Why is this so much slower in C++?

Question

I have converted this simple method from C# to C++. It reads a path table and populates a list of lists of ints (or a vector of vectors of ints).

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Answer 1

I'm not exactly sure what is going on here, but I see a few ways in which you can optimize your code. If this doesn't get you there, then there might be something else going on.

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How big are your strings? As you are passing them in your C++ version, you are making copies because you are "passing by value". Try passing it by constant reference:

void Level::PopulatePathVectors(const string &pathTable)

This passes the object by reference, meaning it is not making a copy. Then, it is customary to make it const to ensure that it is not getting modified in your function.

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Use .append or += to extend tempString. I believe you are making a new string object, then replacing the old one with just +, while += and .append are going to modify the current one in place:

tempString.append(line[count]);

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You can also tweak out a bit more performance by declaring your variables at the top and then reassigning into them. This will prevent them from getting recreated every time. For example, put string line; before your for-loop, because it's going to get overwritten anyways.

There are a few places you can do this, such as with tempString.