c ++使用指针访问对象的成员

Question

I have variable mode , which I am declaring with the following line:

StatusRecord mode;

StatusRecord is a struct which holds several variables of different types.

I now want to create a pointer to mode , and populate that pointer with some data by using a function to populate its attributes/ fields. I have tried doing this as follows:

StatusRecord mode;
StatusRecord *modePtr = &mode;
DataStore->getModeData(*modePtr);

Here, I am declaring the struct variable, creating a pointer to it, and populating that pointer using the getModeData() function. However, I now want to use an attribute of the struct ptr I've just populated in a conditional statement:

if(*modePtr->eraseSelect ==2){
    ...
}

But I'm getting a compile error on this line that says:

Error: operand of '*' must be a pointer

Does this mean that the eraseSelect attribute should be a pointer as well as 'modePtr`? How would I fix this error?

Answer 1

Try this:

if(modePtr->eraseSelect ==2){
    ...
}

or this:

if((*modePtr).eraseSelect ==2){
    ...
}

So you can use "dot" syntax to reach fields of an instance or "arrow" syntax to reach fields of a pointer to the instance. In most cases, "arrow" is more suitable.

Answer 2

You dont need to dereference your pointer here:

if(modePtr->eraseSelect ==2){
    ...
}

Answer 3

The issue is at *modePtr->eraseSelect .

The -> is used to access member variables of pointers to objects. So, ptr->someMember is equivalent to *(ptr).someMember . You are mixing up the two, and so it doesn't make sense as you are dereferencing twice.

You should instead use modePtr->eraseSelect instead.