Question

I’m working on an simple vector program as an assignment, but I cant figure out my why program asserts. My program compiles successfully, but fails at runtime. I think im at the reach of expertise on this one.

#include <iostream>
#include <cstring>
#include <assert.h>
#include <stdio.h>
#include <iomanip>
#define TESTING
using namespace std;
typedef float Elem;//floats for vector elements

struct Vector{//structure for the vector
    unsigned int size;
    Elem *svector;
};


int main(){

#ifdef TESTING
        //prototypes
    Vector *alloc_vec();
    bool print_vec(Vector *printVector);
    Vector *extend_vec(Vector *extend,Elem element);
    Vector *scalar_plus(Vector *vecToAdd, Elem addElement);
    void dealloc_vec(Vector *&deAlloc);

    //testing scaffolds
    Vector *testVec=new Vector;
    *testVec=*alloc_vec();
    assert(testVec->size==0);
    assert(testVec->svector==NULL);

    for(int i=0;i=10;i++){
        *testVec=*extend_vec(testVec,Elem(i));
    }

    assert(testVec->size!=0);
    assert(testVec->svector!=NULL);

    assert(print_vec(testVec));
    print_vec(testVec);

    *testVec=*scalar_plus(testVec,5);

    print_vec(testVec);

    dealloc_vec(testVec);

    assert(testVec==NULL);
#endif //testing

    return 0;
}

Vector *alloc_vec(){//constructor to allocate an empty (zero-length) vector
    Vector *newVector=new Vector; //initiatizes a new vector
        if (newVector==NULL){
        return NULL;
    }

    newVector->size=0;//sets length to 0 
    newVector->svector=NULL;//sets vector to null


    return newVector;
}

bool print_vec(Vector *printVector){

    if(printVector==NULL){//makes sure printVector exists to pass unit test 1
        return false;
    }

    for(unsigned int i=0; i<printVector->size;i++){
        cout<<printVector->svector[i]<<endl;
    }

    return true;

}

void dealloc_vec(Vector *deAlloc){
    if (deAlloc==NULL){//if the vector contains no memory, no need to deallocate, unit test#1
        return;}

    delete deAlloc;//clears the memory of the vector
    deAlloc=NULL;
    return;

}

Vector *extend_vec(Vector *extend,Elem element){
    if (extend==NULL){
        return NULL;}


    Elem *tempVec=new Elem[extend->size+1];//sets up a temp vector one size larger
    tempVec[extend->size]=element;

    memcpy(tempVec,extend->svector,(extend->size*sizeof(Elem)));//copies the memory from the original array to the rest of the temp array

        extend->size+=1;

    delete[] extend->svector;//clears the memory

    extend->svector=tempVec;//the original vector now becomes the extended vector

    delete[] tempVec;//clears the temporary memory

        return extend;
}

Vector *scalar_plus(Vector *vecToAdd, Elem addElement){
    if (vecToAdd==NULL){
        return NULL;}
    for(unsigned int i=0;i<vecToAdd->size;i++){//adds a scalar to each element 
        vecToAdd->svector[i]+=addElement;
        }

        return vecToAdd;
}

**EDIT
Some people asked me which assertion error I got:

Debug Assertion Failed!

Program:
…12\Projects\ConsoleApplication2\Debug\ConsoleApplication2.exe

File:f:\dd\vctools\crt_bld\self_x86\crt\src\dggdel.cpp

Line:52

Expression:_BLOCK_TYPE_IS_VALID(pHead->nBlockUse)

I’ve also made the following changes:
assert(testVec=NULL)
(deAlloc==NULL)

to

assert(testVec==NULL)
(deAlloc==NULL)

this function from:
void dealloc_vec(Vector *deAlloc)

to:

void dealloc_vec(Vector *&deAlloc)

Assertion error fixed, however doesnt produce output. Still working on the debugging.

Also, quite possible this is more C than C++. My prof states in the assignment spec that this is C++, but he switches between the two lots in our class.

Answer 1

assert(testVec=NULL);

will set testVec to NULL and evaluate as equal to that null pointer, which is false when treated as a boolean.

That should almost certainly be assert(testVec == NULL); instead.

For future reference, this is why so-called “Yoda conditions” (NULL == testVec rather than testVec == NULL) are sometimes preferred in C and C++ when comparing to a constant. If you accidentally use = rather than ==, Yoda conditions fail to compile, making the problem more obvious.

With that fixed, you have another problem: dealloc_vec nulls out its local copy of the Vector*, but that’s just a copy of the real pointer; the change doesn’t make it back to the caller. You might want to declare the function to take a Vector*& (a reference to a pointer). Before you do that, though, you have another assignment-instead-of-comparison to fix: if (dealloc=NULL) should be if (dealloc == NULL).

What’s more, the delete[] tempvec; in extend_vec frees memory you’re still using. You’re begging for segfaults and heap corruption if you keep it. So delete it.