I am currently working on a bit of code that will search within a vector of type Person (which I have defined in the code and will show if needed). If it finds the person, it returns their name. This is currently working, but if it does not find the person, it is supposed to return a Null pointer. The problem is, I cannot figure out how to make it return a Null pointer! It just keeps either crashing the program every time.
Code:
Person* lookForName(vector<Person*> names, string input)
{
string searchName = input;
string foundName;
for (int i = 0; i < names.size(); i++) {
Person* p = names[i];
if (p->getName() == input) {
p->getName();
return p; //This works fine. No problems here
break;
} else {
//Not working Person* p = NULL; <---Here is where the error is happening
return p;
}
}
}
You could use std::find_if algorithm:
Person * lookForName(vector<Person*> &names, const std::string& input)
{
auto it = std::find_if(names.begin(), names.end(),
[&input](Person* p){ return p->getName() == input; });
return it != names.end() ? *it : nullptr; // if iterator reaches names.end(), it's not found
}
For C++03 version:
struct isSameName
{
explicit isSameName(const std::string& name)
: name_(name)
{
}
bool operator()(Person* p)
{
return p->getName() == name_;
}
std::string name_;
};
Person * lookForName(vector<Person*> &names, const std::string& input)
{
vector<Person*>::iterator it = std::find_if(names.begin(), names.end(),
isSameName(input));
return it != names.end() ? *it : NULL;
}
If the name you are searching for is not at the first element, then you are not searching in the rest of the elements.
You need to do something like -
for (int i = 0; i<names.size(); i++){
Person* p = names[i];
if (p->getName() == input) {
return p;
// Placing break statement here has no meaning as it won't be executed.
}
}
// Flow reaches here if the name is not found in the vector. So, just return NULL
return NULL;
As Chris suggested, try using std::find_if algorithm.
Looks like you just have to return Null, nullptr, or 0.
codeproject
Just use following code:
return NULL;
Related
Requirements for this function: If the full name (both the first and last name) is not equal to any full name currently in the list then add it and return true. Elements should be added according to their last name. Elements with the same last name should be added according to
their first names. Otherwise, make no change to the list and return false (indicating that the name is already in the list).
//this function add nodes to the list
//return true if fullname isn't in the list. Else return false if fullname is in the list.
//should be added according to last name.
bool OnlineDating::makeMatch(const std::string& firstName, const std::string& lastName, const OnlineType& value)
{
Node* p = head;
//are these nodes already set to firstName and lastName in this function
Node first;
Node last;
Node* temp = nullptr;
//if the list is empty just insert the fullname and value to the list
if (p == nullptr) {
//add values to the empty list
insertToRear(firstName, lastName, value);
return true;
}
else {
// so this loop is to check if fullname is in the list but first sort in alphebetial order
//sure its added in alphebetical order
//traverse the list after knowing where head is
while (p != nullptr) {
//checking to make sure theres at least another node in the list
if (p->next != nullptr) {
//its not going through ig loop?
//these are used to check and alphebetically selected names
if (p->last > p->next->last) {
insertToRear(p->first, p->last, p->value);
p->next = temp;
return true;
}
else if (p->next->last > p->last) {
insertToRear(p->first, p->last, p->value);
p->next = temp;
return true;
}
//check if full name is already in the list
if (p->last == p->next->last) {
insertToRear(p->first, p->last, p->value);
p->next = temp;
return true;
}
else if (p->first > p->next->first) {
insertToRear(p->first, p->last, p->value);
p->next = temp;
return true;
}
else {
//returns false if it passes through these checks
return false;
}
}
p = p->next;
}
}
}
Here is my main.cpp
int main()
{
OnlineDating clippersGonnaClip;
clippersGonnaClip.makeMatch("Kawhi", "Leonard", 2);
clippersGonnaClip.makeMatch("Paul", "George", 13);
clippersGonnaClip.makeMatch("Ivica", "Zubac", 40);
clippersGonnaClip.makeMatch("Reggie", "Jackson", 1);
clippersGonnaClip.makeMatch("Patrick", "Beverley", 21);
for (int n = 0; n < clippersGonnaClip.howManyMatches(); n++) {
string first;
string last;
int val;
clippersGonnaClip.confirmMatch(n, first, last, val);
cout << first << " " << last << " " << val << endl;
}
return 0;
}
honestly, I just want to create a ptr that will point to each node. Check as long as that node isn't pointing to nullptr, and sort the LinkedList in alphabetical order. finally link the nodes together using my *temp. Why won't it let me go through the if statements every time I compile I get a negative number? Every other function works for this program except this makeMatch(...).
