C++ Map class emplace example

C++ > Map class > Emplace

Inserts an element constructed in place into a map.

Example 

// ConsoleApplication1.cpp : Defines the entry point for the console application.

//

#include "stdafx.h"

#include <map>

#include <string>

#include <iostream>

using std::endl;

using std::cout;

using std::cin;

int _tmain(int argc, _TCHAR* argv[])

{

       std::map <int, std::string> map;

       auto ret1 = map.emplace(1, "one");

       auto ret2 = map.emplace(2, "two");

       auto tree1 = *ret1.first;

       auto tree2 = *ret2.first;

       cout << "First element is (" << tree1.first << ", " << tree1.second << ")" << endl;

       cout << "Second element is (" << tree2.first << ", " << tree2.second << ")" << endl;

       int ret;

       cin >> ret;

       return ret;

}

#pragma once C# example

C++ > Pragma directives > #pragma once

Specifies that the file will be included only once by the compiler when compiling a source code file, so the build times is reduced.

Example:

HeaderClass.h

#pragma once

// Code placed here is included only once 

namespace Application{

class HeaderClass

{

public:

    HeaderClass();

};

} // namespace Application

Cout Cin C++ Example

C++ > iostream > cout, cin

Example

# include "stdafx.h"

# include <iostream>

using  namespace std;

int _tmain(int argc, _TCHAR* argv[])

{

       int number;

       cout << "Please enter a number: ";

       cin >> number;

       cout << "The number you entered is " << number;

       cin >> number;

       return 0;

}

C++ Preprocessor

C++ > Preprocessor 

Preprocessor performs preliminary operations on C++ files before they are passed to the compiler. 

• insert files
• compiler error messages
• conditionally compile code 

The preprocessor is a text processor that manipulates the text of a source file as part of the first phase of translation. The compiler ordinarily invokes the preprocessor in its first pass, but the preprocessor can also be invoked separately to process text without compiling.