all the code, so saying you "created an algorithm" is ... not true. You posted a text description of the algorithm in that one post of yours; you just need to implement it.

If you are still referring to your original code way back in post one, the algorithm you created there is:

1. Use un-initialized data for the count (rather than setting the initial counts to zero)
2. Process a complete set of garbage data (temp) that was grabbed for no reason whatsoever
3. Process the actual data (but on top of the nonsense counts that were already there)
4. Erase the good data by copying the garbage data (temp) on top of it, completely ignoring the count information (that was completely wrong anyway)

Hopefully you can see why that algorithm doesn't actually solve your problem.

First of all I said before I'm new at C programming and that's why I'm asking help , but if you not willing to help or give me at least recommendation, dont do it at all.
I understand you guys are experts but I'm sure you started like me at some point.
Thanks

Originally Posted by erald23

First of all I said before I'm new at C programming and that's why I'm asking help , but if you not willing to help or give me at least recommendation, dont do it at all.
I understand you guys are experts but I'm sure you started like me at some point.
Thanks

There's nothing wrong with being new; there's all sorts of things wrong with not even trying to learn -- and by the evidence you're showing here, this is where you are. Your first code was an attempt to solve the problem with lots of problems with it, that have been pointed out. Your response was to erase everything and wait for us to give you the answer. You have a list of all the things that were wrong with your original code; you have a list of the things you need to do (which we didn't even give you, that you already had yourself). If there's something specific about the list that you want to ask about, then do so, but you need to sit down and do those things.

Just to take a particular example, the thing that's been brought up the most is "setting all the initial counts to zero". The only thing I can see that might be considered an attempt to do so in your own code is

Code:

count[i];

from your second code posting. If that was really an attempt to set everything to zero, then you are a very long way from where you need to be and you need to review a lot of material. If that wasn't an attempt at this, then (a) why is it there and (b) why haven't you tried to set all your initial counts to zero?

(For reference so you can see the difference, setting everything equal to zero looks like

Code:

for (int i = 0; i < whichever_of_n_or_m_you_are_using_for_this_which_is_why_you_use_real_variable_names; i++) {
    count[i] = 0;
}

We try to just not hand out homework answers here, but the point I'm trying to make is that each of these steps is pretty darn simple.)

Originally Posted by tabstop

There's nothing wrong with being new; there's all sorts of things wrong with not even trying to learn -- and by the evidence you're showing here, this is where you are. Your first code was an attempt to solve the problem with lots of problems with it, that have been pointed out. Your response was to erase everything and wait for us to give you the answer. You have a list of all the things that were wrong with your original code; you have a list of the things you need to do (which we didn't even give you, that you already had yourself). If there's something specific about the list that you want to ask about, then do so, but you need to sit down and do those things.

Just to take a particular example, the thing that's been brought up the most is "setting all the initial counts to zero". The only thing I can see that might be considered an attempt to do so in your own code is

Code:

count[i];

from your second code posting. If that was really an attempt to set everything to zero, then you are a very long way from where you need to be and you need to review a lot of material. If that wasn't an attempt at this, then (a) why is it there and (b) why haven't you tried to set all your initial counts to zero?

(For reference so you can see the difference, setting everything equal to zero looks like

Code:

for (int i = 0; i < whichever_of_n_or_m_you_are_using_for_this_which_is_why_you_use_real_variable_names; i++) {
    count[i] = 0;
}

We try to just not hand out homework answers here, but the point I'm trying to make is that each of these steps is pretty darn simple.)

Thanks very much for trying to help even myself don't want you to put the answer because I want to learn. I just want to be directed in the right way since the professor doesn't offer that much help. anyways thanks again

One thing that can help us help you out is putting in comments in the code you've written as to what you are trying to do with each chunk of code. For that matter, in this case since you have a description of what's going on you can even start with the comments, and then write the code to match.

Code:

//Create space to hold the counts, and initialize to zero
count = malloc( ... );
for (int i = 0 ...) {
    count[i] = 0;
}

//Go through data array, and count as we go

//Use counts to write out data in sorted order

//Clean up

Your original code did have the proper walk-through-the-data-and-add-to-count loop, so that chunk is definitely salvageable.