I would like to create a custom policy derived from strict_real_policies that will parse reals, such as "3,14", i.e. with a comma decimal point as used e.g. in Germany.
That should be easy, right?
#include <iostream>
#include <string>
#include <boost/spirit/home/x3.hpp>
template <typename T>
struct decimal_comma_strict_real_policies:boost::spirit::x3::strict_real_policies<T>
{
template <typename Iterator>
static bool
parse_dot(Iterator& first, Iterator const& last)
{
if (first == last || *first != ',')
return false;
++first;
return true;
}
};
void parse(const std::string& input)
{
namespace x3=boost::spirit::x3;
std::cout << "Parsing '" << input << "'" << std::endl;
std::string::const_iterator iter=std::begin(input),end=std::end(input);
const auto parser = x3::real_parser<double, decimal_comma_strict_real_policies<double>>{};
double parsed_num;
bool result=x3::parse(iter,end,parser,parsed_num);
if(result && iter==end)
{
std::cout << "Parsed: " << parsed_num << std::endl;
}
else
{
std::cout << "Something failed." << std::endl;
}
}
int main()
{
parse("3,14");
parse("3.14");
}
Related
I tried to overload operator== for std::pair<int, int> so that only the first element of the pair would matter. Then, I'd like to use std::find to look for a particular element in std::vector<std::pair<int, int>>, using the overloaded operator==. But, it seems that, std::find is not using my overloaded operator==, though it is working in a simple comparison statement.
I expect the following code to output:
1
1
1
but I get:
1
1
0
Run on Linux, gcc 11.3:
#include <iostream>
#include <algorithm>
#include <vector>
#include <utility>
using namespace std;
typedef pair<int, int> p_int_t;
bool operator==(const p_int_t& p1, const p_int_t& p2)
{
return p1.first == p2.first;
}
int main()
{
vector<p_int_t> v;
v.push_back({1, 2});
v.push_back({1, 3});
p_int_t p(1, 4);
cout << (v[0] == p) << endl;
cout << (v[1] == p) << endl;
cout << (find(v.begin(), v.end(), p) != v.end()) << endl;
return 0;
}
The compiler does not select the free standing comparison operator because the type p_int_t is an alias, and it is not defined in the std namespace as std:: pair is. In other words, the compiler is looking for an operator with this signature: std::operator==(const std::pair<int, int>&, const std::pair<int, int>&); and finds it in algorithm.
You could declare your operator in the std namespace, which works, but is not recommended, or define p_int_t as a class, as in:
#include <algorithm>
#include <iostream>
#include <utility>
#include <vector>
using namespace std;
struct p_int_t : pair<int, int> {
using pair<int, int>::pair; // for c++=11 and later
p_int_t() : pair() {} // for c++98
p_int_t(int x, int y) : pair(x, y) {} // for c++98
friend bool operator==(const p_int_t& p1, const p_int_t& p2) {
return p1.first == p2.first;
}
};
int main() {
vector<p_int_t> v;
v.push_back({1, 2});
v.push_back({1, 3});
p_int_t p(1, 4);
cout << (v[0] == p) << endl;
cout << (v[1] == p) << endl;
cout << (find(v.begin(), v.end(), p) != v.end()) << endl;
return 0;
}
Code can be found here: https://godbolt.org/z/5dfPaaoMz
Having to redefine constructors is quite cumbersome, but you can also use std::find_if(), as in:
#include <algorithm>
#include <iostream>
#include <utility>
#include <vector>
using namespace std;
typedef pair<int, int> p_int_t;
struct compare_first {
p_int_t p;
compare_first(p_int_t x) : p(x) {}
bool operator()(const p_int_t& x) { return x.first == p.first; }
};
int main() {
vector<p_int_t> v;
v.push_back({1, 2});
v.push_back({1, 3});
p_int_t p(1, 4);
cout << (find_if(v.begin(), v.end(), compare_first(p)) != v.end()) << endl;
// or for c++11 or later...
cout << (find_if(v.begin(), v.end(), [&p](const p_int_t& x) { return p.first == x.first; }) != v.end()) << endl;
return 0;
}
Code here: https://godbolt.org/z/r87hdrrK9
I am trying to save the data the user inputted inside a linked-list and then store those data inside a file so that I can retrieve them back when I enter the 2nd option(as per in the int main()). Unfortunately, after I wrote the data into the file and check back the file, I found out that my data is missing and the file is filled with garbage.so I cant retrieve the data back. Is there any solution to this problem?? Thank you.
