C++: terminate called after throwing an instance of 'std::bad_alloc' — what(): std::bad_alloc

Meaning

A bad_alloc is thrown by operator new when allocation fails. Many cases are not a real shortage: an int size that became huge after a signed/unsigned conversion, an uninitialised variable passed to std::vector(n), or an infinite loop adding elements. Also check limits like ulimit -v, container memory limits, and 32-bit address space.

Common causes

• Size computed from an uninitialised or negative number (converted to a huge size_t)
• Real memory exhaustion: unbounded growth, leaks
• Container or ulimit -v memory limit (Docker, cgroups)
• 32-bit build hitting the 2–4 GB address-space limit
• new of an enormous array

Detailed fix by platform

Code examples

#include <vector>
#include <new>
#include <iostream>

int main(int argc, char** argv) {
    long long n = argc > 1 ? std::atoll(argv[1]) : -1;     // -1 becomes a huge size_t below
    if (n < 0 || n > 100'000'000) { std::cerr << "bad size\n"; return 1; }
    try {
        std::vector<int> v(static_cast<std::size_t>(n));
    } catch (const std::bad_alloc& e) {
        std::cerr << "out of memory: " << e.what() << "\n";
    }
}

How to diagnose

1. Size — What size was requested?
2. Memory — Free memory and limits?
3. Growth — Does memory keep growing (leak)?

More related errors