I'm working on a school assignment. It is an assignment in which every 2 weeks, we have to either expand or change the layout of it. This week, we are forced to use pointers. I'm having a hard time understanding memory and how to allocate it properly without having segmentation faults.
I've created a struct array which is initialized to a char pointer. Every time i loop, after the 1st loop i get "segmentation faults". I simply don't understand why?
I could include the whole code but according to gdb my issue is pertaining to 1 specific line.
const int arraySize = 100;
int counter = 0;
struct contacts{
char * name;
char * date;
char * note;
};
contacts * contactList[arraySize] =
contactList = new contacts;
for(int i = 0; i <= counter; i++){
contactList[i]->name = new char[20]; //Segmentation Fault here
std::cout << contactList[i]->name << std::endl;
//first 1 outputs = fine
//2nd output = segmentation error
counter++;
}
The code is simplified and minimilized for easy reading. If anyone wants it i can insert the whole code. Just be wary that is relatively big. I have set breakpoint through my code to narrow it down. It has come down to that specific statement. Everything else i perfectly fine, especially since it all compiles perfectly fine.
Any hints or assistance with it can be great.
Also I'm not allowed to use any vectors, strings, etc., only cstrings.
User mentioned that i only create 1 contact.
contacts * contactList[arraySize];
contactList = new contacts;
//Instead it should be like this:
contacts * contactList[arraySize];
contactList = new contacts[arraySize];
Update:
I've tried using what everyone recommended.
contacts* contactList[arraySize];
contactList = new contacts[arraySize];
But i get this error:
error: incompatible types in assignment of‘ContactClass::contacts*’ to ‘ContactClass::contacts* [100]’
Your first problem is in this line:
contacts * contactList[arraySize] = new contacts;
it should be
contacts* contactList = new contacts[arraySize];
next problem is here
for(int i = 0; i <= counter; i++){
should be
for(int i = 0; i < arraysize; i++){
contactList[i].name = new char[20];
}
Related
I've been unsuccessfully trying to create an array of IloModel object. Is there an easy way to do it ?
This is what I've tried so far:
IloModel* models = new(env) IloModel[S];
The code compiles but whenever I try to add constraints to each one of the models, the following error message is displayed:
Error:trying to add to an empty handle IloModel
I've removed the argumento from the new operator and added the following lines to code I'm wrinting:
cout << "0" << endl;
for(int i=0; i < S; S++)
models[i] = IloModel(env);
But now the computer freezes when I run the code.
You are creating an array of empty model objects (i.e. objects without handle). After creating the array of empty models you have to initialize each of the models:
for (int i = 0; i < 5; ++i) models[i] = IloModel(env);
I am not sure about the placement-new syntax for allocating the array. Unless there is a very good reason not to use the default operator new, it is probably easier to read to just us that or even allocate the array on the stack.
EDIT: Here is a full code snippet that works for me:
IloEnv env;
int S = 5;
IloModel *models = new IloModel[S];
for (int i = 0; i < S; ++i)
models[i] = IloModel(env);
When I run my program with valgrind it gives an invalid read and write of size 8 error. I have broke my head over this but I can't see what's going wrong.
The valgrind errors occur in the last and second last lines of this code:
void MLPerceptron::returnOutputActivation(vector<Feature> imageFeatures,vector<double>& outputActivation){
int train = 1;
for (unsigned int i = 0; i<imageFeatures.size();i++){
activations[0] = imageFeatures[i].content;
feedforward(train);
activationsToOutputProbabilities();
setMinActivation(outputActivation,activations[2]);
}
}
void MLPerceptron::setMinActivation(vector<double>& minOutputActivation,vector<double> currentActivation){
for(unsigned int i=0;i<currentActivation.size();i++){
if(minOutputActivation[i] > currentActivation[i])
minOutputActivation[i] = currentActivation[i];
}
}
The vectors are initialized in another function and then given to the function returnOutputActivations, this happens in a different file see here:
void MLPController:: createOutputProbabilitiesVectorTest(vector<vector<Feature> >& testSet){
unsigned int nOutputProbabilities = settings.mlpSettings.nOutputUnits;
vector<double> input;
input.reserve(nOutputProbabilities*nMLPs);
for(int j=0; j<nMLPs; j++){
vector<Feature>::const_iterator first = testSet[j].begin();
vector<Feature>::const_iterator last = testSet[j].begin()+numPatchesPerSquare[j];
vector<double> inputTemp = vector<double>(nOutputProbabilities, 10.0);
mlps[0][j].returnOutputActivation(vector<Feature>(first,last),inputTemp);
input.insert(input.end(),inputTemp.begin(),inputTemp.end());
}
Feature newFeat = new Feature(input);
newFeat.setLabelId(testSet[0][0].getLabelId());
inputTrainSecondLayerMLP.push_back(newFeat);
}
I know that there already a lot of posts about the valgrind error but it didn't help me to figure out what's going wrong.
