Evgenij LegotskojMay 7, 2017, 4:51 a.m.

C++ - Tutorial 001. Hello World

The minimum program in C ++ is

int main() { } // the minimal C++ program

In this program, the declaration of the main function is presented, which takes no arguments. The curly brackets reflect grouping in C++ and in this case show the body of the main function. That is, the beginning of the main function is the opening parenthesis, and the end of the main function is the closing parenthesis. A double slash shows the beginning of the comment. Comments are ignored by the compiler and serve to refine the information in the code.

Each program written in C++ has the function main() , with which the program starts. The main() function, as a rule, returns the result of its execution, which is indicated by the int (integer) data type written before the main() function. If the function is successful, the main() function returns 0 as the result. The value of the result, other than zero, signals an abnormal termination of the program.

The value returned by the program upon completion can be used in the operating system for service purposes.

A typical example of the first program in any programming language is the output of the text "Hello, World!" :

#include <iostream>

int main()
{
    std::cout << "Hello, World!\n";
}

But is it so simple in this program? In general, already this one small program carries a very large layer of information, which must be understood for development in C++.

  1. #include directive
    #include <iostream>
    tells the compiler that it is necessary to connect a header file, the components of which are planned to be used in the file where the main() function is declared. iostream is a standard input library from STL. That is, the functional of libraries is already used here, although it is the standard for the language. And the last point is the angle brackets, in which the name of the library is located, which say that this is the inclusion of external files in the project, and not those that are part of the project. The same files that are included in the project are connected by enclosing them in normal quotes, for example #include "myclass.h" . This library connection is standard. For example, in Visual Studio , if this standard is not followed, errors will occur.
  2. std is the use of the namespace in which the cout output statement is located. Namespaces were introduced in C ++ in order to remove name conflicts between libraries and the developer's project, if there are repeated names of functions or classes somewhere. In Java, the package system is used to resolve name conflicts.

  3. cout is an output operator that has an overloaded operator << , in order not to use a separate function to output text to the console.

This is in addition to the fact that the record of the main function can have a different form, although the standard is two records:

  1. int main()
  2. int main(int argc, char* argv[])

You can find more records like void main() , etc. But these are erroneous records, although in some compilers they will be compiled, even without errors and warnings.

In the record int main (int argc, char * argv []) arguments are passed:

  1. argc - indicates the number of arguments passed. Always at least 1, because the name of the program is always passed
  2. argv[] - an array of pointers to arguments that are passed as string variables.

If argc is greater than 1, then additional arguments were passed when the program was started.

The check can look like this:

#include <iostream>
 
int main(int argc, char* argv[])
{
    // If an additional argument is passed,
    if (argc > 1)
    {
        // Then try to derive the argument
        std::cout << argv[1]<<endl;
    } 
    else
    {
        // Otherwise, we inform you that the arguments were not transmitted
        cout << "Without arguments" << endl;
    }
    return 0;
}

In general, there are a lot of things that you need to understand in C ++, even for a small program, but this is only more interesting ;-)

We recommend hosting TIMEWEB
We recommend hosting TIMEWEB
Stable hosting, on which the social network EVILEG is located. For projects on Django we recommend VDS hosting.
Support the author Donate
s

Забыли std
std::cout << argv[1]<< std:: endl; //строка 9
std:: cout << "Without arguments" << std:: endl; //строка 14

Comments

Only authorized users can post comments.
Please, Log in or Sign up
Timeweb

Let me recommend you the excellent hosting on which EVILEG is located.

For many years, Timeweb has been proving his stability.

For projects on Django I recommend VDS hosting

View Hosting
C

C++ - Test 005. Structures and Classes

  • Result:75points,
  • Rating points2
AE

C++ - Test 005. Structures and Classes

  • Result:25points,
  • Rating points-10
m

C++ - Тест 003. Условия и циклы

  • Result:28points,
  • Rating points-10
Last comments
AB

Qt/C++ - Lesson 008. QDataWidgetMapper - Working with the database via a widget

Понял сам так - происходит через setTable() "Sets the database table on which the model operates to tableName. Does not select data from the table, but fetches its field information", а затем че…
AB

Qt/C++ - Lesson 008. QDataWidgetMapper - Working with the database via a widget

Начал делать что-то похожее, но без sql. Не очень понимаю, что делает mapper->setCurrentModelIndex(model->index(row,0)); Вернее не понимаю вот что: откуда он берёт данные, кот…
IV

Qt/C++ - Lesson 048. QThread — How to work with threads using moveToThread

Не получается сделать connect, получаю гору ошибок. В чем может быть дело ?
IV

Qt/C++ - Lesson 034. Echo Server based on QTcpServer

Добрый день, разрешите вопрос: во всех примерах работы с QTcpServer его всегда создают в main.cpp, нет ли возможности корректно сохдать его в MainWindow.cpp ? Просто если перенести код…
D

Django - Tutorial 001. Deploying a site on Django + PostgreSQL + Gunicorn + Nginx

А почему нельзя? Где можно об этом почитать? Киньте, пожалуйста, в меня ссылкой.
Now discuss on the forum

Отправка картинки в DRF

Да я знаю ;-) используйте, пожалуйста, в следующий раз средства сайта. В данном случае сторонний сервис ни к месту.
  • BlinCT
  • April 9, 2021, 8:15 a.m.

Работа с созданным обьектом qml через Qt.createComponent

Добрый день. И как это решает мою проблему?) Item{ id: root property var model property bool headers : false property string objectName property int iMaxWidthRow:…

Проект на cmake и QCharts

Кто-нибудь сталкивался с проблемой скроллинша чарта ? если допустим увеличить в ширину сам чарт, как скроолить весь чарт а не только его видимую часть ?

Ожидание ввода QLineEdit

Попробовал, крешится напрочь... Такое чуство что таймер не удаляется.... и к нему снова идет обращение....

QScrollArea dynamically add QCheckBoxes

Всё правильно. Это просто спамер, который отправился в вечный бан.
About
Services
© EVILEG 2015-2020
Recommend hosting TIMEWEB