C [heap-use-after-free error] with referencing and push

Below is my code and the execution result.

#include<vector>
#include<algorithm>

typedef struct Block {
    int value;
    Block(int value): value(value) {}
} Block;

int main() {
    std::vector<Block> blocks;
    blocks.emplace_back(1);
    Block& block = blocks[0];
    blocks.emplace_back(2);
    std::max(1, block.value   1);
    return 0;
}

00699 ➤ g   -std=c  11 -fsanitize=address  question.cpp; ./a.out
=================================================================
==32403==ERROR: AddressSanitizer: heap-use-after-free on address 0x000106c00730 at pc 0x0001028fbd90 bp 0x00016d507310 sp 0x00016d507308
READ of size 4 at 0x000106c00730 thread T0
    #0 0x1028fbd8c in main 0x300 (a.out:arm64 0x100003d8c)
    #1 0x1029490f0 in start 0x204 (dyld:arm64e 0x50f0)
....

In my opinion, the combination of reference and emplace_back is wrong.
But why? What happened?

CodePudding user response：

because after emplace new element to blocks, may element's address have change (internal vector expanding operation )-> you save previous address is incorrect. to fix it you just change order of commands.

std::vector<Block> blocks;
blocks.emplace_back(1);
blocks.emplace_back(2);
Block &block = blocks[0];

std::max(1, block.value   1);

show diffence address after each emplace_back

std::vector<Block> blocks;
blocks.emplace_back(1);
Block block = blocks[0]; 
cout << "&blocks[0]" << & blocks[0] << "\n";
blocks.emplace_back(2);
cout << "&blocks[0]" << & blocks[0] << "\n";

std::max(1, blocks[0].value   1);

result:

&blocks[0]0xae1eb0
destructor ,value 1
&blocks[0]0xae2ee0
destructor ,value 1
destructor ,value 1
destructor ,value 2

https://godbolt.org/z/Y9xrv64aq