Clear c что это
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Clear c что это

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Clear c что это

It is one of the basic need a program may required i.e clear the console during execution time.

Need of a clear console screen :

A console screen must be cleared once its stated objectives have been completed. A user also needs a clear screen for new data. Like any other language, C offers a variety of ways to clear the console screen.

The clear screen method or function not only depends on types of operating systems but also compilers, which include modern as well as older compilers

There is function named clrscr() which is included in conio.h and is a nonstandard function and is present in conio.h header file which is mostly used by MS-DOS compilers like Turbo C. It is not part of the C standard library or ISO C, nor is it defined by POSIX.
So what should we use there?
There are two more ways to clear console:

  1. By Using system(“clear”)
  2. By using a regex “\e[1;1H\e[2J”
  3. by using clrscr() function
  4. System(“cls”)

The following are some of the factors that influence a console’s clear screen:

  1. Type of operating system.
  2. User compiler new or old.
  3. Need of the user.

Prerequisites :

  1. Some clear screen methods are platform specific. They won’t run on other systems or compilers.
  2. If you are using a visual studio then prefer the system.(“cls”)


clrscr() is an abbreviation of the clear screen. It aims to clear the console screen. clrscr() is a library function located in the console input output header file <conio.h>. The previous screen on the console is cleared whenever the clrscr () is invoked in a program. To call the clrscr() function, it must define inside any function or the main function.

Properties :
  1. Window Specific
  2. Supported by older compiler
  3. Doesn’t allocate extra resource.



Return :

Example :

let’s take an example that will display the addition of two numbers using clrscr().

what does clear() do?

if I don’t have istring.clear.() in my code, the output would be «nan%». everything works well and output is 60% if it’s there. What does it really do there? why it makes a difference? (p.s my input is «y n y n y»)

1 Answer 1

clear() resets the error flags on a stream (as you can read in the documentation). If you use formatted extraction, then the error flag «fail» will be set if an extraction fails (e.g. if you’re trying to read an integer and there isn’t anything parsable). So if you’re using the error state to terminate the loop, you have to make the stream usable again before going into the next loop.

In your particular case, though, your code is just poorly written and violates the «maximum locality principle». A saner version, that as a bonus doesn’t require clear() , would be like this:

Some people would even write the outer loop as for (std::string temp; std::getline(readfile, temp); ) < /* . */ >, though others consider this abuse.

Удалить векторное содержимое и освободить память в C++

В этом посте мы обсудим, как удалить содержимое вектора и освободить память, выделенную вектором, для хранения объектов в C++.

1. Использование vector::clear функция

Мы можем использовать vector::clear функция для удаления всех элементов из вектора. Он работает, вызывая деструктор для каждого векторного объекта, но основное хранилище не освобождается. Итак, у нас остался vector нулевого размера, но с некоторой конечной емкостью.


The vector size is 0, and its capacity is 5

Начиная с C++11, мы можем вызывать vector::shrink_to_fit функционировать после clear() , что уменьшает способность вектора увеличивать размер. Он работает, “запрашивая” перераспределение вектора.


The vector size is 0, and its capacity is 0

2. Использование vector::erase функция

Другим решением является вызов vector::erase функцию на векторе, как показано ниже. Это также страдает от той же проблемы, что и clear() функция, т. е. не гарантируется перераспределение памяти в векторе.


The vector size is 0, and its capacity is 0

3. Использование vector::resize функция

Мы также можем использовать vector::resize функция изменения размера вектора. Обратите внимание, что эта функция не уничтожает векторные объекты, и все ссылки на объекты остаются действительными.



The vector size is 0, and its capacity is 0

4. Использование vector::swap функция

Все вышеперечисленные решения не могут освободить память, выделенную для векторного объекта, без вызова метода vector::shrink_to_fit функция. shrink_to_fit() уменьшает емкость, чтобы соответствовать размеру, но мы не можем полностью полагаться на это. Это связано с тем, что он делает необязательный запрос, и реализация вектора может полностью его игнорировать.

Существует еще один обходной путь для освобождения памяти, занятой векторным объектом. Идея состоит в том, чтобы заменить vector пустым вектором (без выделенной памяти). Это освободит память, занимаемую вектором, и всегда гарантированно будет работать.

Clear Console in C

During the execution of the program, the developer needs to clear the screen or remove the previous output for new output. To clear the console screen in the c language many methods are available.

Here are some of the following :

  1. Clrscr() function
  2. System(“clear”) function
  3. System(“cls”) function
Important Note :

This function depends on the type of operating system, compiler, and other factors.
For example: If you try to compile the program using the clrscr() function in a modern compiler then it will generate an error. These errors are "Function is not declared " or "conio. h file not found " etc.
So it is recommended that use this function in their specified compiler.

1 .clrscr () function:

Clrscr() is a library function in the c language. It is used to clear the console screen. It moves the cursor to the upper left hand of the console. Clrscr() function is used with conio.h header file.

It clears the console screen whenever a function invokes. To use this function Users can call clrscr() in the main function or any function in which it is defined.

Clrscr() is not a standard library is predefined function in conio.h [console input output header file ] header file . So it is only used to clear consoles in old compilers like Turbo C or C++.

  1. Make execution fast.
  2. Useful in MS-DOS console screen in the older compiler.
  1. Not useful for modern compilers.
  2. Only available in the window system.
  3. This function is optional.
  4. Only work for turbo c compiler.
  5. Every time user must include a conio.h file.

Void clrscr (void);
Parameter :
Void: it is a function that has no return data type.
clrscr() : function to clear screen
Return Type :
Don’t have any return type .as it uses the void function.



Explanation :

In this program, we calculate and print the sum of two numbers. after the declaration of two numbers, we have to call the clrscr() function. I will clear previous output screen .When we execute this program for first time it will print the sum of number and when we run this program for second time it will clear the previous output and only display current output .
If we don’t use clrscr() then it prints new output along with old this

This will not work on Dec C++ Complier . Use cleardevice() function.


The second method to clear console screen is clear() in linux.
As the name suggests it is used to clear the console screen. In which system() is a library function that is available in stdlib.h header file.


System: the system used to run command prompt commands
Cls: clear the output screen or console screen.

Advantage :
  1. Useful for the Linux and macOS operating systems.
  2. Useful for modern compilers like GCC/gcc++ in Linux.
  1. limited to specific operating system or complier.
  2. Only useful for Linux.

Example :


After Clear The Ouput

Explanation :

In the given program we have used the system("clear") function to clear the screen . in the first step it prints “ Hello “ and the getch will wait to accept a character and doesn’t echo it on the screen.
Then system(“clear”) will clear the previous output and print the next statement World on the console.


Cls() function is used to clear the console screen like clrscr(). Where system() is a library function available inside stdlib.h [ standard library library] header file.


System: used to run command prompt commands and also wait for a user to enter or press the key to terminate the program.
Cls: clear the output screen.

Advantage :
  1. Useful for Modern Complier like GCC.
  2. Useful for the window.
  3. Useful for Turbo C compiler
Disadvantage :
  1. This is only used for window system.

Example :

After clear the output

Explanation :

In the given program we have used the system(“cls”) function to clear the screen. in the first step, it prints “ hello “ and the getch will wait to accept a character and doesn’t echo it on the screen.
Then system(“cls”) will clear the previous output and print the next statement World on the console.


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