I think
Feature newFeat = new Feature(input)
is the problem. This will allocate a new Feature on the heap, but you will lose its address and it will thus not be deleted. Use Feature* newFeat = new Feature(input) as per MikeCAT's suggestion.
My homework is that I have to make a class (register) which contains 3 class arrays (birds, mammals, reptiles) which are in the animal class. Animal is the friend of Register. I will only show the birds part, to keep it simple.
The register class looks like:
class Register
{
Bird* birds;
unsigned int birdSize;
public:
...
}
The constructor of register:
Register::Register()
{
this->birds = new Bird[0];
this->birdSize = NULL;
}
Now I have a function in register that adds one element to the birds array, the input is cin.
void Register::add()
{
...
if (birdSize == 0)
{
birds = new Bird[0];
Bird* temp = new Bird[0];
temp[0].add();
this->birds = temp;
birdSize++;
}
else
{
Bird* temp = new Bird[birdSize+1];
for (unsigned int i=0; i<=birdSize; i++)
{
temp[i] = this->birds[i];
}
temp[birdSize+1].add();
birds = new Bird[birdSize+1];
birds = temp;
birdSize++;
}
temp[0].add() has the cin, it works properly. When I run the program, the user has to add 2 birds to the array. The problem occurs when reaching the part under 'else', so the second element of the array. The program surely reaches "temp[birdSize+1].add();" while running, then the "xyz.exe has stopped working" window pops up and it says in the details " Fault Module Name: StackHash_7e8e" so I'm sure something is wrong with the memory allocation, but the problem is that when I try to find the problematic line in debug mode, everything works fine.
Well, not everything. The program has a print() function, it prints out everything in Register. The second element of the array is the same as the first.
I have no clue what to do. I read many forum posts, read a cpp book, watched online tutorials, but I can't find the solution for this problem. Please help.
Array index starts from 0. So in else part you are writing
Bird* temp = new Bird[birdSize+1]; // size =birdSize +1;
So valid index range will be 0 -> birdSize, not birdSize+1.
The problem is
temp[birdSize+1].add();
you are using birdSize+1th index. It should be
temp[birdSize].add();
There are other bugs in your code:
for (unsigned int i=0; i<=birdSize; i++) // should be i<birdSize
{
temp[i] = this->birds[i];
}
There are other bad coding in your program:
Register::Register()
{
this->birds = new Bird[0]; // should be this->birds=NULL
this->birdSize = NULL; // should be this->birdSize = 0
}
And obviously if your homework does not demand it, you should not use arrays in this way. For variable size container, use vector, list.... Array is only when the size is fixed.
As above, I'm trying to create and then fill an array of structures with some starting data to then write to/read from.
I'm still writing the cache simulator as per my previous question:
Any way to get rid of the null character at the end of an istream get?
