example.c

/*=============================================================================
# Filename: example.c
# Author: bookug
# Mail: bookug@qq.com
# Last Modified: 2018-10-09 08:13
# Description: union two sorted lists, and apply the sqrt operator on each item
# For debug, gcc -std=c99 -g inc/list.c example.c -o run.exe -lm
# To release, gcc -std=c99 -O2 inc/list.c example.c -o run.exe -lm
=============================================================================*/

#include <stdio.h>
#include <math.h> 
#include <stdlib.h> 
#include <limits.h> 
//Another choice is to use 'inc/list.h' here
#include "list.h"

//A safe way to release memory
#define xfree(p) free(p);p=NULL;

#define list1_num 1000
#define list2_num 1000

//this is placed in .data segment, and it can be assigned larger space than function stack(1M by default). For larger space, use heap memory instead
int list1[list1_num];
int list2[list2_num];

/**
 * @author bookug
 * @function prepare the data for two lists
 * @param no parameters needed
 * @return no value returned here
 */
void produceData()
{
    for(int i = 0; i < list1_num; ++i)
    {
        list1[i] = 2 * i + 1;
    }

    for(int i = 0; i < list2_num; ++i)
    {
        list2[i] = 2 * (i+1);
    }
}

/**
 * @author bookug
 * @function the main function of C program
 * @param number of arguments in the command, including the program itself
 * @param all argument strings
 * @return no value returned here
 */
int main(int argc, const char* argv[])
{
    produceData();
    //NOTICE: if liblist.so is not found by system, then the program will stop at once, which means the code below will not be run and output
    //(this indicates that the program will not run until the first call of functions of liblist.so)
    //We can use 'strace ./run.exe' command to see details, operating system will search and open all dynamic libraries first!
    //(this is different from dlopen)
    printf("check before dynamic\n");

    Node *result_head = NULL, *result_tail = NULL;
    int pos1 = 0, pos2 = 0;
    //NOTICE: this strategy not always fails, for example, the final elements of the two lists are the same
    while(pos1 < list1_num || pos2 < list2_num)
    //while(pos1 < list1_num && pos2 < list2_num)
    {
        /*printf("check %d %d\n", pos1, pos2);*/
        if(list1[pos1] < list2[pos2])
        {
            addResult(&result_head, &result_tail, list1[pos1]);
            pos1++;
        }
        else if(list1[pos1] > list2[pos2])
        {
            addResult(&result_head, &result_tail, list2[pos2]);
            pos2++;
        }
        else   //equal case, only add once
        {
            addResult(&result_head, &result_tail, list1[pos1]);
            pos1++;
            pos2++;
        }
    }

//    while(pos1 < list1_num)
//    {
//        addResult(&result_head, &result_tail, list1[pos1]);
//        pos1++;
//    }
//    while(pos2 < list2_num)
//    {
//        addResult(&result_head, &result_tail, list2[pos2]);
//        pos2++;
//    }

    //NOTICE: the declaration Node* p=... in for-loop is only allowed in C99 standard
    //output each item in result after sqrt operation
    for(Node* p = result_head; p != NULL; p = p->next)
    {
        //NOTICE: sqrt(8) works but sqrt(n) must be compiled by -lm
        double r = sqrt((double)(p->val));
        printf("%lf\n", r);
    }

    //NOTICE: another bug exists here, but error is not reported when running
	//This is because system will only report error if this region is already used by another program(or the kernel)
	//Otherwise system will not spend time on clearing its content, so you can still access it as before
	//However, theorectically it has been freed and access is invalid, may cause unsure risks
	//(it may runs correctly, and gdb can not find the error, but valgrind can, so you are advised to use valgrind to check all possible memory invalid operations before you publish your software)
    //printf("%p %p\n", result_head, result_tail);
    //release the result list
    for(Node* p = result_head; p != NULL; p = p->next)
    {
        free(p);
        //NOTICE: this set will cause segment fault immediately
        //p = NULL;
        //printf("%p\n", p);
    }
    //clear the list pointers, head and tail
    result_head = result_tail = NULL;

    return 0;
}