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wally
wally

Reputation: 11022

Visual Studio and Clang do not throw std::bad_array_new_length

This is a follow up to to a prior question.

In the following program Visual Studio 2015 and Clang both do not throw std::bad_array_new_length. gcc does.

#include <iostream>
#include <random>
#include <exception>
#include <new>

int main()
{
    std::random_device rd;
    std::uniform_int_distribution<int> dist(2,2);
    try {

        auto arr = new int[dist(rd)][4][2]{{{1}},{{2}},{{3}}}; // may write to unallocated memory

        auto val1 = arr[0][0][0];
        auto val2 = arr[1][0][0];
        auto val3 = arr[2][0][0];
        auto result = val1 + val2 + val3;
        std::cout << result;
    }
    catch (std::exception const& e) {
        std::cerr << e.what() << '\n';
    }
    return 0;
}

In Visual Studio the program crashes without any message. In Clang there is no error (perhaps because it avoided the allocation as mentioned in this answer).

Three compilers, three results. Is this undefined behavior or is this is a bug in Visual Studio?

Upvotes: 4

Views: 414

Answers (1)

songyuanyao
songyuanyao

Reputation: 173014

GCC is correct, the behavior is defined by the standard.

$5.3.4/7 New [expr.new]

The expression in a noptr-new-declarator is erroneous if:

...

(7.4) — the new-initializer is a braced-init-list and the number of array elements for which initializers are provided (including the terminating ’\0’ in a string literal (2.13.5)) exceeds the number of elements to initialize.

...

a new-expression with an erroneous expression does not call an allocation function and terminates by throwing an exception of a type that would match a handler (15.3) of type std::bad_array_new_length (18.6.2.2).

Upvotes: 4

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