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what is the difference between ::std::string and std::string
The former is global? But global for what?Is not namespace std global?
Thanks for helping me.
698
std::string class in C++ C++ has in its definition a way to represent a sequence of characters as an object of the class. This class is called std:: string. String class stores the characters as a sequence of bytes with the functionality of allowing access to the single-byte character.
std::string has a huge number of string-related functions which make it easy to manipulate strings. 2. std::vector, on the other hand, is guaranteed to be contiguous in memory -- that is, &data[x + 1] = &data[x] + sizeof(data[x]). std::string has NO guarantee that it is contiguous in memory.
There are two types of strings commonly used in C++ programming language: Strings that are objects of string class (The Standard C++ Library string class) C-strings (C-style Strings)
Because the declaration of class string is in the namespace std. Thus you either need to always access it via std::string (then you don't need to have using) or do it as you did. Save this answer.
::std::string means string in namespace std in the global namespace. The leading :: forces the lookup to start in the global namespace. Therefore ::std::string always means the string type from the C++ standard library.
std::string means string in namespace std, where std will be looked up in the current scope. Therefore, if there is a class, namespace, or enum named std, name lookup might find that std.
#include <string>
namespace foo {
namespace std {
class string { ... };
namespace bar {
std::string s; // means foo::std::string
::std::string s; // means string from standard library
}
}
}
It is not necessary to use the leading :: as long as you and your collaborators agree to not name anything std. It's just good style.
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