What is the difference between initializing a string with:
std::string testString = "Test";
and
std::string testString{"Test"};
Is this only syntactic sugar thing or there actually are some performance related differences?
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4 Answers
The {} initialization syntax is known as the uniform initialization syntax, it has a few key differences, but in your code as is they both do the same thing - construct a std::string object from the string literal "Test"
Initializing an object with an assignment is essentially the same as putting the right hand side in parentheses and constructing the object. For example the below two are the same
T obj = a;
T obj(a);
So you should be asking yourself, what is the difference between constructing a string object the following two ways
std::string{"Test"};
std::string("Test");
And the answer is that both the constructions above are the same and call the same constructor for std::string
For more on uniform initialization see https://softwareengineering.stackexchange.com/questions/133688/is-c11-uniform-initialization-a-replacement-for-the-old-style-syntax
1 Comment
caoanan
I'm still confused. Is constructor and copy constructor essentially the same ? How does uniform initialization and initiallizer list work? How's the const char* object ended up with?
There is no difference in this particular case. But try
std::string s1(1, '0'); // calls string(size_type , char )
std::string s2{1, '0'}; // calls string(std::initializer_list<char> )
assert(s1.length() == 1 && s1[0] == '0');
assert(s2.length() == 2 && s2[0] == '\x1');
or with std::vector
std::vector<int> v1(1); // calls vector(size_type )
std::vector<int> v2{1}; // calls vector(std::initializer_list<int> )
assert(v1.size() == 1 && v1[0] == 0);
assert(v2.size() == 1 && v2[0] == 1);
Comments
There is no difference between them.
First declaration is preferred in most projects due to the syntax highlighting.
5 Comments
Curious
What sort of syntax highlighting is missing in the second one?
Blacktempel
@Curious aren't you ;) I think it's more readable. I don't see any missing syntax highlighting either.
Kemal Güler
There is nothing missing @Curious. I just want to say first one is more readable.
xaxxon
your opinion on which is more readable isn't really relevant. Saying that it's preferred in most projects is not even clear that it's your opinion.
Kemal Güler
First declaration is preferred, because it is more readable. That is not my opinion. All my friends use first declaration on their projects. Is it relevant?
I found a clear answer in Herb Sutter
