用make_unique语句重新分配unique_ptr对象-内存泄漏？ [英] Reassign unique_ptr object with make_unique statements - Memory leak?

问题描述

我不明白下面的语句会做什么（特别是第二行）？

I don't get what following statement would do (specially second line)?

auto buff = std::make_unique<int[]>(128);
buff = std::make_unique<int[]>(512);

第二次调用 make_unique 分配运算符将取消分配第一次调用分配的内存，还是会发生内存泄漏？我必须使用 buff.reset（new int [512]）; 吗？

Will the second call to make_unique followed by assignment operator will de-allocate memory allocated by first call, or will there be memory leak? Must I have to use buff.reset(new int[512]); ?

我已经调试了它，但没有找到任何 operator = 被调用，也没有调用任何析构函数（通过 unique_ptr ）。

I've debugged it, but didn't find any operator= being called, nor any destructor be invoked (by unique_ptr).

推荐答案

gcc 5.3：

#include <memory>

extern void emit(int*);

int main()
{
    // declare and initialise buf
    auto buff = std::make_unique<int[]>(128);

    // make_unique on the RHS returns a temporary
    // - therefore an r-value reference

    // therefore this becomes and operator=(unique_ptr&&)
    // (move-assignment)
    buff = std::make_unique<int[]>(512);

    // something to get the compiler to emit code
    emit(buff.get());
}

收益率汇编：

main:
        pushq   %r12
        movl    $512, %edi
        pushq   %rbp
        pushq   %rbx
        call    operator new[](unsigned long)  ; <-- new (1)
        movl    $64, %ecx
        movq    %rax, %rbp
        xorl    %eax, %eax
        movq    %rbp, %rdi
        rep stosq
        movl    $2048, %edi
        call    operator new[](unsigned long) ; <<-- new (2)
        movl    $2048, %edx
        xorl    %esi, %esi
        movq    %rax, %rdi
        movq    %rax, %rbx
        call    memset
        movq    %rbp, %rdi
        call    operator delete[](void*)       ;<-- delete (1)
        movq    %rbx, %rdi
        call    emit(int*)
        movq    %rbx, %rdi
        call    operator delete[](void*)       ;<-- delete (2)
        popq    %rbx
        xorl    %eax, %eax
        popq    %rbp
        popq    %r12
        ret
        movq    %rax, %r12
        movq    %rbp, %rbx
.L3:
        movq    %rbx, %rdi
        vzeroupper
        call    operator delete[](void*)       ;<-- handles a failed assignment
        movq    %r12, %rdi
        call    _Unwind_Resume
        movq    %rax, %r12
        jmp     .L3

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