Segmentation fault on linux

[jekaterina]

Sorry that I am new to linux, I don't know how can I fix the Segmentation fault. I will be very grateful if anyone can help me.



#include <iostream>
#include <cstdlib>
#include <pthread.h>
#include <unistd.h>
#include <time.h>
#include <cstring>
#include <semaphore.h>

using namespace std;

#define NUM_THREADS 36
#define MAX 36

char matrix[6][6]; //result sheet

//queue elements
char queue[MAX], head=0, tail=0;


int row=0,col=0;
int runtime=1; // track the number of times we have run the dispatch funciton

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

void dispatch(){

row = runtime / 6;
sleep(1); //wait 1 second to generate column number
col = runtime % 6 - 1;
if (runtime % 6 == 0)
col = 5;

}


void enqueue(char c){
queue[tail] = c;
tail = (tail+1)%MAX ;
}

char dequeue(){
char temp = queue[head];
head = (head+1)%MAX ;
return temp;
}




//master thread
void *qcTask(void *args)
{
//simulate product convey delay
sleep(1);

pthread_mutex_lock(&mutex);

dispatch();

sleep(rand()%6+5);

if(rand()%100<90)
enqueue('Q');

else
enqueue('U');

pthread_mutex_unlock(&mutex);

pthread_exit(NULL);
}



int main (int argc, char* argv[])
{


int input = atoi(argv[1]);
//error handling
if(argc!=2 || input == 0 || input>36){
cout<<"Input is illegal!";
}

else{
pthread_t threads[input];


int rc, i, count = 0;

srand(time(NULL));

for(i=0;i<input;i++){

rc = pthread_create(&threads[i], NULL, qcTask, NULL);
if (rc){
cout << "Error:unable to create thread," << rc << endl;
exit(-1);

}
}

for (i = 0; i < input; i++){
rc = pthread_join(threads[i], NULL);
if (rc){
cout << "Error:unable to join," << rc << endl;
exit(-1);
}
}

//initize matrix with default value 'i'

for (int i = 0; i < 6; i++){
for (int j = 0; j < 6; j++){
matrix[i][j] = 'I';
}
}

//fill the result sheet
for(int i=0;i<6;i++){
for (int j = 0; j < 6; j++){
matrix[i][j]=dequeue();
}

}

for (int i = 0; i < 6; i++){
for (int j = 0; j < 6; j++){
cout << matrix[i][j];
if (matrix[i][j] == 'U')
count++;
}
cout << endl;
}

cout << count << " products are unqualified.";
pthread_exit(NULL);

}
}

[Peter87]

Make sure argc >= 2 before calling atoi(argv[1]).

[ne555]

http://www.cplusplus.com/forum/general/112111/

[eec]

hi
this error may occur when you pass an NULL argument to function in Linux gcc Compiler.
try to check every parameters before passing them to functions.
try this structure :
if (arg1 == NULL ){
printf("arg1 is NULL");
}
functiontest(arg1);

[eec]

I change some of your code, transform it to C, add examine it with simple example
may be helpful for you

Esmaeel E

/*
 * source_00.c
 * 
 * Copyright 2017 ss <ss@ss-system>
 * 
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
 * MA 02110-1301, USA.
 * 
 * 
 * use in linux terminal:
 *  
 * 1.	$ gcc -o source_00 source_00.c -lpthread
 * 2.	$ ./source_00 3
 * 3.	         ls
 * 		 time
 * 		 gcc -version
 */


/*
 * 
 * Include necessary library
 * 
 *
 * 
 */

#include <pthread.h>
#include <unistd.h>
#include <time.h>
#include <semaphore.h>
#include <stdio.h>
#include <stdlib.h>

#define NUM_THREADS 36
#define MAX 36

char matrix[6][6]; //result sheet

//queue elements
char queue[MAX], head=0, tail=0;


int row=0,col=0;
//track the number of times we have run the dispatch funciton
int runtime=1; 

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;


/*
 * 
 * name: dispatch
 * @param: void
 * @return: void
 * 
 */
void dispatch(void){
	row = runtime / 6;
	sleep(1); //wait 1 second to generate column number
	col = runtime % 6 - 1;
	if (runtime % 6 == 0)
	col = 5;
}

/*
 * 
 * name: enqueue
 * @param: character c   
 * @return: void
 * 
 */
void enqueue(char c){
	queue[tail] = c;
	tail = (tail+1)%MAX ;
}

/*
 * 
 * name: dequeue
 * @param: void
 * @return: character temp 
 * 
 */
char dequeue(){
	char temp = queue[head];
	head = (head+1)%MAX ;
	return temp;
}



/*
 * 
 * name: qcTask
 * @param: void * args   
 * @return: void
 * description: master thread
 */
void *qcTask(void *args)
{
	//simulate product convey delay
	sleep(1);
	pthread_mutex_lock(&mutex);
	dispatch();
	sleep(rand()%6+5);
	
	if(rand()%100<90){	
		enqueue('Q');
	}
	else{
		enqueue('U');
	}
	
	pthread_mutex_unlock(&mutex);

	pthread_exit(NULL);
}

/*
 * 
 * name: main
 * @param: int argc, char* argv[]
 * @return: int, no return value
 * description: program entry piont
 */
int main (int argc, char* argv[])
{
	//printf("This\n");
	
	if(argv[1] == NULL){
		printf("argv is NULL!\n");
	}
	printf("Enter some linux terminal command: \n");
	int input = atoi(argv[1]);/// converts string to integer
	//printf( "This\n");

