CODEWITHSUNDEEP
c++exceptionmemory-managementvector
Denys S.
Denys S.

Reputation: 6525

bad_alloc while initializing and filling a vector?

While trying to generate a vector of random numbers I stumble across a std::bad_alloc error. Here's my code:

#include "search.h"
#include "gtest/gtest.h"

int _size = 100;

std::vector<int> GetSortedVector(int size){
    //init vector
    std::vector<int> v(size);
    //fill with random numbers
    for (std::vector<int>::size_type i=0; i < v.size(); i++)
        v.push_back( std::rand()%(2*size) );
    //return the setup vector
    return v;
}

//triggered automatically
TEST(BinarySearch, NonUniqueSorted){
    std::vector<int> v = GetSortedVector(_size);//nothing moves farther than this line
}

P.S.: I do use generate() by now, but am still curious why it failed.

Upvotes: 5

Views: 1892

Answers (2)

Luchian Grigore
Luchian Grigore

Reputation: 258618

v.push_back increases the size, so i<v.size() is never false.

Since your vector is already size in length, you need to fill it with

for (std::vector<int>::size_type i=0; i < v.size(); i++)
    v[i] = std::rand()%(2*size);

or use reserve instead:

std::vector<int> v;
v.reserve(size);

keep the push_back and check against size. I won't suggest std::generate because you said you're already doing it like that.

Upvotes: 8

user405725
user405725

Reputation:

Zoom into the following part:

for (std::vector<int>::size_type i=0; i < v.size(); i++)
        v.push_back( std::rand()%(2*size) );

Every time you call push_back(), vector's size is increased by 1. Therefore, i < v.size() will never evaluate to false and your loop will go on until you run out of memory. One of the possible ways to fix it is to capture size() once, for example:

for (std::vector<int>::size_type i=0, s = v.size(); i < s; i++)
        v.push_back( std::rand()%(2*size) );

Upvotes: 2

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