SyntaxFix

[c++] What is the use of "using namespace std"?

  • using: You are going to use it.
  • namespace: To use what? A namespace.
  • std: The std namespace (where features of the C++ Standard Library, such as string or vector, are declared).

After you write this instruction, if the compiler sees string it will know that you may be referring to std::string, and if it sees vector, it will know that you may be referring to std::vector. (Provided that you have included in your compilation unit the header files where they are defined, of course.)

If you don't write it, when the compiler sees string or vector it will not know what you are refering to. You will need to explicitly tell it std::string or std::vector, and if you don't, you will get a compile error.

Examples related to c++

• Method Call Chaining; returning a pointer vs a reference? • How can I tell if an algorithm is efficient? • Difference between opening a file in binary vs text • How can compare-and-swap be used for a wait-free mutual exclusion for any shared data structure? • Install Qt on Ubuntu • #include errors detected in vscode • Cannot open include file: 'stdio.h' - Visual Studio Community 2017 - C++ Error • How to fix the error "Windows SDK version 8.1" was not found? • Visual Studio 2017 errors on standard headers • How do I check if a Key is pressed on C++

Examples related to namespaces

• Class 'App\Http\Controllers\DB' not found and I also cannot use a new Model • How do I get an object's unqualified (short) class name? • socket.error:[errno 99] cannot assign requested address and namespace in python • What is the use of "using namespace std"? • Visibility of global variables in imported modules • Using :: in C++ • 'namespace' but is used like a 'type' • type object 'datetime.datetime' has no attribute 'datetime' • Why am I getting error CS0246: The type or namespace name could not be found? • string in namespace std does not name a type

Examples related to std

• Converting std::__cxx11::string to std::string • What is the use of "using namespace std"? • How to get error message when ifstream open fails • How to declare std::unique_ptr and what is the use of it? • declaring a priority_queue in c++ with a custom comparator • cc1plus: error: unrecognized command line option "-std=c++11" with g++ • How to convert std::chrono::time_point to calendar datetime string with fractional seconds? • string in namespace std does not name a type • cout is not a member of std • printf with std::string?

Examples related to using

• What is the use of "using namespace std"? • Do HttpClient and HttpClientHandler have to be disposed between requests? • MySQL JOIN ON vs USING? • in a "using" block is a SqlConnection closed on return or exception? • Should I Dispose() DataSet and DataTable? • What is the best workaround for the WCF client `using` block issue? • What is the C# Using block and why should I use it? • What are the uses of "using" in C#?