Segment fault! Need help

[pnthoai123]

I receive the Segment fault (core dumped) error when I build the small queue by using pointer below.

#include <stdio.h>
#include <stdlib.h>

struct data {
	int pid;
	struct data *next;
};
struct data1 {
	struct data *head;
	struct data *tail;
};

void initial_data(struct data * tes){
	tes->pid = 5;
	tes->next = NULL;
}
int empty(struct data1 *q){
	return (q->head == NULL);
}
struct data * de_queue(struct data1 * q) {
	struct data * proc;
	if(empty(q)){
		proc = NULL;
	}
	else {
		proc = q->head;
		q->head = q->head->next;
	}
	// YOUR CODE HERE

	return proc;
}

void en_queue(struct data1 * q, struct data * proc) {
	printf("%d\n", proc->pid); // here it prints
	if(empty(q)){
		printf("%d\n", proc->pid); 	// from here it does not print
		q->head = proc;
		q->tail = proc;
	}
	else {
		q->tail->next = proc;
		q->tail = q->tail->next;
	}	
}
int main(){
	struct data1 queue;
	struct data tes;
	initial_data(&tes);
	en_queue(&queue, &tes);
}

[coder777]

You never set head or tail to null, hence empty(...) will probably never return 1 and the data is inserted at an invalid position.

[MikeyBoy]

Use your debugger to step through the program. You'll be able to see exactly where it's crashing, and to examine the contents of the memory to see why it's crashing.

HINT: What value q->head to have at line 36?

[pnthoai123]

thank both you! I did not recognize those

[MikeyBoy]

You're welcome!

Although my advice still stands: learn to use your debugger, so that you can investigate and fix these kinds of bugs yourself.