	if(argc!=2 || input == 0 || input>36){
		printf("Input is illegal!\n");
	}
	else{
		pthread_t threads[input];
		//printf( "This\n");

		int rc, i, count = 0;

		srand(time(NULL));
		//printf( "This\n");
		for(i=0;i<input;i++){
			rc = pthread_create(&threads[i], NULL, qcTask, NULL);
			if (rc){
				printf("Error:unable to create thread%d\n",rc);	
				//cout << "Error:unable to create thread," << rc << endl;
				exit(-1);
			}
		}
		//printf( "This\n");
		for (i = 0; i < input; i++){
			//printf( "This p\n");
			rc = pthread_join(threads[i], NULL);
			
			if (rc){
			printf( "Error:unable to join,%d\n",rc);
			exit(-1);
			}
		}

		//initize matrix with default value 'i'
		//printf( "This\n");
		for (int i = 0; i < 6; i++){
			for (int j = 0; j < 6; j++){
				matrix[i][j] = 'I';
			}
		}
	
		//fill the result sheet
		for(int i=0;i<6;i++){
			for (int j = 0; j < 6; j++){
				matrix[i][j]=dequeue();
			}
		}

		for (int i = 0; i < 6; i++){
			for (int j = 0; j < 6; j++){
				printf( "%d",matrix[i][j]);
				if (matrix[i][j] == 'U'){
					count++;
				}
			}
			printf("\n");
		}

		printf("products are unqualified.\n");
		pthread_exit(NULL);
		}
		/// not reach to this piont
		printf( "End of Program Execution\n");
}

 * use in linux terminal:
 *  
 * 1.	$ gcc -o source_00 source_00.c -lpthread
 * 2.	$ ./source_00 3
 * 3.	ls
 *     time
 * 	gcc -version

ss@ss-system:~/Desktop/C_Programming/sw_dev$ ./source_00 3
Enter some linux terminal command: 
ls
dir
time
gcc --version
818181000
000000
000000
000000
000000
000000
products are unqualified.
ss@ss-system:~/Desktop/C_Programming/sw_dev$ ls
source_00  source_00.c
ss@ss-system:~/Desktop/C_Programming/sw_dev$ dir
source_00  source_00.c
ss@ss-system:~/Desktop/C_Programming/sw_dev$ time

real	0m0.000s
user	0m0.000s
sys	0m0.000s
ss@ss-system:~/Desktop/C_Programming/sw_dev$ gcc --version
gcc (Ubuntu 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE

[TheIdeasMan]

* use in linux terminal:
*
* 1. $ gcc -o source_00 source_00.c -lpthread

Set warnings to a high level:

gcc -std=c11 -Wall -Wextra -pedantic-errrors -o source_00 source_00.c -lpthread


In function 'void enqueue(char)':
86:12: warning: array subscript has type 'char' [-Wchar-subscripts]
In function 'char dequeue()':
98:24: warning: array subscript has type 'char' [-Wchar-subscripts]
At global scope: 112:20: warning: unused parameter 'args' [-Wunused-parameter]

Those warnings come about because of this line (53):

char queue[MAX], head=0, tail=0;

The way to avoid that warning is to always declare one variable per line:

char queue[MAX];
unsigned int head = 0;
unsigned int tail = 0;

The problem with char as a subscript is that it may be implemented as unsigned or signed char. So signed char is obviously a problem there.

I read somewhere (ISO CPP ?) that it is a good idea to compile C programs with a C++ compiler because they are better at handling types.

[eec]

Hi TheIdeasMan, thanks for improving my answer. can you please explain to me why compiling with c++ is better for type handling?

[TheIdeasMan]

eec wrote:

can you please explain to me why compiling with c++ is better for type handling?

Not sure exactly, IIRC they didn't say. Unfortunately I don't remember where I read that, so I probably should not have mentioned it.

Edit: I found it ...

https://isocpp.org/wiki/faq/mixing-c-and-cpp

BTW there is another way to handle this whole thing: compile all your code (even your C-style code) using a C++ compiler. That pretty much eliminates the need to mix C and C++, plus it will cause you to be more careful (and possibly —hopefully!— discover some bugs) in your C-style code. The down-side is that you’ll need to update your C-style code in certain ways, basically because the C++ compiler is more careful/picky than your C compiler. The point is that the effort required to clean up your C-style code may be less than the effort required to mix C and C++, and as a bonus you get cleaned up C-style code. Obviously you don’t have much of a choice if you’re not able to alter your C-style code (e.g., if it’s from a third-party).

The underlined part is here:
https://isocpp.org/wiki/faq/big-picture#back-compat-with-c

[eec]

thanks a lot, great answer.

[eec]

but accidentally you have a typo in

gcc -std=c11 -Wall -Wextra -pedantic-errrors -o source_00 source_00.c -lpthread

must be
gcc -std=c11 -Wall -Wextra -pedantic-errors -o source_00 source_00.c -lpthread

[eec]

for more information on Segmentation Faults read Good Alex Allain website

http://www.cprogramming.com/debugging/segfaults.html

[TheIdeasMan]

One thing to add to that article: In C++11 and later use nullptr, rather than NULL. nullptr was invented to fix the problems associated with using NULL with pointers.

[kbw]

Ending the program with pthread_exit(NULL); isn't right.

[benhart]

As a new I recommend taking some courses on the web as they can really useful and save you a lot of troubles. It's really important to know how to deal with errors and detect them quickly. If you're having troubles doing that on your own you can always use a program as help. I tend to use checkmarx and it works fine.
Good luck!
Ben.