Nothing in the requirements says anything about the data types you need to use. In this case using std::set makes most sense.
By providing a comparison operation on persons and a set you can guarantee uniqueness. Like this :
#include <set>
#include <string>
struct person_t
{
std::string name;
std::string last_name;
unsigned int age;
};
bool operator<(const person_t& lhs, const person_t& rhs)
{
if (lhs.last_name == rhs.last_name)
return lhs.name < rhs.name;
return lhs.last_name < rhs.last_name;
}
int main()
{
// set will ensure all persons are unique
std::set<person_t> persons;
persons.insert({ "Kawhi", "Leonard", 2 });
persons.insert({ "Paul", "George", 13 });
persons.insert({ "Ivica", "Zubac", 40 });
persons.insert({ "Reggie", "Jackson", 1 });
persons.insert({ "Patrick", "Beverley", 21 });
}
So I'm trying to print a string, but I get no output. However the other values in the class prints just fine.
In main I have a for loop that prints the the values for the Skill class. In Skill I have a pointer to the Ability class.
class Skill {
private:
Ability* ability;
public:
Ability* GetAbility() {
return ability;
};
}
It gets assigned in the constructor like this:
Skill::Skill(Ability* ability){
this->ability = ability;
}
The Ability class contains just a Name and a score.
class Ability {
private:
string name;
float score;
public:
Ability(string name, float score) {
this->name = name;
this->score = score;
};
string Name() { return name; }
float GetScore() { return score; }
};
Now in main I create a few skills and assign an ability to it. as is a container class that initializes a few ablities in a vector and I can get an ability based on its name.
Skill s* = new Skill[2]
s[0] = Skill(&as.GetAbility("Strength"));
s[1] = Skill(&as.GetAbility("Charisma"));
And then we print
cout << s[i].GetAbility()->Name() << " " << s[i].GetAbility()->GetScore();
However the only output I get is the score. No name what so ever and I can't figure it out. I've tried a few things, but still noting is printing. I'm sure I'm missing something simple that will make me facepalm, but in my defense I haven't written C++ in over 10 years. Thanks in advance.
EDIT: as.GetAbility looks like this:
Ability AbilityScores::GetAbility(string abilityName) {
for (int i = 0; i < abilityScores.size(); i++) {
if (abilityScores[i].Name() == abilityName) {
return abilityScores[i];
}
}
return Ability();
}
abilityScores is a vector
Your AbilityScores::GetAbility() method is returning an Ability object by value, which means it returns a copy of the source Ability, and so your Skill objects will end up holding dangling pointers to temporary Ability objects that have been destroyed immediately after the Skill constructor exits. So your code has undefined behavior.
AbilityScores::GetAbility() needs to return the Ability object by reference instead:
Ability& AbilityScores::GetAbility(string abilityName) {
for (int i = 0; i < abilityScores.size(); i++) {
if (abilityScores[i].Name() == abilityName) {
return abilityScores[i];
}
}
throw ...; // there is nothing to return!
}
...
Skill s* = new Skill[2];
s[0] = Skill(&as.GetAbility("Strength"));
s[1] = Skill(&as.GetAbility("Charisma"));
...
If you want to return a default Ability when the abilityName is not found, consider using std::map instead of std::vector:
private:
std::map<std::string, Ability> abilityScores;
AbilityScores::AbilityScores() {
abilityScores["Strength"] = Ability("Strength", ...);
abilityScores["Charisma"] = Ability("Charisma", ...);
...
}
Ability& AbilityScores::GetAbility(string abilityName) {
// if you don't mind Name() returning "" for unknown abilities...
return abilityScores[abilityName];
// otherwise...
auto iter = abilityScores.find(abilityName);
if (iter == abilityScores.end()) {
iter = abilityScores.emplace(abilityName, 0.0f).first;
}
return iter->second;
}
...
Skill s* = new Skill[2];
s[0] = Skill(&as.GetAbility("Strength"));
s[1] = Skill(&as.GetAbility("Charisma"));
...