#include<iostream>
#include<cstdlib>
#include<iomanip>
#include<fstream>
using namespace std;
fstream fp;
class List{
private:
struct node{
string name;
string surname;
int idNum;
string nationality;
int number;
node *next;
}nod;
node* head;
node* curr;
node* temp;
public:
List();
bool isEmpty(node *head){
if(head==NULL){
return true;
}
else
return false;
}
void AddNode(string addName,string addsurName,int addId,string addNation,int addNumber);
void insertAsFirst(string addName,string addsurName,int addId,string addNation,int addNum);
//void DeleteNode(int delData);
void printList();
void write_linky(string name,string surName,int idNum,string nation,int number);
void read_linky();
}lb;
List::List(){
head=NULL;
curr=NULL;
temp=NULL;
}
void List::insertAsFirst(string addName,string addsurName,int addId, string addNation,int addNum){
node *n = new node;
n->name=addName;
n->surname=addsurName;
n->idNum=addId;
n->nationality=addNation;
n->number=addNum;
n->next = NULL;
head = n;
//last = temp;
}
void List::AddNode(string addName,string addsurName,int addId,string addNation,int addNum){
if(isEmpty(head)){
insertAsFirst(addName,addsurName,addId,addNation,addNum);
}
else{
node* n = new node;
n->next=NULL;
n->name=addName;
n->surname=addsurName;
n->idNum=addId;
n->nationality=addNation;
n->number=addNum;
curr = head;
while(curr->next != NULL){
curr = curr->next;
}
curr->next = n;
}
}
void List::printList(){
curr=head;
cout << "\n\t\t\t\t CUSTOMER INFO" << endl << endl;
cout <<"NAME" << setw(20) << "SURNAME" << setw(20) << "ID NO. " << setw(20) << "NATIONALLITY" << setw(20) << "TELEPHONE" << endl << endl;
while(curr != NULL){
cout << curr -> name << setw(20) << curr -> surname << setw(20) << curr -> idNum << setw(20) << curr -> nationality << setw(20) << curr -> number << endl << endl;
curr=curr->next;
/*cout<<curr->number << endl;
cout<<curr->age << endl;
cout<<curr->idNum << endl;
cout<<curr->name<< endl;
cout<<curr->surname << endl;
cout<<curr->nationality << endl;
curr = curr->next;
}
*/
}
}
void List::write_linky(string name,string surName,int idNum,string nation,int number)
{
fp.open("Link.dat",ios::out|ios::app);
lb.AddNode(name,surName,idNum,nation,number);
lb.printList();
fp.write((char*)&nod,sizeof(node));
fp.close();
cout<<"\n\nThe Data Has Been Added ";
}
void List::read_linky(){
fp.open("Link.dat",ios::in);
while(fp.read((char*)&nod,sizeof(node)))
{
lb.printList();
//cout<<"\n\n=====================================================\n";
//getch();
}
fp.close();
//getch();
}
int main(){
List lb;
int idNum,number;
string name,surname,nationality;
char choice,ch;
cout<<"Please select your choice"<<endl;
cout<<"1.Book ticket"<<endl;
cout<<"2.view details"<<endl;
cin>>ch;
switch(ch){
case '1':
do{
cout<< "Enter name: ";
cin>>name;
cout<< "Enter surname: ";
cin>>surname;
cout<< "Enter identification number: ";
cin>>idNum;
cout<< "Enter your nationality: ";
cin>>nationality;
cout<< "Enter contact number: ";
cin>>number;
lb.write_linky(name,surname,idNum,nationality,number);
//lb.AddNode(number,age,idNum,name,surname,nationality);
cout<<"\n\nDo you want to add more entry?";
cin>>choice;
}while(choice=='y');
break;
case '2':
lb.read_linky();
break;
}
}
//lb.printList();
I've never done this but I'd guess string is a complex structure that doesn't lend itself to being written to disk like this. As a test change these to (say) char[255] and it might be happier.
