What are the default file pointers of  a program in c?

Default File Pointers in C

Introduction

File pointers are essential elements in C programming for performing input and output operations on files. When you open a file in a C program, a file pointer is created automatically to keep track of the current position within the file. There are three default file pointers that every C program has access to:

1. stdin

• Description: stdin stands for standard input. It is a predefined file pointer that is associated with the standard input device, which is usually the keyboard.

• Use: stdin is used to read data from the standard input device.

• Example:

int num;
printf("Enter a number: ");
scanf("%d", &num);

2. stdout

• Description: stdout stands for standard output. It is a predefined file pointer associated with the standard output device, which is usually the console or terminal.

• Use: stdout is used to write data to the standard output device.

• Example:

printf("Hello, World!\n");

3. stderr

• Description: stderr stands for standard error. It is a predefined file pointer associated with the standard error device, which is also typically the console or terminal.

• Use: stderr is used to report error messages and diagnostics.

• Example:

fprintf(stderr, "Error: Division by zero\n");

These file pointers are defined in the header file.

By default, all file operations, such as reading and writing, are performed on these default file pointers. However, it is also possible to open other files and create new file pointers.

Example of how to use the default file pointers:

#include 

int main() {
  char c;

  // Read a character from the standard input stream
  c = fgetc(stdin);

  // Write the character to the standard output stream
  fputc(c, stdout);

  // Return 0 to indicate success
  return 0;
}

When this program is run, it will prompt the user to enter a character. The user's input will be read using the fgetc() function, which uses the stdin file pointer. The input character will then be written to the console using the fputc() function, which uses the stdout file pointer.

It is important to note that the default file pointers should not be closed. Closing a default file pointer can lead to unexpected behavior.

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Conclusion

Understanding and utilizing these default file pointers (stdin, stdout, and stderr) is crucial for effective input and output operations in C programming. By knowing how to use these pointers, you can perform various tasks such as reading user input, displaying output, and reporting errors in your programs.