I was wondering what does this function do and what could be the possible output of this code?
void TreeType::Function()
{
Queue<TreeNode*> q;
TreeNode* node;
if (root!= NULL) {
q.Enqueue(root);
do {
q.Dequeue(node);
cout << node->info << endl;
if (node->left)
{ q.Enqueue(node->left); }
if (node->right)
{ q.Enqueue(node->right); }
while (!q.IsEmpty()); }
this function is like level order traversal of any tree.
while there are many ending semi colons missing.
Related
I am having problems saving the JSON response using json cpprestsdk so that I can pass it back to the calling function. The parse() function seems to do a shallow copy rather than a deep copy. Can someone please help me with the method that I should be using to make a deep copy of the results returned?
Thanks in advance.
functionA()
{
web::json::value myJsonObjSv;
http_client client(L"http://url.com:8080/getdata");
return client.request(methods::GET).then([](http_response response) -> pplx::task<json::value> {
if(response.status_code() == status_codes::OK) {
return response.extract_json();
}
return pplx::task_from_result(json::value()); }).then([&myJsonObjSv](pplx::task<json::value> previousTask) {
try {
// capture json response to json_resp
json::value const resp = previousTask.get();
// Now save the JSON object to return from this function
myJsonObjSv = json::value::parse(resp.serialize());
// This statement displays the contents of myJsonObjSv to be the same as resp
wcout << "myJsonObjSv[" myJsonObjSv.serialize() << "]" << endl;
}
catch( const http_exception& e) {
// print error
}
});
// This statement to display the contents of myJsonObjSv crashes since there was a shallow copy made rather than a deep copy
wcout << "myJsonObjSv[" myJsonObjSv.serialize() << "]" << endl;
}
My JSON is this:
{
"apps":[
{
"id":"x",
"val":"y",
}
]
}
I can get id's value "x" by looping, and exiting when it.first is id:
for (const ptree::value_type &app : root.get_child("apps"))
{
for (const ptree::value_type &it : app.second) {
if (it.first == "id") {
std::cout << it.second.get_value<std::string>().c_str() << std::endl;
}
}
}
What I want, however, is to get the id's value by something like this:
std::cout << root.get<std::string>("apps[0].id").c_str() << std::endl;
Of course this displays nothing to me, for I am probably using wrong syntax accessing 1st element of the apps array. It might be that this has to be done in a different way all together.
I have found only this ugly and dangerous method:
std::cout << root.get_child("apps").begin()->second.begin()->second.get_value<std::string>().c_str() << std::endl;
I cannot really use it this way as it won't throw an exception when the array is empty, it will core dump!
Below is the whole program to make it easier for any one who wants to help:
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>
using boost::property_tree::ptree;
int main()
{
std::stringstream ss("{\"apps\":[{\"id\":\"x\",\"val\":\"y\"}]}");
ptree root;
read_json(ss, root);
for (const ptree::value_type &app : root.get_child("apps"))
{
for (const ptree::value_type &it : app.second) {
if (it.first == "id") {
std::cout << it.second.get_value<std::string>().c_str() << std::endl;
}
}
}
std::cout << root.get_child("apps").begin()->second.begin()->second.get_value<std::string>().c_str() << std::endl;
return 0;
}
As the docs say, array elements are nodes with "" keys.