Here's how I'm making the array:
struct cacheline
{
string data;
string tag;
bool valid;
bool dirty;
};
cacheline **AllocateDynamicArray( int nRows, int nCols)
{
cacheline **dynamicArray;
dynamicArray = new cacheline*[nRows];
for( int i = 0 ; i < nRows ; i++ )
dynamicArray[i] = new cacheline [nCols];
return dynamicArray;
}
I'm calling this from main:
cacheline **cache = AllocateDynamicArray(nooflines,noofways);
It seems to create the array ok, but when I try to fill it I get memory errors, here's how I'm trying to do it:
int fillcache(cacheline **cache, int cachesize, int cachelinelength, int ways)
{
for (int j = 0; j < ways; j++)
{
for (int i = 0; i < cachesize/(cachelinelength*4); i++)
{
cache[i][ways].data = "EMPTY";
cache[i][ways].tag = "";
cache[i][ways].valid = 0;
cache[i][ways].dirty = 0;
}
}
return(1);
}
Calling it with:
fillcache(cache, cachesize, cachelinelength, noofways);
Now, this is the first time I've really tried to use dynamic arrays, so it's entirely possible I'm doing that completely wrong, let alone when trying to make it 2d, any ideas would be greatly appreciated :)
Also, is there an easier way to do write to/read from the array? At the moment (I think) I'm having to pass lots of variables to and from functions, including the array (or a pointer to the array?) each time which doesn't seem efficient?
Something else I'm unsure of, when I pass the array (pointer?) and edit the array, when I go back out of the function, will the array still be edited?
Thanks
Edit:
Just noticed a monumentally stupid error, it should ofcourse be:
cache[i][j].data = "EMPTY";
You should find your happiness. You just need the time to check it out (:
The way to happiness
I'm running CodeBlocks on the MingW compiler in an XP virtual machine. I wrote in some simple code, accessible at cl1p , which answers the algorithm question at CodeChef (Well it only answers it partly, as I have not yet included the loop for multiple test cases.
However, my problem is, that while running it in debug mode, it gives the correct output of 5, for the input:
3
1
2 1
1 2 3
However, when I build and run it, it gives the absurd, huge output 131078, what seems like garbage to me. I do not understand how the hell this is happening, but am guessing it's something to do with the dynamic memory allocation. What's the problem here, and how can I fix it? I even ran it through the online compiler at BotSkool, and it worked fine. After adding the loop for test cases, the code even worked correctly on CodeChef!
#include <iostream>
using namespace std;
int main()
{
// Take In number of rows
int numofrows;
cin >> numofrows;
// Input Only item in first row
int * prevrow;
prevrow = new int[1];
cin >> prevrow[0];
// For every other row
for (int currownum = 1; currownum < numofrows; currownum++)
{
// Declare an array for that row's max values
int * currow;
currow = new int[currownum+1];
int curnum;
cin >> curnum;
// If its the first element, max is prevmax + current input
currow[0] = prevrow[0] + curnum;
// for every element
int i = 1;
for (; i <= currownum; i++)
{
cin >> curnum;
// if its not the first element, check whether prevmax or prev-1max is greater. Add to current input
int max = (prevrow[i] > prevrow[i-1]) ? prevrow[i] : prevrow[i-1];
// save as currmax.
currow[i] = max + curnum;
}
// save entire array in prev
prevrow = new int[i+1];
prevrow = currow;
}
// get highest element of array
int ans = 0;
for (int j=0; j<numofrows; j++)
{
if (prevrow[j] > ans)
{
ans = prevrow[j];
}
}
cout << ans;
}
Run the code through Valgrind on a Linux machine and you'll be amazed at how many places your code is leaking memory.
If you are taking the hard road of managing your memory, do it well and 'delete' all the new-allocated memory before allocating more.
If, on the other hand, you prefer the easy road, use a std::vector and forget about memory management.
For one thing, this:
//save entire array in prev
prevrow = new int [i+1];
prevrow = currow;
copies the pointer, not the whole array.
In your loop, you have this line
int max = (prevrow[i]>prevrow[i-1])?prevrow[i]:prevrow[i-1];
On the first iteration of the main loop, when currownum == 1, the loop containing this line will be entered, as i is initialized to 1. But on the first iteration, prevrow only has one element and this line tries to access prevrow[1]. In a debug build, the memory simply gets initialized to zero, but in a normal build, you get some garbage value that just happened to be in the memory, leading to the result you see.
Pretty much always, when you get garbage values in a normal build, but everything is fine in a debug build, you are accessing some uninitialized memory.
Also, your program is leaking memory like crazy. For instance, you don't need to assign any result of new inside the loop to prevrow because right after that you change prevrow to point to another block of allocated memory. Also, you should call delete for any memory that you are no longer using.