When do you need to use fflush stdin in C programming?

The fflush function can be used to refresh a stream, which can be used to prevent the memory address from being full, when the stream is pointed to the user's standard input (stdin), it can clear the content in the current buffer, and the input return will also be clear, for example, using fflush(stdin) after scanf() is to automatically clear all the data in the input stream buffer when the input buffer (memory) is full, in fact, the memory is so large now, the data entered each time is only a few bytes, It is almost not used, and the most used place is in embedded development, because there is generally only a few tens of K space on each solidified chip, so the space is very important, and it will be used at this time.

1. flush(stdin) refreshes the standard input buffer and discards the contents of the input buffer.

fflush(stdout) flushes the stdout buffer and prints the contents of the output buffer to the stdout device.

2. When the scanf() function receives the input data, it ends the input of a data in the following situations: (instead of ending the scanf function, the scanf function only has data in each data field and ends after pressing enter).

When encountering a space, "Enter", "Skip Grid" key.

End of the width.

In case of illegal import.

The keyboard buffer may have residual information.

The scanf() function should just scan the stdin stream, and this remnant is in stdin.

To solve this, add fflush(stdin) to the end of the scanf() function.

After you accept the keyboard data, if you do not use the clear stream function to release the memory, then it may cause you to start the input data can not be received, but accept the last data, so generally when receiving the keyboard input will use fflush(stdin), although some data you can be sure to receive, but in order to normalize and avoid errors, we will write fflush(stdin).

This is usually after the input, e.g. after scanf(). Because the carriage return symbol will remain in the buffer, fflush(stdin) is needed to clear the carriage return and other useless symbols, and clear the buffer so that the remaining useless symbols from the previous one are entered into the variable the second time scanf().

stdin is the default input device. It's the keyboard. You can only read data from the input buffer, not write data to it.

scanf() is fscanf(stdin,..If you want other programs to accept, you can write disk files. Your program writes, and other programs read.

The default output device is stdout.

To be able to accept it in other programs, it needs to be through inter-process communication!

For example, sockets, shared memory, pipes, queues, etc.

Don't cry! MSDN is a beacon of VC learning! Of course, there is also information available on the Internet. It should be said that you are very happy now!

Clear the cache of a standard input device (typically a keyboard). It is often suitable for intercepting and entering special values, such as reading one input character at a time, but if you hit enter after entering a character, enter is a special key, which will produce 2 characters, so the program will think that you have entered 3 characters, at this time, you can use this function to clear the keyboard cache after reading a character, so as to clear the impact of carriage enter.

This is used to clear the cache data after input, for example, if you write a program that only allows you to enter numbers, and then you can loop, if you enter a character at this time, then a character is illegal, and it has been kept in the cache space, and if you don't dispose of it, it may be an endless loop....At this point, you can use this **Clear Cache....

Functions are contained in header files and are used to force the contents of the buffer to be written to the file.

2.Function prototype: int

fflush(file

stream)

3.Function function: Clear a stream, that is, clear the file buffer, and write the contents of the buffer to the file when the file is opened in write mode. That is, for ANSI

c specifies the buffer file system, and the function fflush is used to output the contents of the buffer to the file.

4.Function return value: If the refresh is successful, fflush returns 0. The specified stream returns a value of 0 when it has no buffer or is read-only. Returning EOF points out an error.

5.Here's a concrete example to illustrate the method used by this function:

#include

#include

intmain(void)

charch=

c';inti;

for(i=0;

i<5;

i++)fclose(fp);

return0;}

Note: If you call the function fclose to close the file after writing it, you can also write the contents of the buffer to the file, but it will be more expensive.

fflush(stdin) flushes the standard input buffer and discards the contents of the input buffer.

fflush(stdout) flushes the annotation output buffer and prints the contents of the output buffer to the standard output device.

Clear the file buffer, write the contents of the buffer to the file when the file is opened in write mode, without the one you said later.

Example: include

#include

#include

#include

void flush(file *stream);

int main(void)

void flush(file *stream)

When using the scanf() function in C to accept character data on the keyboard, you must use fflush(stdin) to know the last stored data, otherwise the character data will not be stored correctly.

To ensure that the next input is ground and there is no carriage return error before reading, you can choose to use the fflush(stdin) function to flush the buffer.