If you're after the first element, you're in luck:
root.get("apps..id", "")
The .. in the path selects the first empty key
Live On Coliru
#include <boost/property_tree/json_parser.hpp>
#include <iostream>
using boost::property_tree::ptree;
int main() {
std::stringstream ss(R"({"apps":[{"id":"x","val":"y"}]})");
ptree root;
read_json(ss, root);
std::cout << root.get("apps..id", "") << "\n";
}
BONUS
If you need to address elements other than the first, write a helper function. This would be a good start:
#include <string>
#include <stdexcept> // std::out_of_range
template <typename Tree>
Tree query(Tree& pt, typename Tree::path_type path) {
if (path.empty())
return pt;
auto const head = path.reduce();
auto subscript = head.find('[');
auto name = head.substr(0, subscript);
auto index = std::string::npos != subscript && head.back() == ']'
? std::stoul(head.substr(subscript+1))
: 0u;
auto matches = pt.equal_range(name);
if (matches.first==matches.second)
throw std::out_of_range("name:" + name);
for (; matches.first != matches.second && index; --index)
++matches.first;
if (index || matches.first==matches.second)
throw std::out_of_range("index:" + head);
return query(matches.first->second, path);
}
Here's some live tests using it:
Live On Coliru
#include <boost/property_tree/json_parser.hpp>
#include <iostream>
using boost::property_tree::ptree;
int main() {
std::stringstream ss(R"({
"apps": [
{
"id": "x",
"val": "y",
"id": "hidden duplicate"
},
{
"id": "a",
"val": "b"
}
]
})");
ptree root;
read_json(ss, root);
for (auto path : {
"apps..id", "apps.[0].id", // (equivalent)
//
"apps.[0].id[]", // invalid
"apps.[0].id[0]", // x
"apps.[0].id[1]", // hidden duplicate
"apps.[1].id", // a
"apps.[1].id[0]", // a
"apps.[1].id[1]", // out of range
"apps.[2].id", // out of range
"drinks" // huh, no drinks at the foo bar
}) try {
std::cout << "Path '" << path << "' -> ";
std::cout << query(root, path).get_value<std::string>() << "\n";
} catch(std::exception const& e) {
std::cout << "Error: " << e.what() << "\n";
}
}
Prints:
Path 'apps..id' -> x
Path 'apps.[0].id' -> x
Path 'apps.[0].id[]' -> Error: stoul
Path 'apps.[0].id[0]' -> x
Path 'apps.[0].id[1]' -> hidden duplicate
Path 'apps.[1].id' -> a
Path 'apps.[1].id[0]' -> a
Path 'apps.[1].id[1]' -> Error: index:id[1]
Path 'apps.[2].id' -> Error: index:[2]
Path 'drinks' -> Error: name:drinks
current_user pointer works within functions of System.cpp, but resets afterwards. The current_user seems to be updated locally when it's set within the function createUser(string name) when it's called in the switch statement. However, when I try to call it outside the function it seems to have not been updated at all. Not entirely sure what's going on.
Main.cpp
#include <iostream>
#include "System.h"
#include "User.h"
using namespace std;
int main()
{
System s;
s.run();
// Works
User a("Test");
User b("Test 2");
User c("Test 3");
User* current = &a;
cout << "The current user is: " << current->getName() << endl;
current = &b;
cout << "Now it's: " << current->getName() << endl;
current = &c;
cout << "The final current user is: " << current->getName() << endl;
// Does not work
cout << "Current user: " << s.getCurrentUser()->getName() << endl;
}
System.h
#ifndef SYSTEM_H
#define SYSTEM_H
#include "User.h"
#include "Group.h"
#include "MessageBuffer.h"
#include "Banner.h"
#include <iostream>
#include <vector>
class System
{
public:
System();
char validInput(std::string inputIn);
bool validUsername(std::string nameIn);
bool userExists(std::string nameIn);
void createUser(std::string nameIn);
void run();
User* getCurrentUser();
private:
User* current_user;
std::vector<User> user_list;
std::vector<Group> group_list;
};
#endif // SYSTEM_H
System.cpp
// Program 1: TigerBook Social Network
// File: System.cpp
// Description: Class Implimentation of the System Class. Instantiates objects that must be initialized and handles
// basic user screw-ups (choosing and option out of bounds).
#include <iostream>
#include "System.h"
using namespace std;
// Function: Default System Constructor
// Inputs: None
// Description: Default constructor for the class.
System::System()
{
}
User* System::getCurrentUser()
{
return current_user;
}
// Function: validInput
// Inputs: string inputIn
// Outputs: char value of input at 0
// Description: Determines whether the input is valid.
char System::validInput(string inputIn)
{
if (inputIn.length() == 1)
{
return inputIn[0];
}
else
{
return '0';
}
}
// Function: validUsername
// Inputs: string username
// Outputs: true if valid, false if not
// Description: Determines whether the username is valid
bool System::validUsername(string nameIn)
{
if (nameIn.empty() || nameIn.length() < 2 || (nameIn.find_first_not_of("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ") != string::npos))
{
cerr << "\n\t*** ERROR: Invalid user name, please try again! ***" << endl;
return false;
}
else
{
return true;
}
}
// Function: userExists
// Inputs: string username
// Outputs: true if exists, false if not
// Description: Determines whether the username exists in user_list.
bool System::userExists(string nameIn)
{
return false;
}
// Function: createUser
// Inputs: string username
// Outputs: void
// Description: Creates new user and adds it to user_list.
