Is optimizing small std::strings wiht c-style functions often pointless?-CodePudding

Let's say we've got the following piece of code and we've decided to optimise it a bit:

/// BM_NormalString
bool value = false;       
std::string str;
str = "orthogonal";
if (str == "orthogonal") {
    value = true;
}

So far we've come up with two pretty simple and straightforward strategies:

/// BM_charString
bool value = false;
char *str = new char[11];
std::strcpy(str, "orthogonal");
if (std::strcmp(str, "orthogonal") == 0) {
    value = true;
}
delete[] str;

/// BM_charStringMalloc
bool value = false;
char *str = (char *) std::malloc(11);
std::strcpy(str, "orthogonal");
if (std::strcmp(str, "orthogonal") == 0) {
    value = true;
}
free(str);

If we try and benchmark our three approaches we, quite surprisingly, won't see much of a difference. Although bench-marking it locally gives me even more surprisingly disconcerting results:

|      Benchmark       |     Time         |    CPU    |    Iterations |
|----------------------|------------------|-----------|---------------|
|    BM_charString     |     52.1 ns      |  51.6 ns  |    11200000   |
| BM_charStringMalloc  |     47.4 ns      |  47.5 ns  |    15448276   | 
|  **BM_NormalString** |     17.1 ns      |  16.9 ns  |    40727273   |

Would you say then, that for such rather small strings there's almost no point in going 'bare metal' style (by using C-style string functions)?

CodePudding user response：

For small strings, there's no point using dynamic storage. The allocation itself is slower than the comparison. Standard library implementers know this and have optimised std::basic_string to not use dynamic storage with small strings.

Using C-strings is not an "optimisation".