Terminate called after throwing an instance of 'std::bad_alloc' what(): std::bad_alloc

Question

Problem :

I have written the code to perform the following tasks in the order in which they are stated:

1.    Read the input file and count the number of entries in it

2.    Create the array of appropriate size (size equal to number of entries)

3.    Go back to the starting of the input file and read it again

4.    Store the entries in the array

5.    Print out number of entries in your file and the entries themselves.

 

But when I try to execute the .cpp file I keep facing the following error message:

terminate called after throwing an instance of 'std::bad_alloc'

what(): std::bad_alloc

Aborted (core dumped)

I have tried to gather information and came to conclusion that this has to do with a memory shortage or the variables falling out of the main() method, but I am unable to figure out how to solve problem in this specific situation. Please Note: I am working on a Linux computer.

Answer 1

This code must have 3 mistakes:

First mistake: int numEntries. Later you do: ++numEntries;

You are incrementing the unspecified value. Not sure if it's the root cause, but still unacceptable.

Second and third mistake:

const int length = numEntries;

int* arr = new int[length];

And

const int size = numEntries;

int matrix[size];

Your numEntries has the unspecified value (first mistake). You are using it to initialize the length and size now this is Undefined Behaviour. Let us consider it is just some big number - you are allocating memory of unspecified size, So the std::bad_alloc exception - it means you are trying to allocate more memory than you have available.

Also the matrix is a VLA of unspecified size, which is both the non-standard and Undefined behaviour.

Answer 2

Sometimes we face this error while coding. Today we will learn why this error shows and how to solve this problem.

This error indicates that you are running out of memory. It has typically been seen in cases where the hypothesis used for the search contains a large number of sites or a large number of identical sites. Using partial matching for large hypotheses may also contribute to the error: for example, asking that the search must match 6 out of 17 sites. The workaround is to reduce the number of sites in the hypothesis.

The problem shows in your code when you store the memory address of a local variable (local to a function, for example) in a global variable. You can't store the memory address of a local variable in a global variable

Example:

RectInvoice rect(vect,im,x, y, w ,h);
this->rectInvoiceVector.push_back(&rect);

There, &rect is a temporary address (stored in the function's activation registry) and will be destroyed when that function end.

The code should create a dynamic variable:

RectInvoice *rect =  new RectInvoice(vect,im,x, y, w ,h);
this->rectInvoiceVector.push_back(rect);

There you are using a heap address that will not be destroyed in the end of the function's execution.