String fundamentals

Question

So far I know the following ways to have strings in C++ (although some of these are from C)

string string1 = "Hello"; char string2[] = "Hello"; char string3[] = {'H', 'e', 'l', 'l', 'o', 0}; const char *string4 = "Hello";

I find the first method to be the most convenient as it supports several methods and has overloaded operators. But I believe that also makes it the least optimized in terms of performance, is that so?
Which method is the best in terms of performance / speed?
Which of these are allocated on stack and which on heap? I mean I don't see any new keyword, but then my intuition says otherwise.

Computers are very fast. Convenience is underrated, efficiency is overrated, especially by beginners. The asnwer to question three is stack (probably), stack, stack, neither. — john
– john, Commented Aug 2, 2020 at 11:31
The explanation of the 'probably' answer is that most string implementations use short string optimization which means that short strings get allocated on the stack. If the string was large then it would be heap allocated. — john
– john, Commented Aug 2, 2020 at 11:34
1. That is incorrect. 2. For what purpose? Just sitting there, or doing something with it? 3. Maybe stack maybe heap; stack (if in context of a function); stack (string3 is exactly the same as string2); the pointer is stack, the data pointed to is neither stack nor heap. — Eljay
– Eljay, Commented Aug 2, 2020 at 11:34
std::string is dynamic so it will probably save the string on the heap — Roy Avidan
– Roy Avidan, Commented Aug 2, 2020 at 11:41
alright, so I'm assuming performance won't be much different and so using the first method is best (most of the times at least). Although I'm not sure I got whatever you guys told about string4 — Eeshaan
– Eeshaan, Commented Aug 2, 2020 at 11:50

Waqar · Accepted Answer · 2020-08-02 11:51:09Z

I find the first method to be the most convenient as it supports several methods and has overloaded operators.

Correct. And it should be the default way you should handle strings in C++.

But I believe that also makes it the least optimized in terms of performance, is that so?

Least optimized? For what? As far as a normal application is concerned, std::string is very fast. It is heavily optimized for many many use cases. A large number of very smart people work very hard to make sure it is fast. Take a look at this SO question where someone tries to implement one of the std::string operations themselves but is unable to beat std::string performance.

Which method is the best in terms of performance / speed?

std::string is the fastest. Before you say it's not, think how you are going to use your strings. Are you doing any of the following?

Comparing
Concatenation
Passing strings around in functions
searching

std::string can do all these very quickly. However, if you end up using const char* or the char array, you will have to do these operations manually which will almost certainly be slower than the std::string implementation. Not to mention the various pointer and memory issues you will have to tackle.

Which of these are allocated on stack and which on heap? I mean I don't see any new keyword, but then my intuition says otherwise.

All of the strings you showed are on stack, even std::string. std::string has SSO(short string optimization) built-in which stores short strings on the stack.

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