Otherwise, return the Ability object by pointer instead:
Ability* AbilityScores::GetAbility(string abilityName) {
for (int i = 0; i < abilityScores.size(); i++) {
if (abilityScores[i].Name() == abilityName) {
return &abilityScores[i];
}
}
return nullptr;
// or:
abilityScores.emplace_back(abilityName, 0.0f);
return &(abilityScores.back());
}
...
Skill s* = new Skill[2];
s[0] = Skill(as.GetAbility("Strength"));
s[1] = Skill(as.GetAbility("Charisma"));
...
I have a set where each element in the set is of type shared_ptr, I want to remove an element from the set, in eclipse the element was actually removed but when I test this in bash with valgrind I get a lot of invalid size mistakes ...
So this made me think that maybe there is a different way to remove element of type shared_ptr ?
Every element in the peoplePointer is a class of certain person:
typedef std::shared_ptr<person> peoplePointer;
class AA {
std::set<peoplePointer> setOfPeople;
public:
// function getName() return name of the person (person is another class)
void removeSomeonefromA(const std::string& name) {
for (std::set<peoplePointer>::iterator it = setOfPeople.begin();it != setOfPeople.end(); it++) {
if(name == (*it).get()->getName()) {
setOfPeople.erase((it));
}
}
}
};
Idea inspired by remove_if equivalent for std::map.
If you are able to use a C++11 or later compiler, you can use:
void removeSomeonefromA(const string& name)
{
for (set<peoplePointer>::iterator it = setOfPeople.begin(); it != setOfPeople.end(); /* Empty */ )
{
if(name == (*it).get()->getName())
{
it = setOfPeople.erase(it);
}
else
{
++it;
}
}
}
If you are required to use a prior compiler version, you can use:
void removeSomeonefromA(const string& name)
{
for (set<peoplePointer>::iterator it = setOfPeople.begin(); it != setOfPeople.end(); /* Empty */ )
{
if(name == (*it).get()->getName())
{
setOfPeople.erase(it++);
}
else
{
++it;
}
}
}
I tried finding an answer but didn't see one for my particular problem. I am using shared pointers for a ternary search tree (to be used for a predictive text algorithm) and am running into some problems using shared pointers.
I've been away from C++ for 5 years, and let me tell you, Java does not help you learn pointers. I've had to relearn pointer material I learned in school 5-6 years ago over the past couple of days, and have successfully managed to destroy my code.
Here is most of the code I have:
// TernarySearchTree.cc
#include "stdafx.h"
#include "ternary_search_tree.h"
//Constructor
TernarySearchTree::TernarySearchTree() {
num_nodes_ = 0;
size_in_memory_ = 0;
root_node_ = nullptr;
}
TernarySearchTree::TernarySearchTree(const TernarySearchTree& other) {
num_nodes_ = other.num_nodes_;
size_in_memory_ = other.size_in_memory_;
TernarySearchTreeNode node;
node = *other.root_node_;
root_node_.reset(&node);
}
//Destructor
TernarySearchTree::~TernarySearchTree() {
}
//operators
TernarySearchTree& TernarySearchTree::operator=(const TernarySearchTree& other) {
//TODO: swap idiom - create a copy of the node then swap the new one with it
//do this first to provide exception safety
TernarySearchTreeNode node;
node = *other.root_node_;
root_node_.reset(&node);
num_nodes_ = other.num_nodes_;
size_in_memory_ = other.size_in_memory_;
return *this;
}
//Convert from string to c-style string
std::vector<char> TernarySearchTree::ConvertStringToCString(std::string str) {
std::vector<char> wordCharacters (str.begin(), str.end());
//remove newlines or tabs
if (wordCharacters.back() == '\n' || wordCharacters.back() == '\t') {
wordCharacters.pop_back();
}
wordCharacters.push_back('\0');
return wordCharacters;
}
//Insert a node
TernarySearchTreeNode TernarySearchTree::InsertNode(TernarySearchTreeNode ¤tNode,
char character,
NodePosition position,
bool isRoot) {
TernarySearchTreeNode newNode;
newNode.set_character(character);
if (!isRoot) {
