Add elements in vector

[tobiasguimaraes]

Hi!

i'm new to c++, i'm trying to make a for to add elements in my vector, those elements are a custom object named Peer.
i'm using Visual Studio 2015, Win32 Project..
follow my code :

std::vector<Peer*> peers;

for (const Json::Value& json: jsonData["objt"]) {
	const std::string aux(json["label"].asString());
	char label[200];
	strcpy_s(label, aux.c_str());
	Peer *peer = new Peer();
	Peer *child;
	peer->setLabel(label);
//Add in vector
        peers.push_back(peer);
	peer = NULL;
}

Ok, i think this code isnt wrong, after this loop, i tryed to test doing this loop :

for each (Peer *p in peers){
	MessageBox(NULL,p->getLabel(),p->getLabel(),NULL);
}

the size of vector is right, but all elements that return in this second loop are the same.. i dont know what is wrong in this code..
if someone could help my i'll be grateful!

Sorry about my bad english..
Att
Tobias

[Moschops]

for each (Peer *p in peers)
That's no C++ I've ever seen. Some kind of Microsoft extension, I expect. Why not use the standard C++ ranged for loop?

Setting that aside, how do you know what's going into the vector? You don't, for sure, so check:

Before line 11:
cout << "Label on new object: " << peer->getLabel() << endl;

Before line 12.
cout << "Element at back of vector is now: " << peers.back()->getLabel() << endl;

Don't guess; MEASURE.

[tobiasguimaraes]

thanks for the awnser..
i'm using Visual C++..

i checked every insert in vector right after, and it returns me the right label.

std::vector<Peer*> peers;
int i = 0;

for (const Json::Value& json: jsonData["objt"]) {
const std::string aux(json["label"].asString());
	char label[200];
	strcpy_s(label, aux.c_str());
	Peer *peer = new Peer();
	Peer *child;
	peer->setLabel(label);
//Add in vector
        peers.push_back(peer);
//Popup with the right label
        MessageBox(NULL,peers.at(i)->getLabel(),peers.at(i)->getLabel(),NULL);
        i++;
	peer = NULL;
}

//Check if the first element in vector is same of the first popup, but print the last position in vector.
MessageBox(NULL,peers.at(0)->getLabel(),peers.at(0)->getLabel(),NULL);
//dosent matter which position i try to print, always will print the last position of vector 

[ne555]

I'm going to do a blind guess and say that that test will pass, all the output will be what was expected. The problem is in .setLabel() that simply assigns a pointer in Peer instead of copying the content.


> Peer *peer = new Peer();

Peer peer; or better Peer peer(label);

[tobiasguimaraes]

thanks ne55 but still dont work :(

my class peer.cpp

//Peer.cpp

char *label;

{...}

char* Peer::getLabel() {
	return label;
}

void Peer::setLabel(char *nome) {
	label = nome;
}

[ne555]

char *label;
void Peer::setLabel(char *nome) {
	label = nome;
}

that's your mistake.
you need to copy the content, but you are simply pointing to that memory address.

As a fix

class Peer{
private:
   std::string label;
   void Peer::setLabel(const char *nome){ //or ask for a std::string
      label = nome; //this being std::string it will copy the content
   }
   const char* Peer::getLabel() const{
      return label.c_str()
   }
};

//...
const std::string aux(json["label"].asString());
Peer *peer = new Peer(); //this would be better as Peer peer;
peer->setLabel( aux.c_str() );

peers.push_back(peer); //and this vector should be std::vector<Peer> 

[tobiasguimaraes]

Thanks again!

Still dont work..
o changed as you said..

Class Peer{

public :
        const char * getLabel() const;
	void setLabel(const char * nome)
};
//..
std::string label;
const char* Peer::getLabel() const {
	return label.c_str();
}
void Peer::setLabel(const char *nome) {
	label = nome;
}

My loop :

for (const Json::Value& filas : jsonData["filas"]) {
	Peer *peer = new Peer();
	const std::string fila(filas["nome"].asString());
	peer->setLabel(fila.c_str());
	peer->setNumero(NULL);
	peers.push_back(peer);
        //this messagebox shows ok
	//	MessageBox(NULL, peers.at(i)->getLabel(), peers.at(i)->getLabel(),NULL);
	i++;
}

//i made this other for, for test if the results would do the same, but all messages are the last element that i push to vector

for each (Peer *p in peers)
{
    MessageBox(NULL,p->getLabel(),p->getLabel(),NULL);
}

i dont know to do it..

[Moschops]

In the code you showed us, here:

Class Peer{

public :
        const char * getLabel() const;
	void setLabel(const char * nome)
};
//..
std::string label;
const char* Peer::getLabel() const {
	return label.c_str();
}
void Peer::setLabel(const char *nome) {
	label = nome;
}

The std::string named label isn't a class member. It's outside the class.