None of the standard library containers will call delete on contained raw pointers. I have checked for a solution on SO for C++98 but have not found the answer.
I have created template <typename K, typename V> void clearAndDestroy( std::map<K, V*> *&myMap) as a replacement function for std::clear() (remove all elements and call the destructors).
It works for maps with pointers to objects std::map(key,V*). The function works also for cases when map contains same V* pointers for the different keys.
#include <iostream>
#include <map>
#include <string>
#include <set>
using namespace std;
// clearAndDestroy deletes all objects and remove them from the std::map(K,V*) container.
template <typename K, typename V>
void clearAndDestroy( std::map<K, V*> *&myMap)
{
if(myMap == NULL)
return;
std::set<V*> mySet;
typename std::map<K,V*>::iterator itr;
typename std::set<V*>::iterator sitr;
itr = myMap->begin();
while (itr != myMap->end()) {
mySet.insert(itr->second);
++itr;
}
sitr = mySet.begin();
while (sitr != mySet.end()) {
delete(*sitr);
++sitr;
}
myMap->clear();
}
template <typename K, typename V> void clear1( std::map<K, V*> *myMap)
{
if(myMap == NULL) return;
typename std::map<K, V*>::iterator itr = myMap->begin();
while (itr != myMap->end()) {
typename std::map<K, V*>::iterator toErase = itr;
++itr;
myMap->erase(toErase);
delete(toErase->second);
}
}
template <typename M> void clear2( M *myMap )
{
if(myMap == NULL) return;
for ( typename M::iterator it = myMap->begin(); it != myMap->end(); ++it ) {
delete it->second;
}
myMap->clear();
}
class MY_CLASS
{
public:
int counter;
string *message;
MY_CLASS(int c, string *m):counter(c), message(m) {
std::cout << "Constructor MY_CLASS " << this << std::endl;
};
~MY_CLASS()
{
if(message) {
cout << "Being destroyed MY_CLASS: " << *message << " this = " << this <<endl;
}
else {
cout << "Being destoyed MY_CLASS: " << " this = " << this <<endl;
}
if(message) {
delete message;
message = NULL;
}
}
MY_CLASS(const MY_CLASS & other)
{
std::cout << "Copy Constructor MY_CLASS " << this << std::endl;
//1.
counter = other.counter;
//2.
if(other.message) {
message = new string;
*message = *other.message; // copy the value
}
else {
message = NULL;
}
}
};
void print(const string *str,MY_CLASS *& value, void *)
{
if (value && value->message)
cout << value->counter << " ! " << *(value->message) << endl;
}
int main() {
std::map<std::string, MY_CLASS *> *mpa = new std::map<std::string, MY_CLASS *>;
MY_CLASS *p = new MY_CLASS(2, new string("abc"));
mpa->insert(std::pair<std::string, MY_CLASS *>("1", p));
mpa->insert(std::pair<std::string, MY_CLASS *>("2", p));
clearAndDestroy(mpa);
delete mpa;
return 0;
}
Output:
Constructor MY_CLASS 0x111ccb0
Being destroyed MY_CLASS: abc this = 0x111ccb0
Being restricted to C++98 is clearAndDestroy my best option? Thank you!
Another approach you can take is using an object wrapper. Place the pointer you want within an object and have the destructor call the delete on the pointer. Basically building a simple "smart-pointer".
class AutoDeletePtr {
MY_CLASS* pointer;
AutoDeletePtr(MY_CLASS* myObjectPtr) {pointer = myObjectPtr};
~AutoDeletePtr() {delete(pointer)};
}
You can insert these objects into the std::map.
