8

Normally, I would return a std::string from a function because returning a const char* would require the caller to provide an output memory buffer, and that buffer is not resizable.

But is returning a const char* valid if its from a string literal?

const char* generate_c_string() {
    return "ABC";
}

Doing in this way (if valid) would likely be faster as I would not need to dynamically allocate memory to construct a std::string.

It probably is valid, because const char* x = "ABC"; is valid. Is there a reference from the C++ standard that substantiates its validity?

Bernard
  • 5,209
  • 1
  • 34
  • 64
  • I don’t understand why the caller would require to provide any buffer if you return a pointer. – Sami Kuhmonen Dec 20 '17 at 05:15
  • Despite voting to close as a duplicate, I upvoted question and answer because both are still useful – Tas Dec 20 '17 at 05:16
  • 2
    Note that for such short strings the most common std::string implementations do not allocate any dynamic memory. [Meaning of the acronym SSO in the context of std::string](https://stackoverflow.com/questions/10315041/meaning-of-acronym-sso-in-the-context-of-stdstring) – Bo Persson Dec 20 '17 at 05:31
  • It's quite possible that a `std::string_view` suffices if you don't need a full `std::string`. Of course it still has the same lifetime requirements since it doesn't use its own storage. – chris Dec 20 '17 at 05:36
  • @Sami If the function wasn't as simple as returning a static string (perhaps we need to concatenate some text), then the caller should pass a output `char*` argument to the function. – Bernard Dec 20 '17 at 08:54
  • Oh, yes, as an argument, but then one wouldn’t return a pointer. That’s what baffled me. – Sami Kuhmonen Dec 20 '17 at 09:03
  • @Sami Sorry, I wasn't clear about that in the question. But wouldn't I still need to return a pointer to the past-the-end character? – Bernard Dec 20 '17 at 09:09

1 Answers1

12

This is valid, for string literals,

String literals have static storage duration, and thus exist in memory for the life of the program.

The pointer returned would remain valid in the life of the program.

songyuanyao
  • 169,198
  • 16
  • 310
  • 405