C++ "pointer being freed was not allocated"

Question

代码很简单，如下：

#include <bitset>
#include <fstream>
#include <iostream>
#include <vector>

using namespace std;

int main() {
    vector<void*> v;

    int a1 = 4;
    string a2 = "123";
    vector<int> a3 = {1, 2, 3, 4};

    int s1 = sizeof a1;
    int s2 = sizeof a2;
    int s3 = sizeof a3;

    v.push_back((void*)(&a1));
    v.push_back((void*)(&a2));
    v.push_back((void*)(&a3));

    fstream _f("test.bin", ios::in | ios::out | ios::binary);
    _f.seekp(0);
    _f.write((char*)(v[0]), s1);
    _f.write((char*)(v[1]), s2);
    _f.write((char*)(v[2]), s3);

    int r1;
    string r2;
    vector<int> r3;

    _f.seekg(0);
    _f.read((char*)(&r1), s1);
    _f.read((char*)(&r2), s2);
    _f.read((char*)(&r3), s3);

    cout << r1 << endl
         << r2 << endl
         << r3[0] << " " << r3[1] << " " << r3[2] << " " << r3[3] << endl;
    _f.close();
}

它的输出如下：

4
123
1 2 3 4
test(51104,0x7fff9c57d3c0) malloc: *** error for object 0x7fe76fd00000:pointer being freed was not allocated
*** set a breakpoint in malloc_error_break to debug

Command terminated

输出很好，但是它说"pointer being freed was not allocated"，但是，我的代码中没有free()操作，我想知道为什么会这样？

但是r2和r3没有同样的问题，下面的代码运行良好。

#include <bitset>
#include <fstream>
#include <iostream>
#include <vector>

using namespace std;

int main() {
    vector<void*> v;

    int a1 = 4;
    string a2 = "123";
    vector<int> a3 = {1, 2, 3, 4};

    int s1 = sizeof a1;
    int s2 = sizeof a2;
    int s3 = sizeof(int)*a3.size();

    v.push_back((void*)(&a1));
    v.push_back((void*)(&a2));
    v.push_back((void*)(&a3));

    fstream _f("test.bin", ios::in | ios::out | ios::binary);
    _f.seekp(0);
    _f.write((char*)(v[0]), s1);
    _f.write((char*)(v[1]), s2);

    int r1;
    string r2;
    vector<int> r3;

    _f.seekg(0);
    _f.read((char*)(&r1), s1);
    _f.read((char*)(&r2), s2);

    cout << r1 << endl
         << r2 << endl;
    _f.close();
    v.clear();
}

输出：

4
123

Answer 1

当您使用以下内容覆盖向量时，您将导致未定义的行为：

_f.read((char*)(&r3), s3);

如果你想要一个指向保存矢量数据的数组的指针，你需要使用r3.data()。而且你不能使用 sizeof r3 来获取它的大小，这是 vector 对象的大小，而不是底层数组。

int s3 = r3.size() * sizeof(int);
_f.read((char*)r3.data(), s3);

见How to get std::vector pointer to the raw data?

C++ "pointer being freed was not allocated"

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