I'm not able to make this code work using fellowed convention of header includes.
help.cpp
#include <iostream>
#include "basicMath.h"
using namespace std;
int main() {
int arr[4]={0,1,2,3};
int k=0;
int m=3;
//permutations call
perm(arr,k,m);
return 0;
}
BasicMath.h
#ifndef BASICMATH_H_
#define BASICMATH_H_
template<class T>
void Swap ( T& a, T& b );
template<class T1>
void perm ( T1 arr[], int k, int m);
#endif /* BASICMATH_H_ */
BasicMath.cpp
#include <iostream>
#include "basicMath.h"
using namespace std;
template<class T>
void Swap ( T& a, T& b )
{
T temp;
b=temp;
b=a;
a=temp;
}
template<class T1>
void perm ( T1 arr[], int k, int m)
{
//base case
cout << "Call: " << arr[0] << arr[1] << arr[2] << arr[3] << "\t" << k << "\t" << m << "\n";
if (k==m) {
for (int i=0;i<=m;i++) {
cout << arr[i];
}
cout << endl;
} else {
for (int i=k;i<=m;i++) {
swap(arr[k],arr[i]);
perm(arr,k+1,m);
swap(arr[k],arr[i]);
}
}
}
IF I replace the #include "basicMath.h" by #include "basicMath.cpp" Then program works.
Please help. New to Eclipse Project using headers and src.
Thanks in Adv.
The "simple" answer is that you can't put the implementation of a template function into a .cpp file.
See http://www.parashift.com/c++-faq/templates-defn-vs-decl.html
I struggled with the following code. My signal handler on_button_press_event() is never called but I have no idea why. Could someone have a look on it? Maybe someone is able to run through the gtkmm lib with debug infos. I only have the pre-installed gtkmm packages which could not be used for debugging into the library itself.
#include <iostream>
using namespace std;
#include <gtkmm.h>
#include <goocanvasmm.h>
bool MyExternalHandler( const Glib::RefPtr<Goocanvas::Item>& item, GdkEventButton* ev )
{
cout << "External Handler" << endl;
return false;
}
class MyRect : public Goocanvas::Rect
{
public:
MyRect( double x, double y, double w, double h)
//: Goocanvas::Rect( x,y,w,h)
{
property_x()=x;
property_y()=y;
property_width()=w;
property_height()=h;
}
public:
virtual void nonsens() {}
bool on_button_press_event(const Glib::RefPtr<Item>& target, GdkEventButton* event) override
{
cout << "override handler" << endl;
return false;
}
bool Handler( const Glib::RefPtr<Goocanvas::Item>& item, GdkEventButton* ev )
{
cout << "via mem_fun" << endl;
return false;
}
bool on_enter_notify_event(const Glib::RefPtr<Item>& target, GdkEventCrossing* event) override
{
cout << "override enter notify" << endl;
return false;
}
};
int main(int argc, char* argv[])
{
Gtk::Main app(&argc, &argv);
Goocanvas::init("example", "0.1", argc, argv);
Gtk::Window win;
Goocanvas::Canvas m_canvas;
m_canvas.set_size_request(640, 480);
m_canvas.set_bounds(0, 0, 1000, 1000);
MyRect* ptr;
Glib::RefPtr<MyRect> m_rect_own(ptr=new MyRect(225, 225, 150, 150));
m_rect_own->property_line_width() = 1.0;
m_rect_own->property_stroke_color() = "black";
m_rect_own->property_fill_color_rgba() = 0x555555ff;
Glib::RefPtr<Goocanvas::Item> root = m_canvas.get_root_item();
root->add_child( m_rect_own);
((Glib::RefPtr<Goocanvas::Item>&)m_rect_own)->signal_button_press_event().connect(sigc::ptr_fun(&MyExternalHandler));
((Glib::RefPtr<Goocanvas::Item>&)m_rect_own)->signal_button_press_event().connect(sigc::mem_fun(*ptr, &MyRect::Handler));
win.add(m_canvas);
win.show_all_children();
Gtk::Main::run(win);
return 0;
}
Your on_button_press_event() method is not an override, because it has the wrong parameters:
https://developer.gnome.org/gtkmm/unstable/classGtk_1_1Widget.html#aba72b7f8655d1a0eb1273a26894584e3