I'm newer to C++. I have written some code, but when i run it, there's always this:
raised exception class
EAccessViolation with message 'Access
violation at address'
i don't understand this. Would you like to help me solve it? It's important to me. Really, really thank you!
#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <math.h>
#include <conio.h>
#define k 2
#define minoffset 0.5
using namespace std;
struct Point
{
double X;
double Y;
};
vector<Point> dataprocess();
void k_means(vector<Point> points,int N);
double getdistance(Point p1,Point p2)
{ double distance;
distance=sqrt((p1.X-p2.X)*(p1.X-p2.X)+(p1.Y-p2.Y)*(p1.Y-p2.Y));
return distance;
}
int getmindis(Point p,Point means[])
{
int i;
int c;
double dis=getdistance(p,means[0]);
for(i=1;i<k;i++)
{
double term=getdistance(p,means[i]);
if(term<dis)
{
c=i;
dis=term;
}
}
return c;
}
Point getmeans(vector<Point> points)
{
int i;
double sumX,sumY;
Point p;
int M=points.size();
for(i=0;i<M;i++)
{
sumX=points[i].X;
sumY=points[i].Y;
}
p.X=sumX/M;
p.Y=sumY/M;
return p;
}
int main()
{ int N;
vector<Point> stars;
stars=dataprocess();
N=stars.size();
cout<<"the size is:"<<N<<endl;
k_means(stars,N);
getch();
}
vector<Point> dataprocess()
{
int i;
int N;
double x,y;
vector<Point> points;
Point p;
string import_file;
cout<<"input the filename:"<<endl;
cin>>import_file;
ifstream infile(import_file.c_str());
if(!infile)
{
cout<<"read error!"<<endl;
}
else
{
while(infile>>x>>y)
{
p.X=x;
p.Y=y;
points.push_back(p);
}
}
N=points.size();
cout<<"output the file data:"<<endl;
for(i=0;i<N;i++)
{
cout<<"the point"<<i+1<<"is:X="<<points[i].X<<" Y="<<points[i].Y<<endl;
}
return points;
}
void k_means(vector<Point> points,int N)
{
int i;
int j;
int index;
vector<Point> clusters[k];
Point means[k];
Point newmeans[k];
double d,offset=0;
bool flag=1;
cout<<"there will be"<<k<<"clusters,input the original means:"<<endl;
for(i=0;i<k;i++)
{
cout<<"k"<<i+1<<":"<<endl;
cin>>means[i].X>>means[i].Y;
}
while(flag)
{
for(i=0;i<N;i++)
{
index=getmindis(points[i],means);
clusters[index].push_back(points[i]);
}
for(j=0;j<k;j++)
{
newmeans[j]=getmeans(clusters[j]);
offset=getdistance(newmeans[j],means[j]);
}
if(offset>d)
{
d=offset;
}
flag=(minoffset<d)?true:false;
for(i=0;i<k;i++)
{
means[i]=newmeans[i];
clusters[i].clear();
}
}
for(i=0;i<k;i++)
{
cout<<"N"<<i+1<<"="<<clusters[i].size()<<endl;
cout<<"the center of k"<<i+1<<"is:"<<means[i].X<<" "<<means[i].Y<< endl;
}
}
You surely have some algo errors in you code. It is difficult to deal with code without input data, that caused an error, but let's try:
First, lets look at function Point getmeans(vector<Point> points)
it is supposed to evaluate mean coordinates for cluster of points: if you pass an empty cluster to this function it will cause an error:
look here -
int M=points.size()
and here -
for(i=0;i<M;i++)
{
sumX=points[i].X;
sumY=points[i].Y;
}
if your cluster is empty than M will be zero and you loop will iterate 2^31 times (until 32 bit integer overflow) and each time you will try to read values of nonexistent vector items
So, You have to test if you vector is not empty before running main function loop and you have to decide which mean values should be assigned for zero cluster (May be you need an additional flag for empty cluster which will be checked before dealing with cluster's mean values)
Then lets examine function int getmindis(Point p,Point means[]) and, also, a place, where we call it:
index=getmindis(points[i],means); clusters[index].push_back(points[i]);
This function assings points to clusters. cluster number is ruled by c variable. If input point doesn't fit to any cluster, function will return uninitialized variable (holding any possible value) which. then is used as vector index of nonexisting element - possible access violation error
You probably have to initialize c to zero in declaration
Tell us when you will be ready with errors described above and also show us a sample input file (one which causes errors, if all datasets cause errors, show us the smallest one)
Related
// Online C++ compiler to run C++ program online
#include <bits/stdc++.h>
using namespace std;
struct Node{
int data;
Node *next;
Node(int val)
{
data=val;
next=NULL;
}
};
Node* findIntersection(Node* head1, Node* head2)
{
// Your Code Here
Node* h=nullptr;
Node* temp=h;
while(head2!=nullptr){
while(head1!=nullptr && head1->data<head2->data){
head1=head1->next;
}
cout<<head1->data<<endl;
if(head1->data==head2->data){
if(h==nullptr){
h=new Node(head1->data);
}
else{
temp->next=new Node(head1->data);
temp=temp->next;
}
}
head2=head2->next;
}
return h;
}
int main() {
// Write C++ code here
Node* l1= new Node(1);
l1->next=new Node(2);
l1->next->next=new Node(3);
l1->next->next->next=new Node(4);
l1->next->next->next->next=new Node(6);
Node* l2=new Node(2);
l1->next=new Node(4);
l1->next->next=new Node(6);
l1->next->next->next=new Node(8);
findIntersection(l1,l2);
return 0;
}
I tried to find intersection of two linked lists with elements in sorted order.