switch (position) {
case NODE_POS_LEFT:
currentNode.set_left_node(newNode);
break;
case NODE_POS_CENTRE:
currentNode.set_centre_node(newNode);
break;
case NODE_POS_RIGHT:
currentNode.set_right_node(newNode);
break;
default:
break;
}
}
return newNode;
}
//Insert a word
void TernarySearchTree::InsertWord(std::string word) {
std::vector<char> characters = ConvertStringToCString(word);
std::shared_ptr<TernarySearchTreeNode> currentNode = 0;
bool isFirstCharacter = true;
//Add each character to a node while traversing
//Base case where there is no root node
if (!root_node_) {
for(std::vector<char>::iterator it = characters.begin(); it != characters.end(); ++it) {
if (*it != '\0') {
//if it is the first character
//root_node_ is equal to the address of new node
if (isFirstCharacter) {
std::cout << "HIHI";
TernarySearchTreeNode node = InsertNode(*currentNode, *it, NODE_POS_CENTRE, true);
root_node_.reset(&node);
currentNode.reset(&node);
isFirstCharacter = false;
} else {
TernarySearchTreeNode node = InsertNode(*currentNode, *it, NODE_POS_CENTRE, false);
std::cout << std::endl << node.get_character();
currentNode.reset(&node);
}
}
}
//If not base case, then we need to compare each character
} else {
currentNode = root_node_;
for(std::vector<char>::iterator it = characters.begin(); it != characters.end(); ++it) {
if (*it != '\0') {
currentNode.reset(&SetNextNode(*currentNode, *it, *std::next(it, 1)));
} else {
currentNode->set_end_of_word(true);
}
}
}
}
//Recursive function for obtaining/adding the next node when inserting a word
TernarySearchTreeNode TernarySearchTree::SetNextNode(TernarySearchTreeNode ¤tNode, const char currentChar, const char nextChar) {
//If characters match
if (currentChar == currentNode.get_character()) {
//if centre node exists
if (currentNode.get_centre_node()) {
return *(currentNode.get_centre_node());
//Otherwise, create a new node and recall method on that node
} else {
//If not the end of the word, make a new node with the next letter
if (nextChar != '\0') {
return InsertNode(currentNode, nextChar, NODE_POS_CENTRE, false);
} else {
return currentNode;
}
}
//If it is less, follow node on the left
} else if (currentChar < currentNode.get_character()) {
//if left node exists, recursive call
if (currentNode.get_left_node()) {
return SetNextNode(*(currentNode.get_left_node()), currentChar, nextChar);
//Otherwise, create a new node and recall method on that node
} else {
return SetNextNode(InsertNode(currentNode, currentChar, NODE_POS_LEFT, false), currentChar, nextChar);
}
//Otherwise it is bigger, so take right path
} else {
//if right node exists, recursive call
if (currentNode.get_right_node()) {
return SetNextNode(*(currentNode.get_right_node()), currentChar, nextChar);
//Otherwise, create a new node and recall method on that node
} else {
return SetNextNode(InsertNode(currentNode, currentChar, NODE_POS_RIGHT, false), currentChar, nextChar);
}
}
}
//Populate the TST from a word list/file
void TernarySearchTree::PopulateTreeFromTextFile(std::string fileName) {
std::ifstream file;
std::string line;
file.open(fileName);
if (file.is_open()) {
//Assume text file has one word per line
while (std::getline(file, line)) {
InsertWord(line);
}
}
}
//Search
bool TernarySearchTree::SearchForWord(std::string word) {
return false;
}
int _tmain(int argc, _TCHAR* argv[])
{
//Test
TernarySearchTree tst;
//Open file
tst.PopulateTreeFromTextFile("simple.txt");
//start at root and follow some paths
std::cout << tst.get_root_node();
/**std::vector<char> vec;
vec.push_back('a');
vec.push_back('c');
std::vector<char>::iterator it = vec.begin();
std::cout << *std::next(vec.begin(), 1);
std::cout << (*it < 'c');
it++;
std::cout << *std::next(it, 0);
std::cout << (*it < 'c');
**/
return 0;
}
and for the nodes:
/*TST node methods */
#include <iostream>
#include "ternary_search_tree_node.h"
