CODEWITHSUNDEEP
c++
Blasco
Blasco

Reputation: 1735

Passing a std::vector as a pointer reference

I have a function that has the following signature and which I cannot change:

bool function(uint8_t*& data, uint32_t size)

I want to pass a std vector, I am able to do it as follows:

std::vector<uint8_t> buffer;
buffer.reserve(10);
buffer.resize(10);

uint8_t* data = &buffer[0];
function(data, buffer.size()))

Is there a way to avoid creating the data pointer? The following doesn't compile:

function(&buffer[0], buffer.size()))

gives a no matching function error.

Upvotes: 5

Views: 1096

Answers (2)

Jabberwocky
Jabberwocky

Reputation: 50778

You probably need this:

uint8_t* data = buffer.data();   // data will point to the first element of the vector
function(data, buffer.size());
// function may have modified the data pointer at this point

Now I would be interesting what exactly function does, especially if it does modify data.

BTW: IMO buffer.reserve(10); is useless as you have a buffer.resize(10); right after anyway.

Upvotes: 2

amc176
amc176

Reputation: 1544

The main problem here is that if function takes a reference to a pointer, it may modify it which would result in unexpected results.

If you are sure the function doesn't modify the pointer itself, you could add an overload to simplify what you want to accomplish:

bool function(uint8_t*& data, uint32_t size) {
    return false;
}

// overloaded on rvalue reference to pointer
bool function(uint8_t*&& data, uint32_t size) { 
    return function(data, size);
}

int main() {
    std::vector<uint8_t> buffer;
    buffer.reserve(10);
    buffer.resize(10);
    function(buffer.data(), buffer.size());
}

Take into account that this is dangerous, especially if function modifies the pointer, so use with caution.

Live demo

Upvotes: 3

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