void System::createUser(string nameIn)
{
User u(nameIn);
user_list.push_back(u);
current_user = &u;
}
// Function: run
// Inputs: None
// Outputs: void
// Description: Program driver, handles basic user input and screw-ups
void System::run()
{
//current_user = NULL;
Banner banner("The TigerBook Social Network!");
cout << banner.getBanner() << endl;
bool quit = false;
string input;
while(!quit)
{
cout << "\nCreate new user (n), Broadcast (b), Multicast (m), Unicast (u), Wall page (w), Home page (h), Create new group (g), " << endl;
cout << "Join a group (j), Switch user (s), Quit (q)\n" << endl;
cout << "Choose an option: ";
getline(cin, input);
if (current_user == NULL && (input != "N" && input != "n" && input != "Q" && input != "q"))
{
cerr << "\n\t*** ERROR: There is no current user, please create a new user! ***" << endl;
continue;
}
switch (validInput(input))
{
// Create new user
case 'N':
case 'n':
{
string username;
cout << "\nPlease enter user name: ";
getline(cin, username);
if (!validUsername(username))
{
continue;
}
else if (userExists(username))
{
cerr << "\n\t*** ERROR: The user \"" + username + "\" already exists, please try again! ***" << endl;
continue;
}
else
{
createUser(username);
cout << "\nCurrent user: " << getCurrentUser()->getName() << endl; // test current_user
}
break;
}
case 'B':
case 'b':
{
break;
}
case 'M':
case 'm':
{
break;
}
case 'U':
case 'u':
{
break;
}
case 'W':
case 'w':
{
break;
}
case 'H':
case 'h':
{
break;
}
case 'G':
case 'g':
{
break;
}
case 'J':
case 'j':
{
break;
}
case 'S':
case 's':
{
break;
}
case 'Q':
case 'q':
{
quit = true;
banner.setBanner("Thank you for using TigerBook Social Network!");
cout << banner.getBanner() << endl << endl;
break;
}
default:
{
cerr << "\n\t*** ERROR: Invalid input, please try again! ***" << endl;
}
} // End of switch statement
} // End of loop
}
User.h
#ifndef USER_H
#define USER_H
#include <string>
class User
{
public:
User();
User(std::string nameIn);
std::string getName();
void setName(std::string nameIn);
private:
std::string name;
};
#endif // USER_H
User.cpp
// Program 1: TigerBook Social Network
// File: User.cpp
// Description: Class implementation for User class
#include "User.h"
using namespace std;
// Constructor (Default)
User::User()
{
//ctor
}
// Constructor
// Inputs: string that sets name
// Description: Constructs user object and assigns its name.
User::User(string nameIn)
{
name = nameIn;
}
// Function: setName
// Inputs: string that sets name
// Outputs: void
// Description: Sets name of user object.
void User::setName(string nameIn)
{
name = nameIn;
}
// Function: getName
// Inputs: none
// Outputs: Name of user
// Description: Returns the name of the user object.
string User::getName()
{
return name;
}
You have:
void System::createUser(string nameIn)
{
User u(nameIn);
user_list.push_back(u);
current_user = &u;
}
Here, you are storing pointer to a local variable. The pointer becomes a dangling pointer as soon as the function returns. Any use of current_usr to access the object after the function returns is cause for undefined behavior.
You can use:
void System::createUser(string nameIn)
{
User u(nameIn);
user_list.push_back(u);
current_user = &(user_list.back());
}
Even that is very fragile. It will work if you carefully manage the objects in user_list.
A better option will be not to store a pointer to the object at all. You can, for example, use:
User* System::getCurrentUser()
{
if ( user_list.empty() )
{
return nullptr;
}
return &(user_list.back());
}
I have an output of a string that is:
I need to print out only the parts that are between"tele": and then the ",". for example the first one i need to print out is hel. In the above string output. "text":"hel","source": is the first part. Every where there is a "tele": and the "," i need to be printed.
the code i have written so far prints out only the first one and is shown below
int comm_poss;
string econ;
tax= mes.find("tele");
econ=mes.substr(tax,15);
cout<<"msg test : "<<econ;
This prints out tele":"hel"," but not the other part that is between the "tele" and ","
how do i print only whats between those two and make the code do it multiple times?
thanks
EDIT: the other part in the output is "tele":"FIRS","code":" found near the end
Save yourself some trouble and use a JSON parser. For example using JsonCpp library and reading the JSON file from stdin (untested):
Json::Value root;
std::cin >> root;
for (int i = 0; i < root.size(); i++) {
std::string text = root[i]["text"].asString();
std::cout << text << std::endl;
}
Could something like this help.
