CODEWITHSUNDEEP
c++vectorsfmlassert
A. D.
A. D.

Reputation: 768

How to make sure the accessed index in a vector exists?

I have a vector of text labels std::vector<sf::Text> texts_. I can create texts and push them into the vector like this:

texts_.push_back(utils::createText(x, y, "SomeString1"));
texts_.push_back(utils::createText(x, y, "SomeString2"));
// etc.

and then easily draw them like this:

for (std::size_t i = 0; i < texts_.size(); ++i) {
  renderTarget.draw(texts_.at(i));
}

I occasionally want to update the texts' strings. What I currently do is:

texts_.at(0).setString("SomeUniqueString1");
texts_.at(1).setString("SomeUniqueString2");
texts_.at(2).setString("SomeUniqueString3");
// ...

All of the above works just fine. Now to the problem:

When updating the strings, what if I accidentally try to access an index of for example 10 even though there are only for example 5 texts in the vector?

If I do that the program will obviously crash. I could check each time if the index is less than the vector's size but that's kind of overkill (I'd have to add a lot more checks to the code...)? How can I without much effort make sure that the text at that index exists in the vector?

Upvotes: 1

Views: 3583

Answers (2)

Mark Ransom
Mark Ransom

Reputation: 308452

If the amount of boilerplate you'd need to write bothers you, just write it once in a function.

template<class T, typename ValueType>
void SafeSetValue(T & container, size_t index, const ValueType & value)
{
    if (index < container.size())
        container[index] = value;
}

SafeSetValue(texts_, 0, "SomeUniqueString1");

You can change the function to do something different in the case of an out-of-bounds index.

Upvotes: 4

justin
justin

Reputation: 104698

If I do that the program will obviously crash. I could check each time if the index is less than the vector's size but that's kind of overkill (I'd have to add a lot more checks to the code...)? How can I without much effort make sure that the text at that index exists in the vector?

If you're accessing the elements using std::vector<>::at(), the check is being performed. If the index is out of range, then an exception will be thrown. Other member functions (notably operator[]) are not checked.

Upvotes: 0

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