/** ADD COPY CONSTRUCTOR*/
//Constructors
TernarySearchTreeNode::TernarySearchTreeNode() {
character_ = '\0';
end_of_word_ = false;
left_node_ = nullptr;
centre_node_ = nullptr;
right_node_ = nullptr;
}
TernarySearchTreeNode::TernarySearchTreeNode(const TernarySearchTreeNode& other) {
character_ = other.character_;
end_of_word_ = other.end_of_word_;
TernarySearchTreeNode leftNode;
leftNode = *other.left_node_;
left_node_.reset(&leftNode);
TernarySearchTreeNode centreNode;
centreNode = *other.centre_node_;
centre_node_.reset(¢reNode);
TernarySearchTreeNode rightNode;
rightNode = *other.right_node_;
right_node_.reset(&rightNode);
}
TernarySearchTreeNode::TernarySearchTreeNode(char character, bool end_of_word,
TernarySearchTreeNode left_node,
TernarySearchTreeNode centre_node,
TernarySearchTreeNode right_node) {
character_ = character;
end_of_word_ = end_of_word;
left_node_.reset(&left_node);
centre_node_.reset(¢re_node);
right_node_.reset(&right_node);
}
//Destructor
TernarySearchTreeNode::~TernarySearchTreeNode() {
left_node_.reset();
centre_node_.reset();
right_node_.reset();
}
//operators
TernarySearchTreeNode& TernarySearchTreeNode::operator=(const TernarySearchTreeNode& other) {
if (&other) {
TernarySearchTreeNode leftNode;
leftNode = *other.left_node_;
TernarySearchTreeNode centreNode;
centreNode = *other.centre_node_;
TernarySearchTreeNode rightNode;
rightNode = *other.right_node_;
left_node_.reset(&leftNode);
centre_node_.reset(¢reNode);
right_node_.reset(&rightNode);
character_ = other.character_;
end_of_word_ = other.end_of_word_;
}
return *this;
}
//printing
std::ostream& operator<<(std::ostream& os, const TernarySearchTreeNode& obj)
{
// write obj to stream
char c = obj.get_character();
bool b = obj.is_end_of_word();
os << c << "\t is end of word: " << b;
return os;
}
When I run in debug mode (Visual Studios), it is able to set the root node, but when it goes to input the second node, it crashes trying to delete "stuff" when currentNode calls .reset(&node) within the else statement of function InsertWord. Am I doing something wrong in the copy constructors or operator= methods, or the destructors? The cout line above it does print the correct letter, so it looks like the node is getting created properly.
The debug call stack shows:
TernarySearchTree.exe!std::_Ref_count_base::_Decref() Line 118 C++
TernarySearchTree.exe!std::_Ptr_base::_Decref()
Line 347 C++
TernarySearchTree.exe!std::shared_ptr::~shared_ptr()
Line 624 C++
TernarySearchTree.exe!std::shared_ptr::reset()
Line 649 C++
TernarySearchTree.exe!TernarySearchTreeNode::~TernarySearchTreeNode()
Line 50 C++ TernarySearchTree.exe!TernarySearchTreeNode::`scalar
deleting destructor'(unsigned int) C++
TernarySearchTree.exe!std::_Ref_count::_Destroy()
Line 161 C++ TernarySearchTree.exe!std::_Ref_count_base::_Decref()
Line 120 C++
TernarySearchTree.exe!std::_Ptr_base::_Decref()
Line 347 C++
TernarySearchTree.exe!std::shared_ptr::~shared_ptr()
Line 624 C++
TernarySearchTree.exe!std::shared_ptr::reset()
Line 649 C++
TernarySearchTree.exe!TernarySearchTreeNode::~TernarySearchTreeNode()
Line 50 C++
TernarySearchTree.exe!TernarySearchTree::InsertWord(std::basic_string,std::allocator
word) Line 105 C++ TernarySearchTree.exe!TernarySearchTree::PopulateTreeFromTextFile(std::basic_string,std::allocator
fileName) Line 182 C++ TernarySearchTree.exe!wmain(int argc, wchar_t * * argv) Line 200 C++
TernarySearchTree.exe!__tmainCRTStartup() Line 533 C
TernarySearchTree.exe!wmainCRTStartup() Line 377 C
kernel32.dll!7592338a() Unknown [Frames below may be incorrect
and/or missing, no symbols loaded for kernel32.dll]
ntdll.dll!77599f72() Unknown ntdll.dll!77599f45() Unknown
Thanks for any help you can provide! And let me know if there is anythign else you need me to provide (the text file I am reading in just has the word cornin it).