string txt_test;
size_t poss_text;
poss_text= replyMsg.find("text:\":\""); // Search for text":"
replyMsg=replyMsg.substr(poss_text + 8); // Get rest of string
// Add 8 to get beyond text":"
poss_text= replyMsg.find("\","); // Search for ",
txt_test = replyMsg.substr(0, poss_text); // Get from start to ",
cout<< "msg test : " << txt_test;
You should however always check whether your string were found:
if (poss_text != std::string::npos)
{
// Found - so go on
}
else
{
// Not found - stop now
}
Now you can add the loop:
int main()
{
string replyMsg = "HEJtext:\":\"first\",\"hhhtext:\":\"second\",";
string txt_test;
size_t poss_text = 1;
while(poss_text != std::string::npos) // Loop while there is still something in replyMsg
{
poss_text= replyMsg.find("text:\":\""); // Search for text":"
if (poss_text != std::string::npos)
{
replyMsg=replyMsg.substr(poss_text + 8); // Get rest of string
// Add 8 to get beyond text":"
poss_text= replyMsg.find("\","); // Search for ",
if (poss_text != std::string::npos)
{
txt_test = replyMsg.substr(0, poss_text); // Get from start to ",
cout<< "msg test : " << txt_test << std::endl ;
replyMsg=replyMsg.substr(poss_text); // Prepare for next search
}
}
}
return 0;
}
This is a working solution.
I will not use any library since you probably want to know how to do it from scratch.
1. Using Strtok() with delim(':') and checking if the 6 characters to
the left is equal to "text", If TRUE, then pickup all characters to the right
until you hit ",".
2. When you're picking up characters to the right, to avoid reading past your domain, modify the content string by adding a '$' symbol to the end.
#include <iostream>
void get_text(char * token);
int main(){
char =content[]="586162004425048066\",\"text\":\"hel\",\"source\":...\"text\":\"yo\";$";
char * token;
token=strtok(content,":");
get_text(token);
while(token=strtok(NULL,":")){
get_text(token);
}
}
void get_text(char * token){
unsigned int len=strlen(token);
std::string temp;
if (len>=6){ // Reading the 6 characters to the left and storing it in temp
for (int i=-6; i<0; i++){
temp=temp+token[len+i];
}
}
if (temp=="\"text\""){
temp="";
unsigned i=len;
while(token[i]!=',' and token[i]!='$'){ // retrieve characters to the right until you hit a ',' or '$' (which indicates end of line as a boundary condition)
temp=temp+token[i];
i++;
}
std::cout<<temp;
}
}
OUTPUT
"hey" "yo"
Suppose I have a double Eigen matrix and I want to write it to a csv file. I find the way of writing into a file in raw format but I need commas between entries. Here is the code I foudn for simple writing.
void writeToCSVfile(string name, MatrixXd matrix)
{
ofstream file(name.c_str());
if (file.is_open())
{
file << matrix << '\n';
//file << "m" << '\n' << colm(matrix) << '\n';
}
}
Using format is a bit more concise:
// define the format you want, you only need one instance of this...
const static IOFormat CSVFormat(StreamPrecision, DontAlignCols, ", ", "\n");
...
void writeToCSVfile(string name, MatrixXd matrix)
{
ofstream file(name.c_str());
file << matrix.format(CSVFormat);
}
Here is what I came up;
void writeToCSVfile(string name, MatrixXd matrix)
{
ofstream file(name.c_str());
for(int i = 0; i < matrix.rows(); i++){
for(int j = 0; j < matrix.cols(); j++){
string str = lexical_cast<std::string>(matrix(i,j));
if(j+1 == matrix.cols()){
file<<str;
}else{
file<<str<<',';
}
}
file<<'\n';
}
}
This is the MWE to the solution given by Partha Lal.
// eigen2csv.cpp
#include <Eigen/Dense>
#include <iostream>
#include <fstream>
// define the format you want, you only need one instance of this...
// see https://eigen.tuxfamily.org/dox/structEigen_1_1IOFormat.html
const static Eigen::IOFormat CSVFormat(Eigen::StreamPrecision, Eigen::DontAlignCols, ", ", "\n");
// writing functions taking Eigen types as parameters,
// see https://eigen.tuxfamily.org/dox/TopicFunctionTakingEigenTypes.html
template <typename Derived>
void writeToCSVfile(std::string name, const Eigen::MatrixBase<Derived>& matrix)
{
std::ofstream file(name.c_str());
file << matrix.format(CSVFormat);
// file.close() is not necessary,
// desctructur closes file, see https://en.cppreference.com/w/cpp/io/basic_ofstream
}
int main()
{
Eigen::MatrixXd vals = Eigen::MatrixXd::Random(10, 3);
writeToCSVfile("test.csv", vals);
}
Compile with g++ eigen2csv.cpp -I<EigenIncludePath>.