CODEWITHSUNDEEP
c++vectorstruct
Josh
Josh

Reputation: 6282

Vector of structs with dynamically allocated members

If I wanted to fill a vector with a struct, and in the struct I need to dynamically allocate/relocate the WCHAR arrays, how would I populate this?
I can't use std::wstring because I'm going to be using the members with the Windows API. And functions like RegQueryValueEx require a LPBYTE to receive the data.

Or is there some other STL container I should be using?

Example Code:

typedef struct {
    WCHAR *str1;
    WCHAR *str2;
    DWORD SomeOtherStuff;
} MYSTRUCT;

vector<MYSTRUCT> myvector;

Upvotes: 1

Views: 1481

Answers (2)

Mike Seymour
Mike Seymour

Reputation: 254751

Use std::vector<WCHAR> for the structure members. This will give your structure the necessary copy/move semantics to put it in a vector and, when you need a raw pointer for some API, it's avaiable as &str1[0].

Remember to make sure it's large enough (either by initialising it to the required size, or calling resize()) before doing anything that will access the data. Also remember that pointers and iterators to the data will become invalid when the vector is resized.

Upvotes: 2

Tim
Tim

Reputation: 9172

You could define a copy constructor, assignment operator, and destructor for your struct. And then all the copies made of each instance would have their own copy of the dynamically allocated memory.

Or you could just use std::wstring

std::wstring provides an accessor method c_str, which gives you a pointer to the underlying null-terminated string. This lets you use std::wstring with C APIs.

std::wstring wide_string;
some_win_api_call( wide_string.c_str() );  // sending a string to winapi

To get a string from the winapi, you need to allocate a buffer yourself, and pass in a pointer to the buffer, along with the length of the buffer.

wide_string.reserve( 256 );  // allocate some space to receive a string
get_string_from_winapi( &wide_string[0], wide_string.capacity() );

You might need to do wide_string.capacity() * sizeof(wchar_t) if the api wants the length in bytes. My example assumes length in characters.

Upvotes: 0

Related Questions