std::nothrow(3)

💅 std::nothrow(3) — C++ Standard Library

okay so bestie, real talk: this is the std::nothrow page from the C++ Standard Library, and it's honestly shorter than my attention span but it's iconic in its own lowkey way. let's get into it 🫶

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✨ NAME ✨

std::nothrow — literally just std::nothrow. that's the name. she's self-titled, main character energy, no notes 💅

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🌸 SYNOPSIS 🌸

first things first: this whole situation lives in the header <new>. don't forget to include it or nothing works and you'll be sad 😭

here's the actual declaration, verbatim, no cap:

struct nothrow_t {};

(until C++11)

struct nothrow_t { explicit nothrow_t() = default; }; (1)

(since C++11)

extern const std::nothrow_t nothrow; (2)

so what's the tea? std::nothrow_t is an empty class type — yes, empty, she's minimal, she's chic ✨ — and her whole job is to disambiguate the overloads of throwing and non-throwing allocation functions. like, she's the little name tag that tells the compiler which new you meant. and std::nothrow is a constant of it. a whole const object. living her truth. 👑

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🦋 EXAMPLE 🦋

bestie run this code, it's giving educational AND dramatic:

// Run this code

#include <iostream>
#include <new>

int main()
{
    try
    {
        while (true)
        {
            new int[100000000ul];   // throwing overload
        }
    }
    catch (const std::bad_alloc& e)
    {
        std::cout << e.what() << '\n';
    }

    while (true)
    {
        int* p = new(std::nothrow) int[100000000ul]; // non-throwing overload
        if (p == nullptr)
        {
            std::cout << "Allocation returned nullptr\n";
            break;
        }
    }
}

the vibe check here: the first loop is the throwing overload, so when the memory runs out it yeets a std::bad_alloc at you and you catch it. the second loop is the non-throwing overload — it doesn't scream, it just quietly hands you nullptr and you check for it like a responsible adult 🧚

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⭐ OUTPUT ⭐

std::bad_alloc
Allocation returned nullptr

see? one of them yelled, one of them just sighed. both valid. 💀

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🔥 DEFECT REPORTS 🔥

okay so the committee had to retroactively fix stuff — these behavior-changing defect reports got applied to already-published C++ standards. history being rewritten in real time, we love to see it 🙈

• DR: LWG 2510
• Applied to: C++11
• Behavior as published: the default constructor was non-explicit, which could lead to ambiguity
• Correct behavior: made explicit

so yeah, the default constructor got promoted to explicit because ambiguity is not the vibe. periodt. 💅

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🌈 SEE ALSO 🌈

• operator new — allocation functions
• operator new[] (function)

go read those next, i believe in you 🫶✨

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that's the whole page, bestie — short, sweet, and fully documented. slay. 💖

source: http://cppreference.com · version/date: 2024.06.10 · page: std::nothrow(3) — mwah, drink some water, go touch grass, and may all your allocations return exactly what you expected 🎀🦋