strings_are_vectors.md

It is just a string: should I worry?

std::string is a wonderful abstraction, when compared to the awful mess of raw pointers and lengths that you have to deal with in C.

I am kidding, C developers, we love you!

Or we sympathize for you, depends on how you want to look at it.

If you think about it, it should be no more than an std::vector<char> in disguise, with some useful utility that makes sense for text, but no much more.

On one hand, it is, but here comes what is called Small String Optimization (SSO).

Read more about SSO here.

What I want to show you here is that, as any objects that might require memory allocation, you must use best practices you should use with similar containers (even if, arguably, often you need to worry less).

ToString

enum Color{
    BLUE,
    RED,
    YELLOW
};

std::string ToStringBad(Color c)
{
    switch(c) {
    case BLUE:   return "BLUE";
    case RED:    return "RED";
    case YELLOW: return "YELLOW";
    }
}

const std::string& ToStringBetter(Color c)
{
    static const std::string color_name[3] ={"BLUE", "RED", "YELLOW"};
    switch(c) {
    case BLUE:   return color_name[0];
    case RED:    return color_name[1];
    case YELLOW: return color_name[2];
    }
}

This is just an example of how, if you can, you should not create over and over a string. Of course, I can hear you arguing:

"Davide, you are forgetting Return Value Optimization"?

I am not. But a const& is always guaranteed to be the most performing option, so why try your luck?

Reuse temporary strings

Here it comes a similar example in which we potentially recycle the memory already allocated in the past.

You are not guaranteed to be faster with the latter version, but you might be.

// Create a new string every time (even if return value optimization may help)
static std::string ModifyString(const std::string& input)
{
    std::string output = input;
    output.append("... indeed");
    return output;
}
// Reuse an existing string that MAYBE, have the space already reserved
// (or maybe not..)
static void ModifyStringBetter(const std::string& input, std::string& output)
{
    output = input;
    output.append("... indeed");
}

And, as expected...