This is a question on GFG which can be found on link:
https://practice.geeksforgeeks.org/problems/intersection-of-two-sorted-linked-lists/1?page=1&category[]=Linked%20List&sortBy=difficulty
Why this code is giving segmentation fault in linked list intersection?
Because there are bugs in it. You'll benefit from learning how to debug small programs.
#include <bits/stdc++.h>
Unrelated to your crash, but you should never #include anything from the bits directory.
while(head2!=nullptr){
while(head1!=nullptr && head1->data<head2->data){
head1=head1->next;
}
// We could get here if head1==nullptr. The next line will crash.
cout<<head1->data<<endl;
...
else {
// temp was assigned NULL in the start, and now is being dereferenced.
temp->next=new Node(head1->data);
temp=temp->next;
}
You can write the prototypes without the variable names?
int example(examplestruct *var1, examplestruct *var2);
void done(examplestruct *var1,FILE *f);
struct {
int* field1;
int field2;
}examplestruct;
Is it possible to write the prototypes without name variables?
Can anyone tell me if this is acceptable in C language? You can write the prototypes without the variable names?
Yes.
As for the second question:
If you want a function to be inside main(), then take the body of the function, put it in main() and make sure that the arguments that the function had are well handled.
This example will clear things up:
#include <stdio.h>
void print(int);
void inc_p(int);
int main(void) {
int num = 5;
print(num);
inc_p(num);
// to get rid of inc_p(), copy paste it's body inside main
// and you will get this
// a++;
// print(a);
// However, a was an argument, here you need to use
// the variable declared in main(), i.e. 'num'
num++;
print(num);
return 0;
}
void print(int a) {
printf("%d\n", a);
}
void inc_p(int a) {
a++;
print(a);
}
Consider the following code which prints out the even numbers up to 20:
import std.stdio;
class count_to_ten{
static int opApply()(int delegate(ref int) dg) {
int i = 1;
int ret;
while(i <= 10){
ret = dg(i);
if(ret != 0) {
break;
}
i++;
}
return ret;
}
}
void main() {
int y = 2;
foreach(int x; count_to_ten) {
writeln(x * y);
}
}
The syntax of opApply requires that it take a delegate or function as a normal argument. However, even if we relaxed that and allowed opApply to take a function as a template argument, we still would have no recourse for delegates because D doesn't provide any way to separate the stack-frame pointer from the function pointer. However, this seems like it should be possible since the function-pointer part of the delegate is commonly a compile-time constant. And if we could do that and the body of the loop was short, then it could actually be inlined which might speed this code up quite a bit.
Is there any way to do this? Does the D compiler have some trick by which it happens automagically?
