Last Updated on August 18, 2023 by Mayank Dham
In the realm of C programming, a multitude of functions and commands are at the programmer’s disposal to manage input and output operations. Among these, the fflush function in C stands as a fundamental tool for controlling output buffers. While many developers are well-versed in the mechanics of input and output functions, the nuances of buffer handling can sometimes remain elusive. This article delves into the intricacies of the fflush function in C, uncovering its meaning, purpose, and usage. Whether you’re a novice programmer seeking a comprehensive understanding or an experienced coder looking to fine-tune your I/O operations, this exploration of fflush will shed light on a crucial aspect of C programming. From its syntax to its significance, let’s embark on a journey to demystify the role of fflush in the C programming language.
What is fflush() in C?
fflush in C is a library function used to flush the output buffer of a stream. It is used to write all pending data from the output buffer to the file associated with the stream. fflush() ensures that the data is written to the file before the program moves on to other operations.
The fflush function in C is used to flush the buffer of any stream present in RAM, which means it prints the data of the buffer to the corresponding file in the main memory. The function fflush in C is defined in the header file < stdio.h>.
Syntax of fflush() in C
The syntax of the fflush function in C is as follows:
int fflush(FILE *stream);The fflush in c function is used to flush (or empty) the output buffer of a stream. It takes a pointer to a FILE structure that represents the stream to be flushed. If the stream is NULL, fflush flushes all output streams.
Return Value of fflush() in C
The fflush() function returns the value 0 if it successfully deletes the buffer. It returns EOF if an error occurs.
Parameters fflush() in C
In C, the fflush() function accepts only one parameter: a pointer to the File Object in which we want to flush or write our data. The best examples of File Objects are stdout, stderr, and so on.
Example of fflush() in C
Here is an example of fflush in C with output and explanation:
#include <stdio.h>
int main() {
FILE *fp;
fp = fopen("test.txt", "w");
fputs("Hello World!", fp);
fflush(fp);
fclose(fp);
printf("Data written to the file successfully.\n");
return 0;
}
Output
Data written to the file successfully.Explanation:
In this example, we first include the necessary header file, which is < stdio.h>. We then declare a file pointer called fp.Next, we use the fopen() function to create a new file called test.txt in write mode. We then use the fputs() function to write the string "Hello World!" to the file. After that, we call fflush() to ensure that the data is written to the file immediately. Finally, we close the file using fclose() and print a message to indicate that the data was written to the file successfully.Here,fflush() is necessary because, without it, the program might continue to execute before the data is written to the file. This could result in the data being lost or corrupted.
By calling fflush(), we ensure that the data is written to the file before the program moves on to other operations.
Use of fflush() in C
Here we have use of fflush() in C
- fflush() is used to flush the output buffer of a stream.Output to a stream is usually buffered, meaning that it is stored in memory and not immediately written to the file or other output destination. This buffering improves performance.
- fflush() is often used in conjunction with file I/O operations, to ensure that data is written to disc immediately, rather than being held in memory.
- fflush() can also be used with other types of output streams, such as network sockets or pipes.
Conclusion
fflush() is an essential function when working with files in C. It ensures that data is written correctly to the file by flushing the output buffer associated with the stream. While fflush() can slow down the performance of a program, it’s necessary to ensure that data is written to the file before the program moves on to other operations. Buffer is a "temporary memory" that stores the output before printing it to the main destination. When the buffer is full, the end line character (n) is encountered, or the output is provided by the unbuffered function, the buffer is empty. In C, the fflush() function is used to flush the buffer of any stream and print the data from the buffer to the appropriate file. The function fflush() in C is defined in the. fflush in C function takes only one parameter, a pointer to the File Object in which we want to flush or write our data.
Frequently Asked Questions
Here are the FAQ on fflush in C
Q1. When should fflush in c be used?
Ans. fflush() should be used when it is important that data written to a file or other output stream is immediately physically written to the device.
Q2. Can fflush in c be used with binary files?
Ans. Yes, fflush in c can be used with binary files.
Q3. What happens if fflush() fails?
Ans. If fflush() fails, it returns a non-zero value, indicating that an error occurred. In this case, you may want to use the ferror() function to get more information about the error.
Q4. Is fflush() portable across different operating systems?
Ans. Yes, fflush() is part of the C standard library, and is therefore portable across different operating systems and platforms.
Q5. Can fflush() be used with standard input or error streams?
Ans. No, fflush() can only be used with output streams. Standard input and error streams are input streams, and cannot be flushed using fflush().
Q6. What happens if fflush() is not used?
Ans. If fflush() is not used, any data that has been written to a file or other output stream may be held in memory waiting to be written later.
Q7. Can fflush() be used with input streams?
Ans. No, fflush() can only be used with output streams.
Q8. Are there any potential performance issues associated with fflush()?
Ans. Yes, calling fflush in c can be a relatively slow operation, especially if the output stream is associated with a slow device such as a disk drive.