为什么我的代码出现“访问冲突读取位置”错误？

Question

Can anyone tell me why I get "Access violation reading location " with this code example? And how can i fix this?

#include <vector>
using namespace std;
struct StructTest;
struct Struct1;
typedef struct Struct1{
    StructTest* test;
} Struct1;

typedef struct StructTest{
    vector<Struct1*> test123;
} StructTest;

static StructTest* abc;

int test(){
    abc = (StructTest*) malloc(sizeof(StructTest));;
    Struct1* a1 = (Struct1*) malloc(sizeof(Struct1));
    a1->test = abc;
    abc->test123.push_back(a1);
    return 0;
}

int main(){
    test();
    return 0;
}

Answer 1

You didn't create test123 . Allocate the structs with new rather than malloc and this will create test123 for you.

abc = new StructTest;
Struct1* a1 = new Struct1;

Remember to dispose with delete rather than free .

In fact, since you are using C++ you should simply stop using malloc .

Answer 2

It's crashing on this line:

abc->test123.push_back(a1);

The reason is because you allocate it two lines above using malloc . Therefore, the contents of test123 are uninitialized. So it crashes when you call push_back on it.

Answer 3

Do not use malloc, use new. malloc does not cause constructors be called so in this case your vector is not a valid object.

Answer 4

Because, when you allocate a block with "malloc" it may contain garbage, zeros, or whatever.

The object test123 is a C++ object, whose constructor has not been executed. Try using operator new instead.

Also, while we're on the subject, in C++, there is no need to typedef structs, they will become first-class names automatically.