C++ :: Transverse Vector Of Structs - Null Pointer
Mar 14, 2014
struct mystruct{
int n;
};
class mscope{
public:
std::vector<mystruct> mv;
[Code] .....
So I have a vector of structs and I want to traverse it, find a struct that matches a constraint and obtain a pointer to that struct. I made a function for this purpose which takes a number and an empty pointer that will store the reference. However, after function returns the pointer becomes null. What could be causing this?
How to fill a vector with structs that are read in from a separate file. Each line in the file would read for example "Doe John M 26" for the name of the person, gender and age. I just need to get pointed in the right direction so I can get this started.
what I am trying to do is to pass to a function the address of an array of structs, so I can later modify the items within the struct, within the array
Code: typedef struct { //A struct of name auctionint bidder;float bid;} auction; void myFunction (auction * auctionItem[]){(*aucItem[x]).bid = y;(*aucItem[x]).bidder = z;} int main(){auction theItems[10]; myFunction(theItems);} Where x, y, and z can be any number.
When I try to run my code the IDE (I'm using Code::Blocks 12.11) does not give me any errors, but it does give me a warning:
warning: passing argument 3 of '<function name>' from incompatible pointer type [enabled by default]
and the note:
note: expected 'struct <struct name> **' but argument is of type 'struct <struct name> *'.Also, when I run the program, it will crash and return garbage.
When I try to run this, I only get the message "Material pointer is null". So, somehow the pointer is null after the hitObjects-function is called, even though it isn't inside that function.
So I'm writing a small program for class, and for some reason I keep getting an error when trying to initialize head to NULL. Even threw in the namespace just to see, nothin'.
#ifndef NUMBERLIST_H #define NUMBERLIST_H using namespace std;
[Code].....
There's my header file. Not sure what I'm doing wrong with the constructor.
EDIT: Got it to work with nullptr, but still curious why that isn't working
In jumping into C++ it says something like this: It's not necessary but when you delete a pointer it's a good idea to reset it as a null pointer. That if your code try's to dereference the pointer after being freed, your program will crash. This happens to a lot of experienced programmers.
This could corrupt users data. delete p_int; p_int = NULL;
1. If you can deference a pointer after the memory is freed, why can't you just delete the pointer?
2. If you can do 1, how do you delete the pointer using code?
3. Every thing I've read says that free memory is handed out in a sequenced order. I don't believe that is true at all. I may be wrong. Why can't you put the data in any number of places if it will fit. Isn't the compiler smart enough to know where bytes (bits)and pieces are stored?
4. If you storing anything in free memory must use a pointer to it?
5. Can a pointer or something similar be used with stack memory?
in the below program for both class pointers pointing to null. Class contains normal function executing but class contains virtual function getting segmentation fault.
m_gradient() constructor is called to construct m_gradient, which in turns sets a variable called m_S to NULL(0), then in the assignment operator, because the m_S is NULL, Visual Studio throws an exception saying that destination pointer is null, but it's not fatal. I don't like that to happen because I have to press ignore many many times when the program is debugged, how can I fix this bug (not mine) to avoid the null destination pointer exception?
As an intermediate layer, the function calls boost unbounded array operator = which in turns calls std::copy which results in this error
lets say I have a pointer p_unit of type c_unit* (c_unit is an a.b.c.)
I have a function that returns a pointer to a new c_unit object:
c_unit * man_add_unit() { c_unit * local_p_unit; unsigned short int local_run_code; print_man_add_menu(); local_run_code = get_a_run_code(); // this bit just gets user input switch (local_run_code)
[code]....
I assign that to p_unit, then add it to a vector v_units:
p_unit = man_add_unit(); v_units.push_back(p_unit); cout << "New unit added. ";
The whole program runs on a loop, and another thing the user can do is to print out data on c_unit objects pointed to by v_units. The problem is, in that function up there ^ I give the user the option to go back to main menu without creating a unit.
Since "local_p_unit" is declared but not assigned an initial value, I'm guessing the function would return a "null" pointer (which is what's hanging me up). If I just let this run with the above code, and go to print out the unit data, the program crashes.
I tried to make an if thing with p_unit == 0 but this always returns false and doesn't catch the "bad" unit that will subsequently cause a crash.
