C + + standard 14 cancels decltype the return type of the derived function

Table of Contents

• 1. Auto keyword not supported before c++11
• 2. c++11 Support Auto keyword
  • 2.1. But the function return type cannot be inferred automatically
  • 2.2. Use Decltype to declare the return type
• 3. c++14 let things go back to the simple
• 4. Which C + + version should we use

1 Auto keyword not supported before c++11

The following code is not supported in c++11

Auto Add (int a, int b) {   int i = a + b;   return i;} int main (int argc,char * * argv) {  try {     std::cout << Add (+) << Std::endl;   } catch (Std::exceptio N Const &e) {     std::cerr << e.what () << Std::endl;  }}

The compiler clang++ 3.6 will error as follows:

.. /src/main.cc:13:1: Warning: ' auto ' type specifier is a c++11 extension [-wc++11-extensions]auto Add (int a, int b) {^ ... /src/main.cc:13:1: Error: ' Auto ' not allowed in function return Typeauto add (int a, int b) {^~~~

2 C++11 Support Auto keyword2.1 However, the function return type cannot be inferred automatically

Or the above example code, this compilation plus-std=c++11

.. /src/main.cc:13:1: Error: ' Auto ' return without trailing return type; deduced return types is a c++14 extensionauto add (int a, int b) {^1 error generated.

Here clang++ an error, saying that auto does not follow the description of the return type, or use the deduced return types provided by the C++14 standard.

2.2 Declaring return types using Decltype

Let's take a look at C++11 's recommended practice, and add a weird syntax to the back of the function.

Auto Add (int a, int b), decltype (A + b) {

Compiled by.

3 C++14 let things go back to the simple

Decltype (A + B) This syntax makes people feel less like C + +. But the 14 standard as a 11 standard quick follow-up, and pull things back. Decltype became a short-lived transition program. Now it can be completely abandoned. After adding-std=c++14 in the compile option, the following code passes the

Auto Add (int a, int b) {   int i = a + b;   return i;}

4 which C + + version should we use

Since the C++14 standard has been released, and the main compilers are already supported, so now is not the time to talk about c++11, but should directly use the C++14 standard. Here is the clang compiler support for the C + + standard document at the same time, here is my example project: [Email protected]:newlisp/cppwizard.git, using my own newLISP builder for C + + Compiling the code requires only modifying the compilation options of the Debug_config.lsp file.

(Set ' Compile-options "-g-std=c++14")

Updated C + + 17 or 1z is still in the process of standard-setting and is not currently recommended.

Author:dean

Created:2015-12-27 Day 10:23

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C + + standard 14 cancels decltype the return type of the derived function