Your problem is that you're using Java style in C++. Unlike in Java where everything is essentially a pointer, in C++ you have to think about the difference between values, references, pointers, and object lifetime.
This function is bad:
TernarySearchTreeNode::TernarySearchTreeNode(char character, bool end_of_word,
TernarySearchTreeNode left_node,
TernarySearchTreeNode centre_node,
TernarySearchTreeNode right_node) {
character_ = character;
end_of_word_ = end_of_word;
left_node_.reset(&left_node);
centre_node_.reset(¢re_node);
right_node_.reset(&right_node);
}
You are taking TernarySearchTreeNode objects by value, then putting their address into a shared_ptr. The point of a shared_ptr to to take ownership of a dynamically allocated object (one created using new) and delete it when the reference count goes to zero. The objects above (left_node, etc) are stack objects that will go out of scope at the end of the function. When you put their address into a shared_ptr, it will then try to delete those objects later, but they no longer exist.
As far as recommending how to fix this, there is a whole lot going on here where the assumptions are just off. For instance, can a child node have more than one parent? Does it actually make sense to copy nodes?
I'll assume for the moment that copying nodes makes sense, so using shared_ptr is reasonable. In that case we might start here:
TernarySearchTreeNode TernarySearchTree::InsertNode(std::shared_ptr<TernarySearchTreeNode currentNode>,
char character,
NodePosition position,
bool isRoot) {
auto newNode = std::make_shared<TernarySearchTreeNode>();
newNode->set_character(character);
if (!isRoot) {
switch (position) {
case NODE_POS_LEFT:
currentNode->set_left_node(newNode);
Then all of your functions like set_left_node should also take std::shared_ptr<TernarySearchNode> as parameters. You should not be calling reset(), which exists to allow a shared_ptr to take ownership (refcount == 1) of a free pointer. shared_ptr works by incrementing the reference count on copy and dereferencing in the destructor. When you dereference the pointer and then take the address, you are working around the shared_ptr.
The following code instead of returning a pointer back to an audioResource it returns
something else which is invalid, i've gone through with a debugger and the problem is with this line
return *list_it;
Here is my function:
AudioResource* AudioManager::getResource(const unsigned int ID)
{
std::list<AudioResource*>::iterator list_it;
for(list_it = m_resources.begin(); list_it!= m_resources.end(); list_it++)
{
if((*list_it)->getID()==ID)
{
std::cout<<*(*list_it)->getFileName();
return *list_it;
}
}
return nullptr;
}
O and I have tried putting it as (*list_it) but i got the same results =s
How it is populated...
Resource* AudioManager::addResource(const unsigned int ID,
const std::string fileName, const unsigned int scope,
const std::string type)
{
AudioResource* temp;
if(type == "AUDIO_TYPE_SAMPLE")
{
temp = new AudioResource(ID,fileName,scope,
RESOURCE_AUDIO,AUDIO_TYPE_SAMPLE);
m_resources.push_back(temp);
}
else if(type == "AUDIO_TYPE_STREAM")
{
temp = new AudioResource(ID,fileName,scope,
RESOURCE_AUDIO,AUDIO_TYPE_STREAM);
m_resources.push_back(temp);
}
return temp;
}
call to get resource
cout<<AudioManager::getInstance()->getResource(IDnum)->getFileName();
If type is neither of the two values an uninitialized pointer is added to m_resources:
AudioResource* temp;
if(type == "AUDIO_TYPE_SAMPLE")
{
temp = new AudioResource(ID,fileName,scope,RESOURCE_AUDIO,AUDIO_TYPE_SAMPLE);
}
else if(type == "AUDIO_TYPE_STREAM")
{
temp = new AudioResource(ID,fileName,scope,RESOURCE_AUDIO,AUDIO_TYPE_STREAM);
}
m_resources.push_back(temp);
Initialize temp to NULL and only add to m_resources if temp != NULL.
Also, the function returns the same uninitialized pointer.
You return nullptr in case the ID doesn't exist, but you never check against it at the call site, which will give you a null pointer access if the ID doesn't exist and which will likely create problems.
AudioManager::getInstance()->getResource(IDnum)->getFileName();
Change that to
AudioResource* res = AudioManager::getInstance()->getResource(IDnum);
if(res)
std::cout << res->getFileName();