Btw, I have considered assigning a reference to a generic c_unit object to that there local_p_unit so it won't return null, then remove pointers to that object from v_units at the end of the loop.. But I know there's got to be a better way.
getting an invalid null pointer error message after a successful build. This program is supposed to ask for firstName, lastName, age and maJor and keep doing so until the age that is input is 0 and then the program closes. Here is what I have.
#include <iostream> #include <string> using namespace std;
I am having a lot of trouble being able to get data from a file and input it into given structs and arrays of structs and then outputting the file. We are given a file that contains 96 lines and looks like this:
Arzin, Neil 2.3 6.0 5.0 6.7 7.8 5.6 8.9 7.6 Babbage, Charles 2.3 5.6 6.5 7.6 8.7 7.8 5.4 4.5
This file continues for 24 different people and then repeats with different scores (the second line). The first number, in this case is 2.3 for both people is a difficulty rating. The next 6 numbers are scores.
We are given this data in order to set up our structs and arrays and my code:
#include <iostream> #include <fstream> #include <iomanip> #include <string> #include <cmath> using namespace std; int main () { ifstream inFile; inFile.open("C://diveData.txt);
I am looking at one of the functions of an exercise:
void escape(char * s, char * t) { int i, j; i = j = 0; while ( t[i] ) { /* Translate the special character, if we have one */ switch( t[i] ) {
[code]...
Notice the while loop evaluates the current value in t to true or false. When we hit the null terminator, does that get evaluated as 0 and hence evaluates as a falsy value so the while loop exits?
i need a function that will work for both dynamic and static implementations of a function to get the transverse of a matrix. so far, i have this
Code:
matrix transpose(matrix m) { int row, col; row = m.com_dim; col= m.row_dim; }
[code]....
this works well with my static implementation, but when i try it in dynamic it gives me errors. the function has to be the same for both dynamic and static implementation
My problem is that I have two classes that both need members from each other, so I need to use forward declaration + pointers, etc. However, trying to access a vector from a pointer throws an error.
level is a pointer to class Level. This function is inside class GamePiece. Class Level includes class GamePiece, but GamePiece needs access to the vector CollisionObjects. This function throws a vector size error, and I'm totally lost on what to do.
I passed the address of the vector to the function. And then display the address. It is a pretty common operation. But it just won't work. But then we do something simple similar to that of the vector. But it works.
When you login to my site my loginservice which is done by ajax and json make a session called context.Session["Name"]. With BreakPoints it shows that everything is good and the variables are in place. However when I use Session["Name"] it comes out as null.
I will add my code at the bottem not
using System; using System.Collections.Generic; using System.Linq;
This all compiles ok, but the last line in the code above causes a segmentation fault. I should mention Node is declared on its own in Node.h and what pgm is. including pgm.h in node.
I'm tying to create a program that evaluates all possible actions for a certain problem.
So what i'm basically trying to do is to create a sequence of actions, evaluate them to check if it's the best sequence, change the sequence, evaluate again and so on until all possible scenarios are exhausted, leaving the best one in the end.
My approach to this at first was to create a tree of all possible options and then evaluate each branch. Since there are a lot of possible cases i ran out of memory while the program was still creating the tree. I changed this to create just a branch, evaluate it and then modify it.
I was still getting memory problems. I declared a class tNode and declared a vector<tNode*> branch. Then i created all the nodes i needed for that branch with branch.push_back( new tNode() ). When i wanted to modify the branch i simply used branch.pop_back() and again a branch.push_back( new tNode() ). I figured i was getting the problem because although i clear the vector, i don't actually clear the reference in memory. Is this correct? If so, how can i actually delete the memory space and not just the pointer in the vector?
struct Point {int* a; int b;}; vector<vector<Point> > numbers; vector<int> example;
The numbers vector has a matrix of a sort and each of the members are pointing to one member in the example vector. A member numbers.at(2).at(3).a is pointing at example.at(3). Now, can I remotely delete a member in the example vector using the pointers? Like so:
delete (*(numbers.at(2).at(3).a));
I know there is a more convenient way to delete members, but this is a very specific case I'm working on.
"Write a declaration for a function that takes two int parameters and returns an int, and declare a vector whose elements have this function pointer type."