I'm trying Lua and want to know how lua_State working
code and result:
state.c
#include <stdio.h>
#include "lua/src/lua.h"
#include "lua/src/lauxlib.h"
static void stackDump(lua_State *L){
int i;
int top = lua_gettop(L);
for(i = 1; i<= top; i++) {
int t = lua_type(L, i);
switch(t){
case LUA_TSTRING:
printf("'%s'", lua_tostring(L, i));
break;
case LUA_TBOOLEAN:
printf(lua_toboolean(L, i) ?"true":"false");
break;
case LUA_TNUMBER:
printf("%g", lua_tonumber(L, i));
break;
default:
printf("%s", lua_typename(L, t));
break;
}
printf(" ");
}
printf("\n");
}
static int divide(struct lua_State *L){
double a = lua_tonumber(L, 1);
double b = lua_tonumber(L, 2);
printf("%p\n", L);
stackDump(L);
int quot = (int)a / (int)b;
int rem = (int)a % (int)b;
lua_pushnumber(L, quot);
lua_pushnumber(L, rem);
stackDump(L);
printf("---end div---\n");
return 2;
}
int main(void){
struct lua_State *L = lua_open();
lua_pushboolean(L, 1);
lua_pushnumber(L, 10);
lua_pushnil(L);
lua_pushstring(L, "hello");
printf("%p\n", L);
stackDump(L);
lua_register(L, "div", divide);
luaL_dofile(L, "div.lua");
stackDump(L);
lua_close(L);
return 0;
}
div.lua
local c = div(20, 10)
0x100c009e0
true 10 nil 'hello'
---start div---
0x100c009e0
20 10
20 10 2 0
---end div---
true 10 nil 'hello'
I see lua_State in divide is the same with the main one, but they have different data in stack, How this be done ?
I know the best way to understand this is to read source code of Lua , maybe you can tell me where to find the right place.
Think of lua_State as containing the Lua stack, as well as indices delimiting the current visible part of the stack. When you invoke a Lua function, it may look like you have a new stack, but really only the indices have changed. That's the simplified version.
lua_State is defined in lstate.h. I've pulled out the relevant parts for you. stack is the beginning of the big Lua stack containing everything. base is the beginning of the stack for the current function. This is what your function sees as "the stack" when it is executing.
struct lua_State {
/* ... */
StkId top; /* first free slot in the stack */
StkId base; /* base of current function */
/* ... */
StkId stack_last; /* last free slot in the stack */
StkId stack; /* stack base */
/* ... */
};
Programming in Lua, 2nd Edition discusses Lua states in chapter 30: Threads and States. You'll find some good information there. For example, lua_State not only represents a Lua state, but also a thread within that state. Furthermore, all threads have their own stack.
It gets different data the same way anything gets different data: code changes the data inside of the object.
struct Object
{
int val;
};
void more_stuff(Object *the_data)
{
//the_data->val has 5 in it now.
}
void do_stuff(Object *the_data)
{
int old_val = the_data->val;
the_data->val = 5;
more_stuff(the_data);
the_data->val = old_val;
}
int main()
{
Object my_data;
my_data.val = 1;
//my_data.val has 1.
do_stuff(&my_data);
//my_data.val still has 1.
}
When Lua calls a registered C function, it gives it a new stack frame.
For a user-lever thread library, I need to figure out jumping to a function by modifying PC value stored in jmp_buf.
This is what I have written:
jmp_buf env;
void print (void) {
printf("\nHello World!");
}
static int ptr_mangle(int p) {
unsigned int ret;
asm(" movl %1, %%eax;\n"
" xorl %%gs:0x18, %%eax;"
" roll $0x9, %%eax;"
" movl %%eax, %0;"
: "=r"(ret)
: "r"(p)
: "%eax"
);
return ret;
}
int main() {
int i = setjmp(env);
env[0].__jmpbuf[5] = ptr_mangle(print);
longjmp(env, 2);
return 0;
}
I am trying to modify PC in jmp_buf by setting it to the address of the function I am trying to jump to.
I am getting a segmentation fault.
I am unable to figure out what exactly needs to be done. Do I need to modify SP as well?
Any help would be very much appreciated.
What are you trying to do? Are you not checking for the return value of setjmp? I don't think you are doing this correctly. Have a look at the sample code below to see what would be the output be:
#include <stdio.h>
#include <setjmp.h>
#include <stdlib.h>
void subroutine(jmp_buf);
int main(void)
{
int value;
jmp_buf jumper;
value = setjmp(jumper);
if (value != 0)
{
printf("Longjmp with value %d\n", value);
exit(value);
}
printf("About to call subroutine ... \n");
subroutine(jumper);
return 0;
}
void subroutine(jmp_buf jumper)
{
longjmp(jumper,1);
}
The output would be:
About to call subroutine...
Longjmp with a value of 1.
Which begs the question - why are you trying to modify the IP? It sounds like you overwrote something or the code 'jumped' off into the woods and trampled something and came back with a hard landing i.e. segfault.
The variable env is specifically a struct, do not use an array subscript as you have done. I suspect that is why you got a segfault...
Hope this helps,
Best regards,
Tom.