Notes on Text Files in C

Learning Outcomes

• Understand how to stream data using standard library functions to access persistent text.

Introduction

• Secondary Storage: Retains information when a computer is turned off and allows access by different programs. Information is stored in the form of files.
• Chapter Goals: Describe how to connect a program to a file, store and retrieve information.

Files

• Definition: A named area of secondary storage.
  • Can be fragmented across non-contiguous locations.
  • Distinguished by an end-of-file mark (EOF, typically -1).

Text Format

• Formats: Text and binary.
  • Text Format: Readable and editable data suitable for text editors. Portable across platforms with the same character set.
  • Character Set Standard: IEC/ISO 646-1083.
    • Includes letters, digits, space, control characters, and graphic characters (excludes $ and `).`

Sequential Access

• Access data sequentially, byte by byte, until EOF is reached.

File Connections in C

• Connecting to a File: Use a FILE type object to hold file information and track access position.
  • Declaration: #include <stdio.h> FILE *fp = NULL;
  • Pointer: Initialize to NULL to avoid premature dereferencing.*

Opening a File

• Function: fopen() opens a file and returns a FILE object address.
  • Parameters: file_name[], mode[] (e.g., "r", "w", "a").
  • Example: Open "alpha.txt" for writing with fopen("alpha.txt", "w");
• Failure: Returns NULL if it fails due to permissions or other issues.

Closing a File

• Function: fclose() disconnects the file from the program.
  • Successful Return: 0; Unsuccessful: EOF.
  • Example: Close "alpha.txt" with fclose(fp);

File Communication in C

• Functions:
  • fprintf(): Formatted write.
  • fputc(): Write single character.
  • fscanf(): Formatted read.
  • fgetc(): Read single character.

Writing

• Formatted Writing: fprintf() controls format.
  • Prototype: int fprintf(FILE *, const char [], ...);
• Unformatted Writing: fputc() writes a single character.
  • Prototype: int fputc(int ch, FILE *fp);

Reading

• Formatted Reading: fscanf() reads bytes under format control.
  • Prototype: int fscanf(FILE *, const char [], ...);
• Unformatted Reading: fgetc() reads a single character.*

Managing File State

• Functions:
  • rewind(): Resets pointer to beginning of file.
  • feof(): Checks if end-of-file has been read.

Rewind

• Purpose: Resets the file pointer without disconnecting the file.

End of File

• Functionality: feof() returns true if end-of-file mark was read.

Comparison of File I/O and Standard I/O Functions

• Similarities in function prototypes and return types between file I/O and standard I/O functions.
• Important to check return values, especially for EOF indications.